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Document Name: RIMAP Application Workbook for Power Plants Document Date: Document Author/s: Reference Number: Version
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Document Name:
RIMAP Application Workbook for Power Plants
Document Date: Document Author/s: Reference Number: Version: Contract Number:
26.03.2003 RIMAP Consortium 4-41-W-2002-01-0 Final G1RD-CT-2001-03008
RIMAP Consortium Det Norske Veritas AS (DNV)
ExxonMobil Chemical Ltd. (Exxon)
Bureau Veritas (BV)
Energie Baden-Württemberg AG (EnBW)
Staatliche Materialprüfungsanstalt (MPA)
TÜV Industrie Service, TÜV SÜD Group
Siemens AG (Siemens) Joint Research Centre of the European Commission (JRC) Electricity Supply Board (ESB)
TNO Industrial Technology (TNO)
Corus Ltd.
Hydro Agri Sluiskil B.V. (Norsk Hydro)
The Dow Chemical Company N.V. (DOW)
Mitsui Babcock Energy Ltd. (MBEL)
Solvay S.A.
VTT Industrial Systems (VTT)
No distribution outside RIMAP Consortium No distribution outside RIMAP Thematic Network No distribution without prior approval by RIMAP Consortium Unrestricted distribution
© COPYRIGHT 2004 THE RIMAP Consortium This document may not be copied, reproduced, or modified in whole or in part for any purpose without written permission from the RIMAP Consortium. In addition, to such written permission to copy, acknowledgement of the authors of the document and all applicable portions of the copyright notice must be clearly referenced. All rights reserved
Risk Based Inspection and Maintenance procedures for European industry Risk based Inspection and MAintenance Procedures for European industry (RIMAP) is an EU funded initiative1. RIMAP consists of 3 projects: a research and technological development project (RTD), a demonstration project (DEMO) and a Thematic Network (TN). The background for the RIMAP project is that current practice to inspection and maintenance planning for most industries is based on tradition and prescriptive rules, rather than being an optimized process where risk measures for safety and economy are integrated. New technology for taking risk based decisions is emerging in a broad range of sectors, and they have proven to be a very efficient tool. There is a great need to define the technical content, links to local legislation and to integrate this approach with the day-to-day operation of the plants. The RIMAP project shall: • Develop a unified approach to risk based inspection and maintenance planning. • Set requirements to the contents of an analysis, personnel qualifications, and tools. • Provide the basis for future standardisation within risk based inspection and maintenance. The work in the RIMAP RTD project has been organised as follows: • WP1: Current practice within the involved industries. • WP2: Development of a generic RBIM method, based on a multi-criteria decision process. • WP3: Development of detailed risk assessment methods, damage models for different industry sectors, the use of inspection data. • WP4: Development of RIMAP application workbooks: guidelines for development of Risk Based Inspection and Maintenance plans. • WP5: Validation of the RIMAP methodology. RIMAP RTD reporting structure is given in below: RIMAP Documentation Level - I
D2.2
Exec. Summary & Introduction to RIMAP RIMAP Procedure
D2.1
RIMAP Framework
Requirements
RIMAP Validation / Benchmarking
Overview Document (D3.1) RIMAP Documentation Level - II Damage Mechanisms
RIMAP Tools
NDT Efficiency
Human factors
PoF
CoF
D3.1 and I3.x as Appendices to D3.1 RIMAP Documentation Level - III RIMAP Application Workbooks
Power
Petrochemical
Steel
Chemical
D4.x
WP 5 RIMAP Validation/Benchmarking
The RIMAP DEMO project consists of four demonstration cases, one for each of the involved industry sectors: petrochemical, power, steel, and chemical industry. The techniques can easily be extended to other industry sectors. The RIMAP TN accompanies the RTD and DEMO projects by disseminating the information, and results of the RTD and DEMO part to a wider community of companies that review results and generate an overall industry acceptance.
1
The RIMAP project would like to acknowledge the financial support by the European Commission for the "GROWTH Programme, Research Project RIMAP Risk Based Inspection and Maintenance Procedures for European Industry "; Contract Number G1RD-CT-2001-03008. Without this support it would not have been possible to complete this work.
GROWTH Project G1RD-CT-2001-03008 “RIMAP” Document title: RIMAP Application Workbook for Power Industry Document number: 4-41-W-2002-01-0
Table of contents 1.
CONCLUSIVE SUMMARY ...........................................................................................12
2.
INTRODUCTION...........................................................................................................12 2.1 2.2 2.3
3.
GENERAL .................................................................................................................12 REQUIREMENTS AND SCOPE .....................................................................................13 HOW TO USE THIS DOCUMENT ...................................................................................15 RIMAP PROCEDURE FOR POWER PLANT COMPONENTS....................................16
3.1 GENERAL .................................................................................................................16 3.2 STANDARD FORMAT FOR EACH STEP .........................................................................17 3.3 PREPARATORY ANALYSIS .........................................................................................18 3.3.1 General ..........................................................................................................18 3.3.1.1 3.3.1.2 3.3.1.3 3.3.1.4 3.3.1.5
3.3.2
Description ........................................................................................................................... 18 Requirements....................................................................................................................... 18 Input ..................................................................................................................................... 19 Procedure/flowcharts............................................................................................................ 19 Output .................................................................................................................................. 19
Definition of boundaries ..............................................................................19
3.3.2.1 3.3.2.2 3.3.2.3 3.3.2.4
3.3.3
Description ........................................................................................................................... 19 Output .................................................................................................................................. 20 Definition of objectives and scope........................................................................................ 20 Description ........................................................................................................................... 20
Regulatory requirements .............................................................................20
3.3.3.1
3.3.4
Description ........................................................................................................................... 20
Engineering criteria ......................................................................................20
3.3.4.1 3.3.4.2 3.3.4.3 3.3.4.4 3.3.4.5
3.3.5
Description ........................................................................................................................... 20 Requirements....................................................................................................................... 20 Input ..................................................................................................................................... 20 Warnings, applicability limits ................................................................................................ 20 Examples ............................................................................................................................. 20
Risk acceptance criteria...............................................................................21
3.3.5.1 3.3.5.2 3.3.5.3
3.3.6
Description ........................................................................................................................... 21 Requirements....................................................................................................................... 22 Examples ............................................................................................................................. 23
Preliminary Identification of hazards..........................................................25
3.3.6.1 Description ........................................................................................................................... 25 3.3.6.2 Requirements....................................................................................................................... 27 3.3.6.3 Input ..................................................................................................................................... 27 3.3.6.4 Procedure/flowcharts............................................................................................................ 28 3.3.6.5 Output .................................................................................................................................. 29 DATA COLLECTION AND VALIDATION .........................................................................29
3.4 3.4.1
General ..........................................................................................................29
3.4.1.1 3.4.1.2
3.4.2
Description ........................................................................................................................... 29 Requirements....................................................................................................................... 29
Design, manufacturing, construction data.................................................30
3.4.2.1
3.4.3
Description ........................................................................................................................... 30
Operating and equipment history ...............................................................30
3.4.3.1
3.4.4
Description ........................................................................................................................... 30
Generic/equivalent data ...............................................................................31
3.4.4.1
Description ........................................................................................................................... 31
3.5 MULTILEVEL RISK ANALYSIS AND DECISION MAKING ..................................................31 3.5.1 General ..........................................................................................................32 3.5.1.1
3.5.2
Description ........................................................................................................................... 32
Risk screening ..............................................................................................33
3.5.2.1
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Description ........................................................................................................................... 33
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GROWTH Project G1RD-CT-2001-03008 “RIMAP” Document title: RIMAP Application Workbook for Power Industry Document number: 4-41-W-2002-01-0 3.5.2.2 3.5.2.3 3.5.2.4 3.5.2.5 3.5.2.6 3.5.2.7 3.5.2.8
3.5.3
Requirements....................................................................................................................... 34 Input ..................................................................................................................................... 34 Procedure/flowcharts............................................................................................................ 35 Minimal (adequate) measures.............................................................................................. 37 Output .................................................................................................................................. 37 Warnings, applicability limits ................................................................................................ 37 Tools .................................................................................................................................... 37
Detailed analysis...........................................................................................37
3.5.3.1 3.5.3.2 3.5.3.3 3.5.3.4 3.5.3.5 3.5.3.6 3.5.3.7 3.5.3.8 3.5.3.9 3.5.3.10 3.5.3.11 3.5.3.12 3.5.3.13 3.5.3.14 3.5.3.15 3.5.3.16 3.5.3.17
3.5.4
Description ........................................................................................................................... 37 Requirements....................................................................................................................... 37 Input ..................................................................................................................................... 38 Identify relevant damage mechanisms and failure modes.................................................... 38 Determine likelihood / probability of failure........................................................................... 38 Determine consequence of failure........................................................................................ 39 Procedure/flowcharts............................................................................................................ 40 Construct equipment hierarchy ............................................................................................ 40 Identify relevant damage mechanisms and failure modes.................................................... 41 Determine probability of failure............................................................................................. 41 Determine consequence of failure........................................................................................ 41 Consider conservative inspection/maintenance ................................................................... 42 Risk assessment .................................................................................................................. 42 Decision logic ....................................................................................................................... 42 Output .................................................................................................................................. 44 Warnings, applicability limits ................................................................................................ 44 Tools .................................................................................................................................... 44
Multilevel analysis ........................................................................................44
3.5.4.1 Examples ............................................................................................................................. 44 IMPLEMENTATION OF PLANS .....................................................................................45
3.6 3.6.1 3.6.2
General ..........................................................................................................45 Development of the I&M plan ......................................................................45
3.6.2.1 3.6.2.2 3.6.2.3 3.6.2.4 3.6.2.5 3.6.2.6
3.6.3 3.6.4
Description ........................................................................................................................... 45 Requirements....................................................................................................................... 46 Input ..................................................................................................................................... 46 Procedure/flowcharts............................................................................................................ 47 Output .................................................................................................................................. 47 Warnings, applicability limits ................................................................................................ 48
Examples .......................................................................................................48 Execution of the I&M plan............................................................................48
3.6.4.1 Description ........................................................................................................................... 48 3.6.4.2 Requirements....................................................................................................................... 49 3.6.4.3 Input ..................................................................................................................................... 49 3.6.4.4 Procedure/flowcharts............................................................................................................ 49 3.6.4.5 Output .................................................................................................................................. 49 EVALUATION OF THE PROCESS .................................................................................50
3.7 3.7.1 3.7.2 3.7.3
Description ....................................................................................................50 Requirements................................................................................................50 Input ...............................................................................................................50
3.7.3.1 3.7.3.2
3.7.4
Assessment of effectiveness................................................................................................ 50 Reassessment of risk ........................................................................................................... 51
Procedure/flowchart .....................................................................................51
3.7.4.1 3.7.4.2
3.7.5
Assessment of effectiveness................................................................................................ 51 Reassessment of risk ........................................................................................................... 51
Output ............................................................................................................52
3.7.5.1 3.7.5.2
3.7.6
Assessment of effectiveness................................................................................................ 52 Reassessment of risk ........................................................................................................... 52
Warnings, applicability limits ......................................................................52
4. PROBLEM AND HAZARD IDENTIFICATION – DAMAGE MECHANISMS, PLANT HIERARCHY ..........................................................................................................................52 4.1 DAMAGE SYSTEMATICS ............................................................................................53 4.1.1 WHERE to look for (inspect / monitor) for which type of damage ...........55 Revision number: 0
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HOW to look for (inspect / monitor) for which type of damage................59 4.1.2 4.1.3 How to analyse and predict development of given types of damage ......64 4.2 PLANT BREAKDOWN - STANDARD POWER PLANT HIERARCHY FOR RBI / RBLM: WHAT KIND OF PROBLEMS ARE MOST LIKELY TO APPEAR AND WHERE .............................................67 4.2.1 RIMAP Power Plant Standard Hierarchy ....................................................67 4.2.2 Example of plant hierarchy from process industry ...................................71 4.2.3 Hierarchy vs. Problems covered by the RIMAP Power Workbook...........73 5.
MULTILEVEL RISK ANALYSIS...................................................................................79 5.1 5.2 5.3 5.4
INTRODUCTION .........................................................................................................79 PROBABILITY OF FAILURE DETERMINATION ...............................................................79 CONSEQUENCE OF FAILURE DETERMINATION ...........................................................82 RISK – GETTING A “BOW TIE” ..................................................................................82
6. STANDARD DATA FORMAT FOR THE RBI/RBLM IN RIMAP WORKBOOK FOR POWER PLANTS ..................................................................................................................82 6.1 FORMAT FOR SYSTEM / COMPONENT RECORDS.........................................................82 6.2 FORMAT FOR PROBLEM RELATED RECORDS .............................................................84 6.3 EXAMPLE “FORMATTING” OF INFORMATION FOR THE PURPOSE OF RBLM ANALYSIS: ECONOMIZER (HAC) ........................................................................................................85 6.4 BOILER GENERAL ....................................................................................................86 6.5 BOILER TUBES .........................................................................................................91 6.6 ECONOMIZER TUBING ...............................................................................................95 6.7 PROBLEM #1: ECONOMISER TUBE FAILURES DUE TO WALL THINNING.......................103 6.8 PROBLEM #2: ECONOMISER CRACKING ..................................................................106 7.
WORKED EXAMPLES ...............................................................................................109 7.1 MULTILEVEL RISK ANALYSIS – POWER PLANT ..........................................................109 7.1.1 Technical background................................................................................109 7.1.2 Sample case ................................................................................................113 7.1.3 Screening level ...........................................................................................114 7.1.4 Intermediate level .......................................................................................120 7.1.5 Detailed level...............................................................................................121 7.2 EXAMPLES FROM PROCESS INDUSTRY.....................................................................124 7.2.1 Example of PoF calculation for distillation tower overhead system .....124 7.2.1.1 7.2.1.2 7.2.1.3 7.2.1.4
7.2.2
Design information ..............................................................................................................124 Process information ............................................................................................................124 Corrosion information ..........................................................................................................125 Pof Calculation ....................................................................................................................126
Example of PoF calculation for HF stripper top.......................................130
7.2.2.1 7.2.2.2 7.2.2.3 7.2.2.4 7.2.2.5 7.2.2.6
Calculation process .............................................................................................................130 Design information ..............................................................................................................130 Process information ............................................................................................................130 Corrosion information ..........................................................................................................131 Inspection history ................................................................................................................131 PoF calculation....................................................................................................................131
8.
RISK CONSIDERATION ............................................................................................132
9.
CONCLUSIONS..........................................................................................................132
10.
REFERENCES ...........................................................................................................133
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List of tables TABLE 2-1 SCOPE OF THE WORKBOOK CONCERNING MAIN SYSTEMS .........................................14 TABLE 2-2 “ROAD MAP” OF THE DOCUMENT .............................................................................15 TABLE 3-1 EXAMPLES OF ENGINEERING CRITERIA FOR DETERMINING A FAILURE........................21 TABLE 3-2 RISK CRITERIA........................................................................................................21 TABLE 3-3 INDIVIDUAL RISK FOR PUBLIC. .................................................................................23 TABLE 3-4 INDIVIDUAL RISK FOR WORKERS. ............................................................................24 TABLE 3-5 SOCIETAL RISK FOR PUBLIC. ..................................................................................24 TABLE 3-6 SOCIETAL RISK FOR WORKERS...............................................................................24 TABLE 3-7 INFORMATION REQUIREMENTS.................................................................................30 TABLE 3-8 COMPONENT FAILURE DATABASE CONSIDERATIONS.................................................31 TABLE 3-9 EXAMPLES OF DECISION LOGIC APPLICATION...........................................................43 TABLE 4-1 TYPES OF IN-SERVICE DAMAGE AND THEIR SPECIFICS: CLASSIFICATION ADOPTED IN THIS WORK.......................................................................................................................54 TABLE 4-2 CLASSIFICATION OF TYPE OF DAMAGE VS. SYSTEMS/COMPONENTS IN DIFFERENT TYPES OF PLANTS (FPP – FOSSIL POWER PLANTS, NPP – NUCLEAR POWER PLANTS, PRP – PROCESS PLANTS; WELD CRITICAL IN ALL COMPONENTS) ..................................................56 TABLE 4-3 CLASSIFICATION OF TYPE OF DAMAGE VS. PRIORITIZED METHODS OF INSPECTION.....60 TABLE 4-4 SUGGESTED MEASURES FOR PRE-SYMPTOM APPEARANCE MEASURES LEADING TO EARLY DISCOVERY OF DAMAGE IN PLANTS ........................................................................63 TABLE 4-5 SUGGESTED METHODS FOR THE ANALYSIS DEPENDING ON DAMAGE TYPES...............65 TABLE 4-6 RIMAP POWER PLANT HIERARCHY .........................................................................68 TABLE 4-7 EXAMPLE OF TYPICAL PROCESS PLANT BREAKDOWN (PLANT / UNIT / SUB-UNIT) ......71 TABLE 4-8 EXAMPLE OF LIST OF PROCESS EQUIPMENT WITH MAIN TECHNOLOGIES ....................72 TABLE 4-9 LIST OF PROCESS SUB EQUIPMENT - EXAMPLE .........................................................73 TABLE 4-10 AN EXAMPLE OF LINKING COMPONENTS, DAMAGE MECHANISMS AND INSPECTIONS TECHNIQUES (EPRI).........................................................................................................74 TABLE 4-11 AN EXAMPLE OF LINKING COMPONENTS, DAMAGE MECHANISMS AND INSPECTIONS TECHNIQUES (INNOGY)...................................................................................................75 TABLE 4-12 HRSG COMPONENTS AND THEIR VULNERABILITY TO DAMAGING MECHANISMS (PASHA, ALLEN, 2003) ....................................................................................................76 TABLE 4-13 COMPONENT HIERARCHY VS. PROBLEMS ...............................................................78 TABLE 6-1 TYPICAL DESIGN CONDITIONS FOR 400MW PULVERIZED COAL FIRED BOILERS..........87 TABLE 6-2 FORCED AND SCHEDULED OUTAGES AND DERATINGS OF BOILERS (NERC GADS DATA 1992-1996)............................................................................................................89 TABLE 6-3 BOILER TUBE FAILURE MECHANISMS. ......................................................................92 TABLE 6-4 LOSS OF AVAILABILITY DUE TO BOILER TUBE FAILURES (A.F. ARMOR, R.H.WOLK, PRODUCTIVITY IMPROVEMENT HANDBOOK FOR FOSSIL STEAM POWER PLANTS, EPRI, SEPTEMBER,1998.)..........................................................................................................94 TABLE 7-1 COMPONENT DESIGN DATA....................................................................................114 TABLE 7-2 CALCULATED COMPONENT EXHAUSTION VALUES ...................................................115 TABLE 7-3 DISTILLATION TOWER TOP PART - PROCESS ..........................................................124 TABLE 7-4 PROBABILITY OF FAILURE AFTER 5 YEARS .............................................................126 TABLE 7-5 ASSUMED VALUE OF POF BEFORE ANY INSPECTION ...............................................126 TABLE 7-6 VALUE OF PROBABILITY AFTER THE 1ST INSPECTION ...............................................127 TABLE 7-7 POF RESULTS AFTER COMPLETION OF A HIGHLY EFFECTIVE INSPECTION ................127 TABLE 7-8 POF RESULTS AFTER COMPLETION OF A USUALLY EFFECTIVE INSPECTION .............127 TABLE 7-9 POF RESULTS AFTER COMPLETION OF A FAIRLY EFFECTIVE INSPECTION .................127 TABLE 7-10 PROBABILITY OF FAILURE AFTER 5 YEARS ...........................................................128 TABLE 7-11 ASSUMED VALUE OF POF BEFORE ANY INSPECTION .............................................128 TABLE 7-12 VALUE OF PROBABILITY AFTER THE 1ST INSPECTION .............................................129 TABLE 7-13 POF RESULTS AFTER COMPLETION OF A HIGHLY EFFECTIVE INSPECTION ..............129 TABLE 7-14 POF RESULTS AFTER COMPLETION OF A USUALLY EFFECTIVE INSPECTION ...........129 Revision number: 0
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TABLE 7-15 POF RESULTS AFTER COMPLETION OF A FAIRLY EFFECTIVE INSPECTION ...............129 TABLE 7-16 DISTILLATION TOWER TOP PART - PROCESS ........................................................131 TABLE 7-17 HYDROGEN EMBRITTLEMENT CORROSION DATA ...................................................131
List of figures FIGURE 1-1 POWER INDUSTRY APPLICATION WORKBOOK IN RIMAP FRAMEWORK ...................12 FIGURE 2-1 RIMAP APPLICATION WORKBOOK FOR POWER INDUSTRY STRUCTURE ..................13 FIGURE 3-1 BASIC REPRESENTATION OF RIMAP PROCEDURE...................................................17 FIGURE 3-2 EXAMPLE OF RISK MATRIX.....................................................................................22 FIGURE 3-3 PROCEDURE FOR THE IDENTIFICATION OF HAZARDS................................................28 FIGURE 3-4 RISK SCREENING. ..................................................................................................33 FIGURE 3-5 SCREENING RISK MATRIX ......................................................................................36 FIGURE 3-6 DETAILED ASSESSMENT .........................................................................................40 FIGURE 3-7 DECISION LOGIC....................................................................................................43 FIGURE 3-8 EXAMPLE OF POF (LOF) CALCULATION..................................................................44 FIGURE 3-9 EXAMPLE OF POF (LOF) ISSUES IN PRACTICE (POWER PLANT)................................45 FIGURE 3-10 EVALUATION OF THE RISK-BASED DECISION MAKING PROCESS.............................52 FIGURE 4-1 DAMAGE CONSIDERATIONS IN THIS WORKBOOK ......................................................53 FIGURE 4-2 EXAMPLE OF TYPICAL HIERARCHY (BREAKDOWN) STRUCTURE; USUALLY THE LEVELS ARE OPTIONAL AND THE PROBLEM/ISSUE SUB HIERARCHY CAN BE ATTACHED AT VIRTUALLY ANY LEVEL .......................................................................................................................68 FIGURE 5-1 SIMPLIFIED BOW TIE MODEL WITH POF ON ONE SIDE AND COF ON THE OTHER ........79 FIGURE 5-2 ELEMENTS OF POF DETERMINATION IN RIMAP ......................................................80 FIGURE 5-3 MULTILEVEL POF ANALYSIS...................................................................................81 FIGURE 6-1 FULL SET OF ELEMENTS FOR THE RBLM ANALYSIS OF THE ECONOMIZER ................85 FIGURE 6-2 THE SUBSET OF ELEMENTS CHOSEN FOR THE RBLM ANALYSIS TAKEN FOR THIS EXAMPLE .........................................................................................................................86 FIGURE 6-3 BOILER HEAT FLOWS (EPRI). ................................................................................87 FIGURE 6-4 TYPICAL BOILER LAYOUT. ......................................................................................88 FIGURE 6-5 MAJOR PROBLEMS IN CYCLING FOSSIL BOILERS (A.F. ARMOR, R.H.WOLK, PRODUCTIVITY IMPROVEMENT HANDBOOK FOR FOSSIL STEAM POWER PLANTS, EPRI, SEPTEMBER,1998.)..........................................................................................................89 FIGURE 6-6 EQUIVALENT UNAVAILABILITY FACTOR (EUF) DUE TO BOILER TUBE FAILURES IN COAL PLANTS LARGER THAN 200 MW (A.F. ARMOR, R.H.WOLK, PRODUCTIVITY IMPROVEMENT HANDBOOK FOR FOSSIL STEAM POWER PLANTS, EPRI, SEPTEMBER,1998.) .......................................................................................................................................91 FIGURE 6-7 CORROSION IN ECONOMISER TUBES .......................................................................96 FIGURE 6-8 DAMAGE AT BUNDLE BRACES OF AN ECONOMISER TUBE .........................................96 FIGURE 6-9 TYPICAL LOCATIONS FOR EROSION, CORROSION, DAMAGE AT BUNDLE BRACES (SPRINT PROJECT SP249, DOCUMENT GG010) ..............................................................97 FIGURE 6-10 DEPENDENCY BETWEEN DIFFERENT FAILURE MODES. .........................................102 FIGURE 7-1 CREEP EXHAUSTION CALCULATION BASED ON TRD (NOW EN 12952)...................110 FIGURE 7-2 TRD FATIGUE CURVE (WITH DERIVED MEAN VALUE CURVE) AT 400°C...................110 FIGURE 7-3 COMPONENT GEOMETRY DATA .............................................................................111 FIGURE 7-4 DESIGN AND OPERATING TEMPERATURE AND PRESSURE ......................................111 FIGURE 7-5 SERVICE TIME OF THE COMPONENT ......................................................................112 FIGURE 7-6 EXAMPLE OF DISTRIBUTION FOR CREEP RUPTURE STRENGTH AT 520°C ................113 FIGURE 7-7 EXAMPLE OF DISTRIBUTION FOR FATIGUE STRENGTH AT 400°C ............................113 FIGURE 7-8 SCREENING LEVEL POF ANALYSIS IN ALIAS-RISK ...............................................116 FIGURE 7-9 DEFINING POF CLASSES USING ALIAS-RISK ........................................................116 FIGURE 7-10 DEFINING COF CLASSES USING ALIAS-RISK .....................................................117
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FIGURE 7-11 BUILDING FAILURE SCENARIOS USING ALIAS-RISK ............................................118 FIGURE 7-12 “BOW TIE” FOR SUPEHEATER COMPONENT ........................................................118 FIGURE 7-13 IMPORTED CALCULATED POF VALUES ................................................................119 FIGURE 7-14 INPUT OF COF VALUES ......................................................................................119 FIGURE 7-15 RISK MAP AFTER SCREENING LEVEL ...................................................................120 FIGURE 7-16 RISK MAP AFTER INTERMEDIATE ANALYSIS .........................................................121 FIGURE 7-17 CREEP CRACK GROWTH WITH C* (FORM FACTOR 2.5) (JOVANOVIC, MAILE, 2001)) .....................................................................................................................................122 FIGURE 7-18 SUPERHEATER COMPONENT ON A RISK MAP AFTER DETAILED ANALYSIS .............122 FIGURE 7-19 EXAMPLE OF CALCULATING POF FOR THE SAMPLE CASE CONSIDERED ...............123 FIGURE 7-20 CALCULATION PROCESS – NON TRENDABLE DAMAGES .......................................130 FIGURE 7-21 API 581 CALCULATION PROCESS FOR NON TRENDABLE DAMAGES ......................132
List of Acronyms The following table provides meanings/explanations for acronyms used in this documents. Acronym AAR ACRS AHP AI AI&DM AIChE / CCPS ALIAS
AMES ASME
BFS
BRITE BS CAD CCM CEC CEGB
CLA CLM CRO DG, DG III, DG XIII
Revision number: 0
Meaning Advanced Assessment Route (in SP249) Advisory Committee on Reactor Safeguards (in the USA) Analytical Hierarchy Process Artificial Intelligence Artificial Intelligence & Data Mining American Institute of Chemical Engineers / Center for Chemical Process Safety, 345 East 47th Street, New York 10017 Advanced modular intelligent Life Assessment Software System, a product of MPA Stuttgart, Germany (see more on http://www.mpa-lifetech.de/) European Network on Ageing Materials Evaluation and Studies American Society of Mechanical Engineers, ASME International, 3 Park Avenue, New York, New York 100 16. (http://www.asme.org/asme/ ) Betriebsführungssystem, Operation Management System, of Siemens company, Germany (http://w2.siemens.de/kwu/e/foa/n/news/kwu047e.htm ) One of the CEC programs for technological R&D in Europe, initially an acronym, nowadays a name of the program only British Standard (http://www.bsi.org.uk/) Computer-aided Design Condition-Centred Maintenance The Commission of the European Communities (http://europa.eu.int/) Central Electricity Generating Board, former nationally owned power utility for England and Wales (see Pollitt, Newbery, 1996) Component (remaining) Life Assessment / Analysis Component Life Management Consulting and Research Organization Directorate General, DG III "Industry", DG XIII " Telecommunications, Information Market and Exploitation of Research"of Page 8 of 135
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Acronym DIN DNV DSS EIA
EnBW EnBW/EVS EnBW/BW ENIQ EPA EPERC EPRI ERA ESR ET EU FBAHP FPP GOPP HAZ HAZOP IEC IP ISS IVO JRC
KI KMS KonTraG KWL MADM MCDM MPA
MT MTBF Revision number: 0
Meaning the CEC (see http://europa.eu.int/comm/dgs_en.htm) Deutsche Industrienorm German Standards (http://www.din.de) Det Norske Veritas, Hovik, Norway (http://www.dnv.no) Decision Support System(s) Energy Information Administration of National Energy Information Center (http://www.eia.doe.gov/), US Department of Energy Energie Baden-Württemberg AG (http://www.enbw.com/index.html) EnBW Energie Versorgung Schwaben AG (http://www.enbw.com/wir/wir.html) EnBW Badenwerk AG (http://www.enbw.com/wir/wir.html) European Network for Inspection Qualification US Environmental Protection Agency, 401 M Street, S.W., Washington, D.C. 20406 European Pressure Equipment Research Council (http://scisj-02.jrc.nl/eperc/ ) Electric Power Research Institute, Palo Alto, USA (http://www.epri.com) ERA Technology Ltd., Leatherhead, UK (http://www.eureka.era.co.uk) Expert System for Remaining Life Assessment, Expertensystem zur Schadens- und Restlebensdaueranalyse Eddy Current inspection European Union (http://europa.eu.int/) Fuzzy-Bayesian Analytical Hierarchy Process Fossil-fired Power Plant Goal-oriented Project Planning Heat affected zone (in welds) Hazard and Operability (see DIN IEC 56/581/CD) International Electrotechnical Commission Inspection Planning Information Software System (as in IEC 61508) Imatran Voima Oy, company (http://www.ivogroup.com) Joint Research Center(s) of The European Community (http://www.jrc.org/jrc/index.asp); for this work relevant those in Petten, The Netherlands and Ispra, Italy Künstliche Intelligenz (artificial intelligence) Knowledge Management System (KMS) Gesetz zur Kontrolle und Transparenz im Unternehmensbereich (KonTraG) v. 27.4.1998, BGB1. I 1998, 786 Kraftwerk Laufenburg, Germany (http://www.kwl.de/) Multi-attribute decision making Multi-criteria decision making (Staatliche) Materialprüfungsanstalt, State Institute for Testing of Materials, Germany; MPA Stuttgart (http://www.mpa.uni-stuttgart.de) Magnetic (particle) testing Mean time between failures Page 9 of 135
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Acronym MVV NDE NDT NESC NFPA NPP OECD OR OSHA PAIS PISC PLAN PLAN-East PM PRA PrP PSA PT R&D RBI RBISI RCM RCLM RLA RLM ROI RP RRLM RT, RX RTD RWE SCADA SCC SIL SME SPM SPRINT
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Meaning (see "") Mannheimer Versorgungs- und Verkehrsgesellschaft mbH, Mannheim, Germany (http://www.mvv.de/) Non-Destructive Examination Non-Destructive Testing Network for Evaluating Steel Components US National Fire Protection Association, 1 Batterymarch Park, Quincy, Massachusetts 02269 Nuclear Power Plant Organization for Economic Cooperation and Development (http://www.oecd.org/) Operation Research (see RWTH http://www.rwth-aachen.de) US Occupational Safety and Health Administration, U.S. Department of Labor, Washington, D.C. 20402 PLAN Horizontal Theme for Advanced Information Systems – a sub-activity in PLAN project (http://www.mpa-lifetech.de ) Programme for the Inspection of Steel Components Plant Life Assessment Network of JRC Petten, CEC countries (see http://sci-sj-02.jrc.nl/plan/index.html) Plant Life Assessment Network of MPA Stuttgart – Countries of Central and Eastern Europe (http://www.mpa-lifetech.de) plant maintenance Probabilistic Risk (Reliability) Assessment (Analysis) Process Plants Probabilistic Safety Analysis) (liquid) Penetrant Testing (Inspection, visible and fluorescent) Research and Development Risk-Based Inspection Risk-Based In-Service Inspection Reliability-Centered Maintenance Risk-informed Component Life Management, Risk-aware Component Life Management (used as a synonym) Remaining Life Assessment / Analysis, Restlebensdaueranalyse Remaining Life Management / Restlebensdauermanagement return of investment Replica Testing Risk-informed Remaining Life Management Radiography testing, X-ray testing (ASME) Research and Technology Development Center (see also http://www.asme.org/asme/) earlier Rheinsch-Westfälische-Elektrizitätswerke, nowadays only RWE Energie (http://www.rweenergie.de/index_eng.htm) Supervisory Control And Data Acquisition Stress Corrosion Cracking Safety Integrity Levels (defined in IEC 61508) small and medium enterprise (a EU-term) Structured Project Management (see ETP http://www.etpint.com) Strategic Programme for Innovation and Technology Transfer (Projects part-funded by DG-XIII of the EU, see above), rePage 10 of 135
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Acronym SRCM SRRA TPM TQM TRD TTF TÜV
US, UT VGB VT VTT XPS FIRE ZT
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Meaning placed in late 1990s by other initiatives like LIFE Streamlined reliability-centered maintenance Structural Reliability Risk Assessment Total Productive Maintenance Total Quality Management Technische Regeln für Dampfkessel, German boiler code Technical Task Force (of EPERC, see e.g. TTF3 http://sci-sj02.jrc.nl/eperc/projects/ttf3.html ) “Technischer Überwachungsverein“ – German inspection and certification bodies, nowadays independent companies (see e. g. http://www.tuev-rheinland.de/) Ultrasonic testing (inspection) Vereinigung der Großkraftwerkbetreiber e. V., Essen, Germany Visual Testing Technical Research Centre of Finland (http://www.vtt.fi/) eXPert System for FIre insurance Risk Evaluation (see also http://www.munichre.com) Emerging testing (inspection) methods and techniques
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1. Conclusive summary This document represents full “hands on”, RIMAP application guide for performing a risk analysis mainly concentrating on the equipment and problems that can be found in power plants. Furthermore it can be used in other types of industries for similar components. The position of this guideline in overall RIMAP framework is shown in Figure 1-1
WP2 RIMAP Framework
RIMAP Procedure
RIMAP Workprocess
RIMAP Guideline D2.2 (covers RIMAP Framework)
Subchapter 7.6 Chapter 8
Appendix of the Guideline, RIMAP Procedure, at different levels/steps D2.1
WP4 DEMO2
RIMAP Application Workbooks
WP3.1
Application Workbook Power Industry D4
RIMAP Procedure Application Reports from RIMAP Demo Project
Figure 1-1 Power Industry Application Workbook in RIMAP Framework The RIMAP procedure is explained here and supported in the following chapters with raw (live) data needed for the analysis and by examples showing the complete process of a risk analysis, from Preparatory analysis to Implementation. The Workbook by it’s structure follows the RIMAP procedure.
2. Introduction 2.1 General According to the RIMAP project work plan (WP4) this report covers the POWER PLANT RELATED PART of RIMAP WP4 deliverables (WP4: RIMAP Application Workbooks). Hence it combines / couples the deliverables: D4.1 Guidelines on how to set up inspection/maintenance program based on risk, cost and experience feedback. Define the main working process involved, here power plants, D4.2 Guideline on how to benchmark an inspection program based on cost, risk and experience, here power plants, D4.3 Workbook per industry sector, here power plants Deliverable D4.3 is, obviously the whole of the workbook. Deliverables D4.1 and D4.2 are provided within the PART I of the workbook while the PART II and PART III give detailed data on item per item basis and describe in detail all elements on assessing the risk, respectively. The deliverables have been merged due to the need to have one document containing virtually all information needed to start and perform an RBI/RBLM analysis (see ).
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Main objective of WP and the Workbook is to describe and specify the use of the RBI/RBLM methodology practically setting up inspection/testing and maintenance program for power plants. The Thematic Network and strong participation of industry partners in the development of the workbook ensure that the workbook developed in WP4 is to be applied and validated in WP5, and applied in the demonstration project. Process Workbook
Chemical Workbook
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
D4.3a
D4.3b
D4.3c
Power Workbook
Additional details for D4.1
Worked Example for D4.1 D4.2 Benchmarking
Workbook Part I
D4.1 Procedure/Process of RBI/RBLM
Additional details for D4.2
WB Part II
OPTIONAL (Internal RIMAP deliverables to participating partners)
Item per Item data
WB Part II
D4.3 Deliverable
Appendices Glossaries...
Figure 2-1 RIMAP Application Workbook for Power Industry structure 2.2 Requirements and scope The report provides answers to the following requirements/elements of RIMAP project Work Plan (for the power plan sector): 1.
Description of the process of the development of an inspection and maintenance program What: to define the scope of inspection/maintenance for each piece of equipment according to probable damage mechanisms It includes the definition of the coverage: (% of total equipment, representative equipment, identification of the hot spots, etc) and the definition of the test points. How: Selection of inspection/maintenance technique which takes the inspection/maintenance effectiveness as well as the considered damage mechanisms into account. When: to do an action several planning techniques are available and will be de-
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2.
3.
scribed (risk criteria. shutdown optimization. regulation, experience and manufacturer recommendations). Documentation: Documentation. In addition the decision logging and data warehouse like (i.e. “temporal”) storing of the decision-relevant data will be assured (elements like who, why etc.). Reduce the risk associated to inspection/maintenance program Apply the consequence (CoF), probability (PoF) and PoD methods defined in WP 3 to: Evaluate the risk associated with the existing inspection/maintenance program Define alternative program with an objective of risk reduction, choosing between replacing, monitoring or testing, and define the way it will be performed Evaluate and compare alternatives program Optimize inspection/maintenance program through cost with constraint on safety and environment effects. Develop workbook per industry sector. For each of the industries one detailed workbook is to be provided, containing: default and/or recommended data for typical components needed for calculation/modeling of ii. Probabilities of occurrence (PoF-, expert judgments, etc.) iii. Consequences (safety. financial, environmental, technical, etc.) 1 – 3 completely elaborated examples, including full set of data needed and explanation of each step in the calculation and interpretation and use of the results obtained. Description of limitation and applicability of models and data
The scope of this version of the workbook, concerning main systems is shown in Table 2-1. All these systems are of course later on, broken down up to component level. In addition Table 2-1 shows also tackled, selected critical systems/components from process industry (Giribone, Pocachard, 2003)
Table 2-1 Scope of the workbook concerning main systems I. Power Industry Solid fuel systems (e.g. distribution and storage) Liquid fuel systems (e.g. transport and storage) Gaseous fuel systems (e.g. transport and storage) Feedwater/boiler water systems (e.g. boiler water transport) Boilers (e.g. boiler tubing, headers and drums ) Steam piping (e.g. main steam piping) Steam turbines (e.g. HP/IP turbine rotors) Gas turbines (e.g. turbine disks) Generators (e.g. rotor, stator) Control systems (e.g. electronics, relays, insulators) Electric distribution (e.g. switchgear) Motors (e.g. windings) II. Process Industry (selected critical systems/components) Reactor Heat exchangers Columns Furnace Air – coolers
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Drums / Pressure vessels Filters Storage tanks Utility Boiler Sphere Piping Compressors Pumps Valves
2.3 How to use this document As already mentioned, this document incorporates all three foreseen deliverables and due to practical reasons it is divided into three parts. The idea was to make, on one hand, the use of the document as simple as possible and on the other, to have one complete document as a standalone guideline for performing a risk analysis in a power plant. When using this document, one should first go trough Chapter 3 which gives the overall guideline on how to set-up and perform a risk analysis. Further chapters give detailed descriptions on some parts of the RIMAP procedure as well as links to other information contained in the workbook (when and if needed). The following table (see Table 2-2) represents a document “road map” and in a way directs the user based on the actions he/she would like to perform.
Table 2-2 “Road map” of the document Action Set-up and perform risk analysis
Where to look See PART I – Chapter 2 which gives guidelines on a higher level on how to set-up and perform a risk analysis from start to the end. Problem and hazard identification See PART I – Chapter 3 which discusses in detail problem and hazard identification as well as plant hierarchy, and also points to appendices where more information can be found Multi-level risk assessment See PART I – Chapter 4 which discuss in detail one of the most important steps of the procedure – determination of Probability/Consequence of Failure in order to assess risk. Gives also links to appendices where more details can be found Which data is needed to perform See PART I – Chapter 5 which gives and describes the risk assessment? the data which can be found in PART II of the workbook. The data given there thoroughly describes systems from the plant going deeply to component/single problem level
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3. RIMAP procedure for power plant components 3.1 General An overview of RIMAP procedure is shown in Figure 3-1. As may be seen, it has only five major technical steps, namely 1. 2. 3. 4. 5.
preparatory analysis data collection MULTILEVEL RISK ANALYSIS decision making and optimization implementation
Additionally one techno-organizational (incl. economy-related aspects) step, namely 6. Assessment/evaluation of efficiency. Furthermore, RIMAP procedure is organized as a double cycle: one that is mainly technical and another that is techno-organizational (management related). Out of these steps, Multilevel Risk Analysis has one more dimension regarding the depth of the required analysis. Corresponding levels are: a. screening (low level analysis) b. intermediate level (levels of) analysis c. Detailed analysis. The respective logical link to qualitative, semi-quantitative and quantitative levels of API, or to Levels I, II and III of EPRI approach () is intuitive and self-explaining.
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Preparatory Analysis
Data collection and Validation
Detailed Analysis Intermediate Analysis Screening Analysis
Multi-level Risk Analysis - PoF - CoF - Risk
Techno-organizational cycle
Technical cycle
Decision making and optimization - Operation - Monitoring - Inspection - Maintenance
Seamless, multi-level, transition from screening to detailed analysis
Implementation - Operation - Monitoring - Inspection - Maintenance
Assessment / Evaluation of Efficiency
Figure 3-1 Basic representation of RIMAP procedure.
3.2 Standard format for each step Each step of the procedure is described trough series of sub-steps. The following structure describes the format for each step. Each procedure step has following main steps and corresponding sub-steps: •
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General 3.2.1 Description 3.2.2 Requirements 3.2.3 Input 3.2.4 Procedure/flowcharts 3.2.5 Output Definition of boundaries 3.2.6 Description 3.2.7 Output Definition of objectives and scope 3.2.8 Description Regulatory requirements 3.2.9 Description and references Engineering criteria Page 17 of 135
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•
•
3.2.10 Description 3.2.11 Requirements 3.2.12 Input 3.2.13 Warnings, applicability limits 3.2.14 Examples Risk acceptance criteria 3.2.15 Description 3.2.16 Requirements 3.2.17 Examples Identification of hazards 3.2.18 Description 3.2.19 Requirements 3.2.20 Input 3.2.21 Procedure/flowcharts 3.2.22 Output
3.3 Preparatory analysis 3.3.1
General
3.3.1.1
Description
This step, which is the very first of RIMAP procedure, has the obvious goal to bring us to the point where we can really begin with the procedure. This means that after the completion of this step, one should know where to perform RIMAP procedure (i.e. plant, system, components, etc.), what he wants to achieve (objectives and scope of the analysis), and a general idea about how to do it. 3.3.1.2
Requirements
A risk based assessment cannot be conducted in isolation. It is unlikely that a single person has the width and depth of knowledge to carry out an assessment successfully. A team approach should and must be encouraged. Hence, at the very beginning, the team having the needed expertise to accomplish RIMAP procedure should be composed. Risk based inspection and maintenance management requires experienced personnel at all levels as well as appropriate routines for the execution of the work. The current relevant standards do not set formal requirements to qualification of the personnel that perform inspection and maintenance planning, even if the execution of inspection and maintenance activities to some extent is regulated through qualification schemes, e.g., ASNT requirements and European standard EN 473. Risk based inspection and maintenance planning requires a multidisciplinary team with competencies within • Inspection and/or maintenance planning requires disciplines engineers, e.g., mechanical, electrical, instrumentation, and engineers with handson experience from inspecting and/or maintaining the equipment under consideration both in-service and during construction. • Inspection planning requiring materials/corrosion personnel with expertise in materials selection, corrosion monitoring and control, chemical treatments, fitness-for-service assessments. • Safety/consequence engineers, i.e., personnel with experience in formal risk analysis covering personnel safety, economic and environmental disciplines. Revision number: 0
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• •
•
Plant operation, process, and maintenance personnel with detailed knowledge of the installation and process to be analysed. Reliability engineering practise/principles should be available for consultation to ensure that the maintenance activities focus on the high risk items, to ensure that the maintenance and inspection plan is cost optimised, and more generally to optimise plant operation. Inspection expertise depending on the local requirements/legislation.
Note that particular cases may require special competencies. In addition local legislation and the type of industry may set detailed requirements to competencies involved. Due consideration should be given to the wide background collated in the team. One or more of the skills may be possessed by one person, but it is emphasised that risk based inspection and maintenance planning is a team effort. The team should then take all appropriate actions so as to assure the acceptance of the methodology and objectives of RIMAP procedure with owner and authorities (notified bodies). 3.3.1.3
Input
This step receives no direct input from another step. However, it receives a feedback from the data collection and validation step. In this way, the data collection step is integrated with the preparatory analysis and the working team can be assured that it has enough data to proceed with the next steps. 3.3.1.4
Procedure/flowcharts
The preparatory analysis consists of the following sub-steps: • decide to perform and setup the RIMAP procedure; start RIMAP procedure • define / limit the system (boundaries) considered for RIMAP procedure Example: Main steam line piping system from the outlet header to the turbine inlet (stop valve) • define objectives Example: Optimize time and extent of next inspection • define scope of analysis, including operating conditions, loads and exceptional situations to be covered (e.g. upsets, accidents, etc.), as well as the operating period covered • define risk acceptance criteria, including regulatory requirements • identify main possible hazards (adverse events) • identify main damage mechanisms (list) • identify main possible failure scenarios • assure acceptance of the methodology and objectives of RIMAP procedure with owner and authorities (notified bodies) 3.3.1.5
Output
The output of this step (i.e. system boundaries, scope of analysis, regulatory requirements, damage mechanisms, etc.) determines every subsequent step.
3.3.2
Definition of boundaries
3.3.2.1
Description
This is a sub-step of the preparatory analysis and serves the purpose of defining the system of interest. It can be the plant as a whole as well as a certain component or even a part of it.
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It is important to ensure that all aspects are covered, e.g. when considering a pump is it just the pump impeller and bowl or does it include the drive mechanism, the power source to the drive. This must be made clear and recorded. 3.3.2.2
Output
The output of this step is a system/component hierarchy in other words a decomposition of the system of interest in its subsystems (i.e. systems, components, parts, locations). Based on this hierarchy, one has then to identify the relevant hazards, damage mechanisms, failure scenarios, etc. (sub-steps of preparatory analysis) and to collect the relevant data (collection data step). 3.3.2.3
Definition of objectives and scope
3.3.2.4
Description
Time frame for analysis When considering time dependent degradation mechanisms it is important that the scenario has a time dimension. This is like posing the question "what is the probability of corrosion leading to a leak within X years". In choosing the time frame it should be sufficiently large to cover period where mitigation steps would be possible. A general guide to time frame should be between 0.5 and 0.7 of the expected remaining life; this time frame for the analysis is NOT related to the inspection intervals in any mitigation strategy.
3.3.3
Regulatory requirements
3.3.3.1
Description
Scope of this step is the collection of all regulatory requirements that could influence the inspection and/or maintenance of the components within the defined boundaries.
3.3.4
Engineering criteria
3.3.4.1
Description
Acceptance criteria are used to compare the results from the risk assessment in order to determine if a scenario is acceptable. 3.3.4.2
Requirements
The team must agree what within the context of their industry is considered a failure of an item of equipment. This activity should be a company issue. 3.3.4.3
Input
Company policy on safety and environment. National legislation as applicable. 3.3.4.4
Warnings, applicability limits
Financial cost elements are best handled on a cost-benefit basis rather than in the form of acceptance criteria. 3.3.4.5
Examples
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Table 3-1 Examples of engineering criteria for determining a failure. Equipment Possible failure criteria Pressure Ves- Localised corrosion leading to leak to atmosphere sel Environmental cracking - no leak Insulation damage/ coating failure - no leak Creep damage to nozzle Heat exchanger Shell localized corrosion leading to leak to atmosphere Internal tube leak from one stream to another
3.3.5
Risk acceptance criteria
3.3.5.1
Description
The metric for risk based decisions should be defined via company standards and/or national legislation. For the process industry in general, three different risk criteria are used: d. Plant worker safety e. 3rd party safety (people outside the plant border) f. Environmental damage, long and short term The above mentioned risk criteria can be expressed in different units, as shown in Table 3-2 below. Some of the units can be derived from another. The different units are more or less well suited for use in conjunction with maintenance planning, but it is beyond the scope to address these issues here. The important aspect is that the overall risk acceptance is adhered to for the local maintenance decisions. The risk acceptance criteria are used to derive the required maintenance activities within the given time frame. For degradation mechanisms developing with time, the degradation rate and acceptance limit provides an upper bound on the time to preventive maintenance or time to inspection. Also the efficiency of an inspection method for detecting degradation and coverage should be considered.
Table 3-2 Risk Criteria. Area Safety
Environment
Name Definition Individual risk (IR) Fatal Accident Rate An average risk for a defined group of (FAR) people. Defined as number of fatalities per 108 working hours. (Typical values: 1-50) Societal Risk (SR) F-N-Curves Defined as number of fatalities and its probability of occurrence. The shape of the graph can incorporate consequence aversion. Volume released per unit time of given substance.
Risk presentation Risk can be presented in different ways, as a time-dependent graph, as a value for the predefined time interval, or as a point in a matrix. Within maintenance planning, risk is best illustrated in a risk matrix. Separate matrices are required for each considered type of risk (safety, health, environment, or economic). Alternatively the scales for different risk types can
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be adapted so that they can be presented in the same matrix. Note also that risk matrices will vary from one plant to another, for example, depending on number of components and the acceptance criteria. The matrices should be standardised adapted for each operator/field to simplify communication and the decision process. To achieve adequate resolution the matrix should not have too few PoF and CoF classes (at least 4 PoF and CoF classes, respectively). Figure 3-2 shows a 5 x 5 risk matrix. The matrix has probability of failure on the vertical axis, and consequence of failure on the horizontal axis. The divisions between the categories of each should be chosen taking into consideration the absolute magnitude of the values, their ranges, and the need for consistent reporting when comparing different plants. For convenience, the risk levels represented by the matrix are divided into zones of equal risk. The zones and thus the boundaries between the zones must be confirmed in relation to the operator’s risk acceptance limits and the local regulator’s limits. One point in the matrix represents one failure event at a given point in time. If logarithmic scales are used on the PoF and CoF axis when developing the matrix, the isorisk curves will be straight lines. It is also possible to use continuous scales on the axis in when developing the risk matrix or plot. Also, a matrix with continuous axis may also be used. In this case the matrix be called a risk plot. The risk acceptance limes should be marked in the risk matrix using the relation (2), further taking into account the part of the risk addressed in the maintenance planning. Cat 5 4 3 2 1
Annual, Probability of Failure -2 expected failure > 10 -3 -2 high 10 -10 -4 -3 medium 10 to 10 -5 -4 low 10 to 10 -5 virtually nil < 10 Consequence category Consequence of Failure
A
B
C
D
E
Figure 3-2 Example of Risk Matrix In order to proceed with a risk based approach like RIMAP procedure, one has to have a clear idea about the acceptability or not of certain risk levels, since every maintenance decision depends on them. The scope of this step is to define risk acceptability (and unacceptability) limits. 3.3.5.2
Requirements
(According to NORSOK standard Z-013: RISK AND EMERGENCY PREPAREDNESS ANALYSIS) Risk acceptance criteria illustrate the overall risk level which is determined as acceptable by the operator/owner, with respect to a defined period of time or a phase of the activity. The acceptance criteria for risk constitute a reference for the evaluation of the need for risk reducing measures and shall therefore be available prior to starting the risk analysis. The risk acceptance criteria shall as far as possible reflect the safety objectives and the particularities of the activity in question. The safety objectives are often ideal and thereby difficult to reflect explicitly. The evaluations that form the basis for the statement of the risk acceptance criteria shall be documented by the operator/owner. Distinct limitations for the use of the risk acceptance criteria shall be formulated. Data that are used during the formulation of quantitative risk acceptance criteria shall be documented. The manner in which the criteria are to be used shall also be specified, particularly with respect to the uncertainty that is inherent in quantitative risk estimates.
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The need for updating of risk acceptance criteria shall be evaluated on a regular basis, as an element of further development and continuous improvement of safety. In order for the risk acceptance criteria to be adequate as support for HSE management decisions, they shall have the following qualities: • be suitable for decisions regarding risk reducing measures. • be suitable for communication. • be unambiguous in their formulation. • be independent of concepts in relation to what is favoured by the risk acceptance criteria. Unambiguous in the present context implies that they shall be formulated in such a way that they do not give unreasonable or unintentional effects with respect to evaluating or expressing of the risk to the activity. Possible problems with ambiguity may be associated with: • imprecise formulation of the risk acceptance criteria, • definition of system limits to what shall be analysed, or • various ways of averaging the risk. Another possible problem is that criteria that are principally different may be aimed at the same type of risk (for example risk to personnel expressed by means of FAR versus impairment risk for main safety functions) may not always give the same ranking of risk in relation to different alternatives. Transport between installations shall be included in the risk levels when this is included in the operations of the installations. The results of risk assessments will always be associated with some uncertainty, which may be linked to the relevance of the data basis, the models used in the estimation, the assumptions, simplifications or expert judgements that are made. Considerable uncertainty will always be attached to whether certain events will occur or not, what will be the immediate effects of such events, and what the consequences will be. This uncertainty is linked to the knowledge and information that is available at the time of the analysis. This uncertainty will be reduced as the development work progresses. The way in which uncertainty in risk estimates shall be treated, shall be defined prior to performing the risk analysis. It is not common to perform a quantitative uncertainty analysis, it will often be impossible. Sensitivity studies are often preferred, whereby the effects on the results from changes to important assumptions and aspects are quantified. The risk estimates shall as far as possible be considered on a 'best estimate' basis, when considered in relation to the risk acceptance criteria, rather than on an optimistic or pessimistic ('worst case') basis. The approach towards the best estimate shall however, be from the conservative side, in particular when the data basis is scarce. 3.3.5.3
Examples
Table 3-3 Individual Risk for public. Authority and Application
VROM, the Netherlands (New plants) VROM, the Netherlands (Existing plants) HSE, UK (Existing hazardous industry) ICRP and NRPB, UK Revision number: 0
Limit of unac- Limit of acceptability ceptability (per (per year) year) 10-6 Not used 10-5
Not used
10-4
10-6
10-4
Not used
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Authority and Application
Limit of unac- Limit of acceptability ceptability (per (per year) year)
(Nuclear industry)
Table 3-4 Individual Risk for Workers. Authority and Application HSE, UK (Existing hazardous industry) ICRP and NRPB, UK (Nuclear industry) Company, Denmark (Continuously manned platform) Company, Denmark (Minimum facilities platform)
Limit of unacceptabil- Limit of acceptity (per year) ability (per year) -3 10 10-6
10-3
Not used
FAR=20
Not used
FAR=40
Not used
Table 3-5 Societal Risk for Public. Authority and Application VROM, the Netherlands (All plants) BS EN 1473 (Onshore liquefied natural gas plants) French Administration (Refrigerating plants using ammonia) API RP 580 (example) (Petrochemical plants)
Limit of unacceptability (per year (slope in for one or log/log presmore fatali- entation) ties)
Limit of acceptability (per year (slope in for one or log/log presmore fatali- entation) ties)
10-3
-2
Not used
Not used
10-6
Not defined
10-12
Not defined
0
Not defined
Not used
Not used
≤ 10-3
Not defined
Not defined
Not defined
Table 3-6 Societal Risk for Workers. Authority and Appli- Limit of unacceptability
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BS EN 1473 (Onshore liquefied natural gas plants) API RP 580 (example) (Petrochemical plants)
3.3.6
(per year for one or more fatalities)
(slope in log/log presentation)
(per year for one or more fatalities)
(slope in log/log presentation)
10-6
Not defined
10-8
Not defined
≤ 10-3
Not defined
Not defined
Not defined
Preliminary Identification of hazards
Note: Preliminary identification of hazards is needed for the Data collection and Validation step. More detailed, Problem and Hazard identification should be conducted when performing multi-level risk assessment, see Chapter XXX 3.3.6.1
Description
The four principal factors contributing to hazards and employee loss exposures include the following: • Human Factors; • Situational Factors; • Environmental Factors; and • Managerial Factors. Each of these four factors is discussed below. Human Factors The human element is one of the most important contributory aspects to the causation and avoidance of accidents. Research concerning causes of industrial accidents indicates that broadly understood human errors, resulting also from organizational inefficiency and management inadequacy, are determining factors in 70-80% of cases (see Kosmowski, 2000). It has been often emphasized in safety related works that disasters arise from a combination of latent and active human errors committed in such areas as design, operations and maintenance (see Kosmowski, 2000). Active human errors refer to an act or failure to act which creates an unsafe condition, which in turn exposes the employee, co-workers and possibly others to an increased probability and potential for an accident. Unsafe acts usually result when standard job procedures are not followed. Some examples of unsafe acts include: • unauthorized equipment operation; • using equipment improperly or at too fast a speed; • operation of equipment or vehicles while chemically or otherwise impaired; • removal of equipment safety guards; • use of defective equipment; • lack of or inadequate training; • lack of or inadequate procedures; • safety measures bypassed; • work pressure or adverse supervisor influence; • poor individual personal attitude toward working safely; • failure to use protective equipment; and, • failure to report hazards.
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Human error may be significantly reduced by implementing correct methods and procedures; training for skill proficiency or equipment use; matching physical ability to job requirements; concentrating on correcting potentially dangerous situations; and by having supervisors correct unsafe actions by employees. The characteristic of latent errors is that they do not immediately degrade functioning of the system, but in combination with other events, which may be active human errors or other random events in the environment, they give together raise to a catastrophic failure. One can distinguish two categories of latent errors: operational and organizational. Typical operational latent errors include maintenance errors, which may make critical systems unavailable or leave the system in a vulnerable state. Organizational latent errors include design errors, which give raise to intrinsically unsafe systems, and management or policy errors, which create conditions that induce active human errors. It is therefore obvious that for a successful identification of hazards there is a need of appropriate techniques for incorporating human factors and associating them directly with the occurrence of accidents, underlying causes or influences. Situational Factors Situational factors also contribute to employee loss exposures. Situational factors include, but are not necessarily limited to: Defects in Design: • unguarded equipment; • poor warning signals; • ungrounded equipment; • lightweight metal; and/or • unvented, combustible flammable materials or containers. Substandard Construction • excessive bearing wear on machines; • ladders with weak rungs; • metal-cast parts with structural faults; • warped metal handles; and/or • missing or ineffective metal connectors. Improper Storage of Hazardous Materials • chemical tanks stored in an unstable manner; • unmarked or unlabeled containers; • unstable storage cans; and/or • separation guidelines not followed. Inadequate Planning, Layout, and Design • aisles too narrow; • lights poorly placed; • welding or painting booth not in protected corner area; and/or, • combustible materials near excessive heat or sparks. Environmental Factors Environmental factors contribute directly or indirectly to potential accident situations. These include the following three areas: • Physical - weather conditions, noise, vibration, lighting, temperature, radiation; • Chemical - chemicals, materials, vapours, fumes, dust, smoke, mist; and,
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•
Biological - molds, viruses, fungi, parasites, bacteria.
Managerial Factors A lack of management commitment and support of the employee safety and health program may produce several factors that weaken safety efforts, such as: • inadequate staffing levels; • inadequate training and education; • improper responsibility assignment; and • failure to maintain equipment and tools that are safe and suitable for the assigned tasks. Understanding the possible combinations and interactions between human, situational, environmental and managerial hazard and accident causation factors helps the agency to identify and eliminate or reduce the causes of occupational hazards and employee loss exposures. 3.3.6.2
Requirements
Employees are in most cases the persons who are closest to potential hazards, and therefore are usually in the best position to identify them. Therefore, an effective communications system must be established for management to encourage input from employees. Hazards and employee loss exposures may be identified by several different methods. These methods may include: checklists, inspections and audits, literature search, surveys, historical accident and claims data, maintenance records, employee suggestions, and safety hazard identification efforts (what-if review, walk through, HAZOP, FMEA). Hazard and loss exposure identification should emphasize, but not necessarily be limited to, the following areas: • housekeeping practices; • condition of equipment; • adequacy of equipment (including personal protective equipment); • use of prescribed equipment (including personal protective equipment); • unsafe working practices; • compliance with policies and procedures; machine guarding; • qualification of drivers; • vehicle condition; maintenance of equipment; • guarding of pits, tanks, and ditches; • storage and handling of chemicals, flammables, and combustibles; • fire extinguishers, first aid, and emergency lighting; • noise and dust levels; • condition of buildings, grounds, streets, and other infrastructure; • incident/accident history; and, • workers’ compensation claims experience. The information collected concerning hazards and employee loss exposures should be analyzed for appropriate recommendations to management for developing and implementing a risk prevention and loss control program. The group carrying out the hazard identification work should include experts in the various appropriate aspects, such as design, operation, maintenance and specialists to assist in the hazard identification process and incorporation of the human element. 3.3.6.3
Input
The identification of hazards has to be related to the defined system boundaries and in accordance with the scope of the RIMAP procedure. The results of both these steps are thus considered as input to the hazard identification step.
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3.3.6.4
Procedure/flowcharts
In general, hazards can be categorized as follows (see Modarres, 1993): • Chemical hazard (e.g., toxic chemicals released from a chemical process) • Biological hazard (e.g., virus released from pharmaceutical industry) • Thermal hazard (e.g., high-energy explosion from a chemical reactor) • Mechanical hazard (e.g., kinetic or potential energy from a moving object) • Electrical hazard (e.g., potential difference, electrical and magnetic fields, electrical shock) • Ionizing radiation (e.g., radiation released from a nuclear plant) • Non-ionizing radiation (e.g., radiation from a microwave oven) The first step in the identification of hazards is thus the recognition of all of the above hazards that may be contained in the defined system boundaries (see Figure 3-3). Category of hazard Chemical hazard Biological hazard Thermal hazard Mechanical hazard Electrical hazard Ionizing radiation Non-ionizing radiation
Recognition of hazards Defined system boundaries Identifiation of barriers that contain the hazards
Identification and analysis of challenges to the barriers
Malfunction of process equipment Wrong operating mode Problems with man-machine interface Poor design or maintenance Adverse natural phenomena Adverse human-made environment
Barrier challenges Strength degradation Increased stress
deformation, abrasion,erosion, cavitation, corrosion, toughness, creep, fatigue, etc. internal forces, elevated temperature and pressure, additional loads due to modified operating modes, collisions, etc.
Figure 3-3 Procedure for the identification of hazards. The next step is the identification of the barriers that contain the hazards. Each of the identified hazards must be examined to determine all the physical barriers that contain it or can intervene to prevent or minimize exposure to the hazard. These barriers may physically surround the hazard (e.g., walls, pipes, valves, fuel clad, structures); they may use distance to minimize exposure to the hazard (e.g., minimize exposure to radioactive materials); or they may provide direct shielding of the subject from the hazard (e.g., protective clothing, bunkers) (Modarres, 1993). The last and most important step is the identification and analysis of the potential challenges to the identified barriers. Of course, one can also try to identify what is needed to maintain the integrity of the barriers. In any case, the approach used for hazard identification generally comprises a combination of both creative and analytical techniques, the aim being to identify as many relevant problems as possible (IMO, 1997). The creative element is to ensure that the process is proactive, and not confined only to hazards that have materialized in the past. It typically consists of structured group reviews aimRevision number: 0
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ing at identifying the causes and effects of accidents and relevant hazards. Consideration of functional failure may assist in this process. The group carrying out such structured reviews should include experts in the various appropriate aspects, such as design, operation, maintenance and specialists to assist in the hazard identification process and incorporation of the human element. A structured group review session may last over a number of days. The analytical element ensures that previous experience is properly taken into account, and typically makes use of background information (for example applicable regulations and codes, available statistical data on accident categories and lists of hazards to personnel, hazardous substances, ignition sources, etc.). A coarse analysis of possible causes and outcomes of each accident category should be made by using standard hazard identification methods (Schlechter, 1995): Literature search, What-if review, Safety audit, Walk through, Checklist, HAZOP, FMEA. The challenges to the barriers that contain the hazards are due to the degradation of their strength and/or high stress in them. Degradation is usually caused by one of the following situations (Modarres, 1993; Schröder and Lecca, 2000): • • • • • • • • 3.3.6.5
Malfunction of process equipment Malfunction of instrumentation and control systems Problems with man-machine interface Manufacturing problems Poor design or maintenance Wrong operating mode Adverse natural phenomena Adverse human-made environment.
Output
The output of this step is a list of identified hazards. These hazards should be considered together with the damage mechanisms that can lead to them in order to establish failure scenarios. Moreover, they have to be considered in the determination of consequences step (sub-step of the multi-level risk analysis).
3.4 Data collection and validation 3.4.1
General
3.4.1.1
Description
The collection and organization of relevant data and information is a mandatory prerequisite to any form of risk based analysis. The data is used to assess both the probability and consequence (risk) of a failure scenario with analysis method(s) that meet the requirements of the generic RIMAP procedure. The quality of the data that is available will vary greatly across industries. Where the data is sparse or of poor quality, the uncertainty associated with the risk assessment will be greater. This will be reflected in the probability and consequence that is assigned to a failure scenario. The data should be collated, verified and stored in a logical database. This will not only facilitate the assessment process itself but also the updating and auditing process that are an essential part of the RBI process. 3.4.1.2
Requirements
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Table 3-7 Information requirements. Inspection Screening Drawings Equipment design Operating and design conditions Operating window (including factors which can be influenced by the operation and factors that cannot be influenced by operation) Upset conditions Susceptibility windows of degradation mechanisms Maintenance and inspection history (incl. current √ equipment state) Experience with similar equipment √ Generic/world data √ National/international regulations and codes √ Layout drawings P&ID √ PFD √ QRA, Safety case √ System description √
3.4.2
Design, manufacturing, construction data
3.4.2.1
Description
Detailed assessment √ √ √ √ √ √ √ √ √ √ √ √ √ √ √
Simplified/schematic process flow diagrams or operating schemes in order help a pressure containment boundary. The degree of detail that is required will correspond to size of the containment boundaries. The data required includes: • • • • • •
Original construction code / national standard. Material of construction/ designation Quality assurance/control and testing carried out during fabrication/ manufacture Original Design envelope General and detailed process/operating description Identifiable major hazards/ HSE concerns
3.4.3
Operating and equipment history
3.4.3.1
Description
Review of the operating and equipment history is a key step for any RB assessment. Where there is no history this increases the uncertainty and hence the probability of failure that is used in the assessment. • • • •
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Details of service / operating history Operating environment/ record of major upsets. Maintenance and inspection history. Details of repairs modification, changes to service / duty.
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3.4.4
Generic/equivalent data
3.4.4.1
Description
One of the biggest problems in estimating the probability of failure of a component – or even worse, the probability of a given scenario – is the usual lack of sufficient data. To overcome this problem, many companies have co-operated to collect data from plant experience for a defined group of components. This type of data is usually called "generic" or "world" data. A number of databases are available; OREDA, IEEE, RAC, T-Book. The standard ISO 14224 ("Petroleum and natural gas industries - Collection and exchange of reliability and maintenance data for equipment") is developed for use when collecting such data. Most of the generic databases are based on the assumption that the failure rate is shaped as a "bath-tub" over a component’s lifetime and is divided in three parts, a burn-in, a useful-life and a wear-out phase. The failure rate is constant during the useful-life phase. If the failure rate is constant, the time to failure is exponentially distributed. In the generic databases, the failure rate is usually presented and estimated as λ = n f / t , where nf is the number of observed failures and t is the total operating (or calendar) time. The mean time to failure, MTTF, is then given by MTTF = 1 / λ . One problem in the data collection is the quality of such generic databases – or lack of collection of information related to the inspection and maintenance as well as operating conditions for a component. Thus, these data should be used with care, and qualified for use in each case. Their applicability depends greatly on several parameters (see Table 3-8)
Table 3-8 Component failure database considerations. Conditions Affecting Component Failure Rates Industry (same or similar) Process fluid (including chemical control) Type of plant (size and fuel type) Manufacturer Inspection sys- Geographic area (environment and extem/program/techniques ternal influences) Unique control, process, design, etc. Operation parameters (pressure, vi- Within the same plant/system/train bration, etc.) Operating environment (moisture, Size, rating, model, design. etc. temperature, etc.) Operating constraints (load following vs. steady state) This means that in order to obtain a reasonable probability (or likelihood) one has to modify the generic data (i.e. to calculate equivalent data) by taking into account all conditions prevailing to the specific problem of interest. (For more information on these issues please refer to the reports of WP3.)
3.5 Multilevel risk analysis and decision making Note: this being one of the most important steps in the analysis is described in more detail in Chapter 4.
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3.5.1
General
3.5.1.1
Description
For any risk analysis task, risk is understood as a measure of the potential negative consequences. With this measure one can then make comparisons, which is an essential part of any decision making (optimization) activity, which is in its turn the reason and goal of any analysis. In the current RBMI practice, risk is considered to be the result of consequences and their respective probabilities. API methodology is calculating risk as the weighted sum of consequences, where the weights equal their respective probabilities. Although this is not the only way to define risk, it divides the problem of risk evaluation in two simpler ones: The identification of all potential consequences and the determination of their probabilities. At this point, a serious methodological problem arises. To proceed with the solution of the above mentioned problems there is a need of data that in most cases are partly known or even unknown. In other words, there is a lot of uncertainty. Moreover, information gathering is not for free since it costs at least time and effort. The proposed solution to this kind of problems is to proceed with a level approach. The level approach The philosophy of the level approach is very simple and intuitive. At a first stage, usually called screening, one makes rough estimates of the consequences and their probabilities. In an RBMI process, the alternatives of the risk analysis can be components and with this screening procedure one can prioritize among them. In the next stage, and based on the priorities derived from screening, one can decide about the problem of gathering or not more data for a specific component, the kind of data to gather, etc. Candidates for a more detailed analysis are thus components that were highly ranked. To avoid overlooking of a component that is not ranked very high but could eventually have a very serious consequence of a certain type (e.g. on economy, safety, etc.) one can even flag these components so as to consider them too. Multi-level approach It is obvious, that if there exists a strict regulation determining the inspection of a certain component, there is not even a need for screening let alone for a detailed analysis. This clearly shows that we can not consider the level approach separately from the actual decision making options. In other words, the benefit of going into a more detailed analysis of a particular component has to be correlated with the inspection (or more generally, maintenance) options for this component. This is only possible if we already have knowledge about the possible inspection methods we could use in each case, i.e. for each component. In case this is not possible, we can only use a traditional level approach. Therefore, for the needs of the new approach, this knowledge is assumed as known. The first issue that this new approach reconsiders is the notion of uncertainty, and particularly the modeling of the uncertainty. Instead of looking for rough estimates of the consequences and their probabilities, one also has to model the uncertainty of the estimates by giving a lower and an upper bound of them. The first stage is then performed as before, only it gives no point estimates for risk but areas (i.e. in a risk matrix, every component is represented by an area). The next step, the determination of the required level (depth, detail) of the analysis, is now much easier to grasp. One has to compare the inspection (maintenance) options corresponding to the best and worst case of each component and act accordingly: In case there is no or little difference a more detailed analysis can not be justified. In case of a clear difference, one Revision number: 0
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can concentrate on first collecting this kind of data that could reduce the part of the uncertainty that most contributes on this difference, e.g. the uncertainty in the estimation of the consequence or in the estimation of its probability. The level of the analysis is therefore component dependent and we can speak of a multi-level approach. Although, the above mentioned approach looks very promising, there is an inherent difficulty, namely the correlation of the risk level of a component with a predefined set of inspection (maintenance) options. However, since the inspection options are correlated with the general condition of a component, the risk level has to be correlated with the general condition of the component. With the later development of the damage mechanism analysis modules we expect that this correlation will be greatly facilitated.
3.5.2
Risk screening
3.5.2.1
Description
The purpose of the risk screening is to prioritise work by reducing work effort on low risk items and increasing the effort on the high risk items. The risk screening will divide the systems and groups of equipment into two groups: high risk items and medium/low risk items. The high risk items require the detailed analysis described in section 3.5.3. The low/medium risk items only require minimal surveillance to verify and ensure that the assumptions made during the screening process remain true. This could for example amount to verify the condition of the coating. Risk screening is a team effort. It is therefore essential that the competencies in section 3.3.1.2 are present during the screening. The risk screening requires 1-2 days work for a process system consisting of approximately 30.000 tags (valves, instruments, pieces of piping) or about 500 maintainable items. The workflow for risk screening is given in Figure 3-4.
RBMI Risk Screening
Systems and Components in SoW
Y
Risk Screening Session -POF -COF - Risk
Plant knowledge Degradation knowledge
Risk Acceptable
N
?
Lack of key Info Minimum Surveilance
Detailed Assessment
Figure 3-4 Risk screening. Revision number: 0
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If information is missing during the screening such that the risk associated with the equipment cannot be determined, the equipment should be regarded to have a high risk and reassessed during the detailed assessment in section 3.5.3. Risk screening consists of the following steps: • • • • 3.5.2.2
Requirements • •
•
•
• • •
3.5.2.3
Identify hazards. Determine likelihood / probability of failure. Determine consequence of failure. Determine risk and classify equipment as high, medium ,or low risk. Rating criteria must be defined and recorded in writing. The likelihood/probability must be established for a given (predefined) time frame based on a prediction of damage development for operation within specified operating window. The specified operating window should include both factors which can be influenced by the operation of the process (e.g. temperature, pressure) as well as factors which cannot be influenced by the operation (e.g. composition of the process medium). The results from the Risk screening must be conservative compared to those from a Detailed analysis. One option to demonstrate conservatism is by executing both types of analysis for a certain number of components, e.g. 10% selection at random. In order to assess the Consequence, at least the aspects Safety, Health and Environment must be included. In addition, the Consequence rating must be such that the highest rating for one of the individual aspects (Safety, Health, Environment and/or financial consequences) must control the final score (so no averaging of aspects). The methodology must be validated. This task should be performed by RBMI team (see preparatory analysis). The results should be auditable to similar experts (peer review); therefore, the methodology, the input data, the decision criteria and the results must be documented (the results must be recorded in an authorized document).
Input
The following information is needed: Identify hazards •
Input from preparatory analysis
Determine likelihood / probability of failure • • •
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The predefined time frame (from preparatory analysis) Maintenance and inspection history of the item of equipment under consideration. Specification of the operating window including both factors which can be influenced by the operation of the process (e.g. temperature, pressure) as well as factors which cannot be influenced by the operation (e.g. composition of the process medium). Page 34 of 135
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• • •
Inspection data on the damage development so far Experience with similar equipment, e.g. average probability data from a relevant database. A methodology that defines rating criteria.
Determine consequence of failure • • •
•
• • •
The composition of the contained fluid and its physical/chemical properties The pressure, temperature and total amount of fluid available of release A methodology that defines rating criteria, at least aimed at the impact on Health, Safety and Environment. If no further input data are used (than the abovementioned data), the criteria must result into a conservative rating compared to a more detailed analysis. Depending on national regulations more data, e.g. the final phase of the fluid on release into the atmosphere, the dispersal characteristics of the fluid at the site, mitigation systems such as water curtains, measures for detection of the leak/break. If it is desired to include the potential leak/break area then the failure mode and the pipe/vessel size must be entered. If it is desired to include business impact then the financial effect of production loss as well as repair/replacement costs must be entered. If it is desired to include publicity damage then a financial value must be entered expressing the negative effect on future business.
Determine risk and classify equipment • 3.5.2.4
Risk acceptance criteria (input from preparatory analysis)
Procedure/flowcharts
Identify relevant hazards The purpose of this task is to identify the relevant hazards for each system within the boundaries of the scope of work (SoW). The known operating conditions, upsets, likely excursions, as well as future process conditions should be taken into account when determining if degradation and/or failure is likely to occur. Determine likelihood / probability of failure For each hazard identified in each system, the PoF should be assessed. The PoF should be determined for the pre-defined time frame. The estimate should be conservative and based on the available information and expert judgement. When the PoF has been determined, it should be assessed whether the PoF is high or low. This amounts to determining whether the PoF is higher or lower than a predefined limit. If this is difficult set PoF equal to 1 and perform a consequence screening. Determine CoF The worst possible outcome of a failure should be established. The safety, health, environment, and economic consequences shall be considered. Other consequences as quality of production and business may also be included. When the CoF has been assessed it should be decided whether it is high or low, depending on whether the CoF is above or below a predefined limit. Possible limits are • Revision number: 0
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• •
Environmental consequence: Release of toxic substances. Economic consequence: any failure leading to production stoppage.
Determine risk and classify equipment Based on the hazard identification, PoF assessment, and CoF assessment, the equipment should be grouped into high and low risk systems or groups of equipment. PoF and CoF should be presented / expressed not only as a combined risk value or category but also separately. Based on the screening results the systems or groups of equipment should be given a low, medium or high risk. Systems or groups of equipment with a high risk should be considered during the detailed assessment. Systems of groups of equipment that have medium risk should be considered for maintenance. Finally, for the low risk systems or groups of equipment the assumptions should be periodically checked. This may amount to verifying that the basic assumptions are satisfied, e.g. coating is satisfactory or that the operating conditions remain unchanged. For low risk systems minimum surveillance is required. Medium and high risk systems should be considered in the detailed analysis. In any case, regulatory requirements should also be taken into account. Figure 3-5 proposes maintenance and inspection activities for systems based on their risk rating. Probability Risk categories and screening High probability Medium risk of failure Maintenance can be used to reduce risk, but is unlikely to be cost-effective; the cheapest solution is often to carry out corrective maintenance upon failure Low probability Low risk of failure Minimum surveillance, with corrective maintenance of failures. Check that assumptions used in the damage assessment remain valid, e.g., due to changes in operating conditions, condition of coating Consequence A Negligible/low consequence
5 4 3 2
1
High risk Detailed analysis of both consequence and probability of failure
Medium risk Consequence is high so inspection and preventive maintenance should be considered to ensure low probability. Apply cost benefit assessment.
B C D E High consequence
Figure 3-5 Screening Risk Matrix The main purpose of the risk screening is to identify the low risk items in category A1 and remove them from further analysis. It is very important that not too many components are placed in category A1. How do we ensure that this does not happen? •
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Ensuring that the acceptance criteria and probability and consequence classes are adapted; and that
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• • 3.5.2.5
limit between low and high probability of failure and consequence of failure are well defined; Ensure that these limits are used during the screening.
Minimal (adequate) measures
For low risk systems (minimal adequate) measures to control the integrity the equipment shall be defined. The purpose is to verify that the assumptions made during the risk screening remain valid. Eventually, it may be concluded not to perform any measures or to minimise the measure allowing a high probability of failure. The measures should be in line with generally accepted industry practice and must meet national regulatory requirements. 3.5.2.6
Output
Typical results from these tasks are: • • 3.5.2.7
A PoF value or category for the piece of equipment under consideration. A CoF value or category for the piece of equipment under consideration
Warnings, applicability limits
Note that PoF assessment usually requires more detail and is therefore more cost intensive than CoF assessments. Therefore some prefer to screen systems and groups of components on consequence of failure only. This is also acceptable, even if the example below suggests another type of screening. 3.5.2.8
Tools
In the field of RBI, a number of commercially available methodologies exist, each including a Risk screening module; see RIMAP Report on Current Practice.
3.5.3
Detailed analysis
3.5.3.1
Description
The Detailed analysis is aimed at establishing an inspection programme based on combination of expert opinion and appropriate quantitative analysis set down in writing, e.g. (at least) trending of inspection data. The detailed assessment may require between 2 and 18 man-months for a topside processing system with approximately 30.000 tags (valves, instruments, pieces of piping) or 500 maintainable items. The total work volume depends on to what extent personnel from the plant are involved in the maintenance and inspection planning. It typically takes 2 to 4 months to complete the task. It consists of the following tasks: • • • • • • • 3.5.3.2
Construct equipment hierarchy Identify relevant damage mechanisms and failure modes Determine likelihood / probability of failure Determine consequence of failure Consider conservative inspection / maintenance Assess risk Construct decision logic
Requirements •
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• •
•
•
•
• • •
must be followed. A conservative approach may be the assumption that the complete content of the containment may escape instantaneously. Rating criteria must be defined and recorded in writing. The likelihood/probability must be established for a given (predefined) time frame based on a prediction of damage development for operation within specified operating window. The specified operating window should include both factors which can be influenced by the operation of the process (e.g. temperature, pressure) as well as factors which cannot be influenced by the operation (e.g. composition of the process medium). The assessment of PoF in a detailed analysis must be based on the value of expected residual lifetime as well as a weighing system/factor to take account of the uncertainty of prediction. The prediction of lifetime may result from one of the following options: measured inspection data, a calculation making use of operating conditions, expert opinion. If so desired, specific analysis tools may be used, e.g. probabilistic (safety) analysis and/or fitness for purpose analysis. For all non-trendable degradation mechanisms (degradation mechanisms of which progress can not be monitored properly or which progress can not be predicted properly, e.g. stress corrosion cracking), it should be demonstrated that they are prevented or early detected by means of sufficient measures to be taken (inspection, maintenance, operation). A methodology should be available in which the relation between the effectiveness of measures (type, scope and frequency) and Likelihood / probability of failure is given. In order to assess the Consequence, at least the aspects Safety, Health and Environment must be included. In addition, the Consequence rating must be such that the highest rating for one of the individual aspects (Safety, Health, Environment and/or financial consequences) must control the final score (so no averaging of aspects). The methodology must be validated. The task should be performed by RBMI team (see preparatory analysis). The results should be auditable to similar experts (peer review); therefore, the methodology, the input data, the decision criteria and the results must be documented (the results must be recorded in an authorized document).
3.5.3.3
Input
3.5.3.4
Identify relevant damage mechanisms and failure modes • • • • • •
3.5.3.5
Operating and design conditions Upset conditions Susceptibility windows of degradation mechanisms. Characteristics of potential degradation mechanisms, e.g.: local or overall degradation, possibility of cracking, detectability (in early or final stage). Mechanical loading conditions Geometry of piece of equipment
Determine likelihood / probability of failure
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• •
• •
•
3.5.3.6
The predefined study period (from preparatory analysis). The specified operating window, which should include factors that can be influenced by the operation of the process (e.g. temperature, pressure) and factors that cannot be influenced by the operation (e.g. composition of the process medium). Plant specific experience (data or soft knowledge). The PoF assessment in a detailed analysis must be based on the value of expected residual lifetime as well as a weighing system/factor to take account of the uncertainty of prediction. The prediction of lifetime may result from one of the following options: measured inspection data, a calculation making use of operating conditions, expert opinion. If so desired, specific analysis tools may be used, e.g. probabilistic (safety) analysis and/or fitness for purpose analysis. For all non-trendable degradation mechanisms (degradation mechanisms where progress cannot be properly monitored or properly predicted, e.g. stress corrosion cracking), it should be demonstrated that degradation is prevented or detected early by means of sufficient measures to be taken (inspection, maintenance, operation). A methodology should be available in which the relation between the effectiveness of measures (type, scope and frequency) and probability of failure is given.
Determine consequence of failure
The consequence assessment requires (depending on application) the following input: • •
•
• •
• • •
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Characteristics of the relevant degradation mechanisms, e.g.: local or overall degradation, possibility of cracking, detectability (in early or final stage). If containment is considered, the composition of the contained fluid and its physical/chemical properties, the pressure, temperature and total amount of fluid available of release shall be available. To obtain satisfactory CoF assessments may in this case often require to defining a number of scenarios, e.g., small leakage, large leakage, and full rupture. Characterisation of mitigating systems (water curtains, detection and warning systems, monitoring, etc.) During the safety, health and environmental CoF assessment credit may only be taken for passive mitigating systems. Consequences should also be assessed for hidden failures and test independent failures. Depending on national regulations more data, e.g. the final phase of the fluid on release into the atmosphere, the dispersal characteristics of the fluid at the site, mitigation systems such as water curtains, measures for detection of the leak/break. If it is desired to include the potential leak/break area then the failure mode and the pipe/vessel size must be entered. If it is desired to include business impact then the financial effect of production loss as well as repair/replacement costs must be entered. If it is desired to include publicity damage then a financial value must be entered expressing the negative effect on future business.
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3.5.3.7
Procedure/flowcharts
Detailed Assessment High Risk Components from Screening Functional Hirarcy
Equipment Hirarch System
Components
Subfunctions
Parts Failure Mode
FMEA: Failure Mode Effect Analysis
Consequence of Failure assessment
Risk
Functional Description
Degradation Mechanisms
Probability of failure assessment
Decission Logic. Risk Acceptable, Strategy Cost effective
Corrective Maintenance
Functional Testing
Time based Maintenance
Condition Based Maintenance
Modification of System/ component
Strategy and Maintenance Plan
Figure 3-6 Detailed assessment
3.5.3.8
Construct equipment hierarchy
The purpose of the first step is to, if necessary, divide the system under consideration into its individual components as well as to collect information on process-service/material damage, design, operation history, and damage mechanisms. The level of detailing should be chosen with care to ensure that all the relevant damage mechanisms are considered, at the same time as the scope of work is limited as much as possible. The level of detail also depends on the level of detail required to perform the inspection/maintenance planning as well as the amount and the quality of the available input data. The level of detailing is usually increased for high risk components. The analysis should start at system level and proceed to tag or maintainable item level. To simplify the detailed assessment, it is recommended to define groups of components so that analysis done for one component can be applied to the other components within the same group. Corrosion circuits and pumps operating under similar conditions are examples of component groups. Different component groups can be defined for CoF and PoF assessments. P&ID’s and PFD can for example be used to document the picture.
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A number of tools can be used for identifying hazards. In this case it is recommended to carry out a system level FME(C) analysis. A number of standards for FME(C)A are available: • • •
IEC812 (1985) Analysis techniques for system reliability – Procedure for failure mode and effects analysis (FMEA) MIL-STD-1629A (1980) Procedures for performing failure mode, effects and criticality analysis. etc.
There are also a number of software tools that can support FMECA analyses. 3.5.3.9
Identify relevant damage mechanisms and failure modes
The purpose of this task is to identify the relevant degradation mechanisms and failure modes. This is a group activity that requires that the competencies in section 3.3.1.2 are present or can be consulted. A number of techniques can be used to identify the hazards. We recommend that a FME(C) analysis is applied, but HAZOP, HAZID, Check-lists, FMEA, FMECE, Check-lists, or What-if analysis, or experience from similar facilities can also be used alone or to supplement the FME(C)A . If previous analyses exist, the results from these can be used as input in to this task. The information identified in Table 3-7 shall be available during the identification damage mechanisms and failure modes. 3.5.3.10
Determine probability of failure
The current probability of failure and the PoF development over time shall be assessed for all relevant degradation mechanisms. The development of the PoF over time is an important parameter to consider when the maintenance/inspection strategies and intervals are determined later in the analysis. The probability of failure shall also be linked to the appropriate end event in the bow tie model to ensure that each consequence is assigned the correct probability of failure. In addition the uncertainty in the PoF assessment shall be determined. The methodology specifies the criteria and numerical routines which take into account the following factors: • • • • • •
3.5.3.11
the relevant degradation mechanisms loading by the future operating conditions compared by the past operating conditions the impact of operating conditions on the susceptibility of the potential degradation mechanisms (both the probability of initiation and the effect on progress) calibrate the PoF model with inspection data or past experience. The damage development based on extrapolation of inspection data from past. Combination of the individual PoF ratings for each potential degradation mechanism to an integrated value or category for the piece of equipment under consideration.
Determine consequence of failure
The safety, health, environmental and economic consequence of failure (CoF) shall be assessed for the relevant degradation mechanisms. Other consequences, e.g., to quality of the product or business risk, may also be considered. Note that the risk is usually not reduced by mitigating the consequences, but by mitigating the PoF. Scenarios (sequence of events) and event trees shall be established to enhance the accuracy of the consequence assessment Revision number: 0
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for serious events. The event tree must be developed or adapted to the particular application at hand. Event trees can be found in QRA’s, safety cases, or published literature. The consequence of failure shall also be linked to the appropriate end cause in the bow tie model to ensure that each end event is assigned the correct probability of occurring. This is only done for the most reasonable scenarios. In addition the uncertainty in the CoF assessments shall be determined. 3.5.3.12
Consider conservative inspection/maintenance
Conservative inspection/maintenance is an efficient method for defining an inspection and/or maintenance program, if the mitigating actions are cheap compared to developing an optimised maintenance/inspection plan. Conservative maintenance/inspection programs are obtained using conservative PoF and CoF assessments, that require little work effort, as a basis for defining the mitigating activities. Uncertainties in the analysis shall be assessed. The information listed in Table 3-7 is required for developing a conservative maintenance/inspection plan. Note that developing a conservative inspection/maintenance program places particular responsibility on the personnel involved and their competencies, see section 3.3.1.2, to ensure that the risk is acceptable after conservative inspection has been carried out. It consists of the following steps: • • •
Select the highest level of effectiveness for inspection. Calculate the resulting PoF taking account of eventually demonstrated degradation. Check whether the resulting mitigated Risk is acceptable taking into account the CoF level from the Risk screening.
The output from this task should be a highly effective inspection programme. 3.5.3.13
Risk assessment
When the PoF and CoF has been assessed, the safety, health, environment, and economic risks and economic risks shall be determined. The results can be plotted in risk matrices for presentation and comparison. Separate matrices should be used for each risk type unless it is relevant to compare the risk types Note that the risk matrix presents the risk for a predefined time period. If the risk for other time periods or the development of risk over time is of interest, additional risk matrices should be used. The risk results should be compared with other related studies if available, e.g., QRA’s and safety cases. 3.5.3.14
Decision logic
If the risk is found to be unacceptable (compared with the objectives defined in Section 6.2.1) mitigating strategies shall be defined. The decision logic is a structured method for deriving maintenance and inspection strategies. Figure 3-7 illustrates an example of a decision logic. It is not compulsory to use the decision logic to derive maintenance strategies. Note that the first column in the decision logic addresses some aspects that are also addressed in Table 3-9.
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Cause, Criticality and Cost Efficiency 1 Can failure cause be cheaply identified and is elimination clearly cost effective?
5 Is operational Y maintenance applicable and effective?
Y
N
3 Is failure risk low for production and follow cost?
Y
Y
Strategy 11 Implement: procedure modification operating condition
Y
Y 2 Is failure risk low for safety and environment?
Failure Characteristics
Failure Detectabilty
Operational Maintenance
N
7 Is failure mechanisms/ cause known and detectable to Operator Technician/ Responsible Person?
N
8 Is development of failure machanism dectable by: y NDT y Installed CM methods y Analysis of process data
4 Is PM more cost effective than CM?
Y
12 Regular funcitonal testing/inspection
Y
13 Time based maintenance (running hours or calander based PM)
N 10 Has component predictable age?
Y
Y 6 Does Operational Maintenance filfill requirements for preventive maintenance?
N
9 Can hidden failure be det-ected by sched-uled tests or inspection?
N N
Y
NDT
Y
N PM: Preventive Maintenance CM: Corrective Maintenance NDT: Non Destructive Testing/Inspection
14 Implement: - modification - oper.procedure - task combination 15 Condition based Maintenance
16 Inspection/NDT 17 Operational Maintenance 18 Corrective Maintenance, Run to failure.
Figure 3-7 Decision Logic. Some typical examples illustrating the application of the decision logic are presented below:
Table 3-9 Examples of decision logic application. Case Decision route Corrosion under insulation for Screened as high risk. a pipe 1 to 11 in case less expensive painting can be done 1, 2, 5, 7, 8, 16. I.e. Regular Inspection Stress corrosion cracking of a 1, 2, 5, 7, 9, 12: Testing/inspection pressure vessel 1, 2, 5, 7, 9, 10, 14: No inspection possible Maintenance of a gas de- 1, 2, 5, 7, 9, 12: I.e. regular testing of function at tector given intervals. Intervals to be set by reliability requirements. Maintenance of a bearing of 1, 2, 3, 5, 7, 8, 15: Failures can be detected by a rolling mill CM and scheduled accordingly. When the maintenance/inspection strategy has been determined, the method, intervals, and extent of inspection must be determined such that risks remain acceptable and costs are optimised. This is achieved by establishing risk reduction measures for each maintainable item. The risk reduction effect of alternative measures as well as the costs of these measures
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should be determined. The method should be chosen based on cost optimisation subject to the boundary condition that the safety, health, and environmental risks satisfy the acceptance criteria defined in section 3.3.4. 3.5.3.15
Output
Typical results from these tasks are: • • 3.5.3.16
A PoF value or category for the piece of equipment under consideration. A CoF value or category for the piece of equipment under consideration
Warnings, applicability limits
Not Applicable 3.5.3.17
Tools
In the field of RBI, a number of commercially available methodologies exist, each including a detailed analysis module; see RIMAP Report on Current Practice.
3.5.4
Multilevel analysis
3.5.4.1
Examples
E/J
Expert Judgment
E/J
PoF’ Basic PoF/LoF estimate
Direct Input
Expert’s Correction
PoF/LoF
Statistical analysis of Historical data
F/M
Data: failures, operation, loads, materials, geometry, plants, inspection…
Input
Prediction of possible Future behavior based on analytical and other Models
Input
Input
H/S
Figure 3-8 Example of PoF (LoF) calculation.
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Plant Plant
Cause 1 Yes
AN D Cause 2 AND
System System
Cause 3 OR
Component Component
Cause 4
PROBLEM / PROBLEM / ISSUE ISSUE Bow tie Failure Bow tie “Scenario” “Scenario”
E E1
E E2
E E3
E E4
PROBLEM / PROBLEM ISSUE #1 / ISSUE #1 Scenario Scenario Damage mechanism - fatigue Consequence evaluation - health & safety - environment - economics
Modules, tools - fatigue - creep - failure
PROBLEM / PROBLEM ISSUE #2 / ISSUE #2 Scenario Scenario Damage mechanism - creep
Consequence evaluation - health & safety - environment - economics
Modules, tools - health & safety - environment - economics
Figure 3-9 Example of PoF (LoF) issues in practice (power plant).
3.6 Implementation of plans 3.6.1
General
RIMAP Risk Based Inspection and Maintenance planning considers two phases in the Inspection and Maintenance planning: Phase 1: Development of the I&M plan, and Phase 2: Execution of the I&M plan.
3.6.2
Development of the I&M plan
3.6.2.1
Description
Determine the (cost) effective inspection and maintenance strategy based on the Risk Analysis (PoF x Consequence) for each failure mode per maintainable item to achieve the desired Risk Level. A maintainable item can either be a system, equipment or component. The level of detail for the maintainable item is preferably in line with the actual situation how inspection and maintenance teams keep track of data for their activities and history data logging based on sound practice. To be able to develop an effective I&M plan a structured approach is needed for required input, experts to consult and for output.
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The combination and cooperation of experts contributes highly to the quality and capability of the I&M plan. The input needs will include but is not limited to the following areas of expertise: Risk (PoF x Consequence) but also input from Operation, Process, Maintenance, Historical Data and Design input. The output of an I&M plan is the input for the planning and scheduling for all involved departments, disciplines and contractors of the inspection and maintenance work for the facility and its maintainable items. The output of the development of the I&M plan will be based around a maintainable item and will have a broad variety of strategies such as the elimination of the risk or item, monitoring, performance testing, improvement of procedures for process, operation and/or maintenance, inspection, modification, repair, replacement, or operate to failure. 3.6.2.2
Requirements
Knowledge and Experience The development of the I&M plan will be done by a team or person meeting the following qualifications: • • •
Sufficient knowledge of Risk levels, PoF and Consequences and qualified knowledge of the Maintainable items considered. Experience with the facility and the maintainable items to inspect. Generally several years of familiarity with the operation and maintenance of the facility is required. Access to all relevant data and Risk Analysis. More details are mentioned in the paragraph: Inputs.
Input The actual Risk Level and the Desired Risk level. For details see paragraph: Inputs. Output The output should be presented in a way that the planning and scheduling of inspection and maintenance activities can be achieved and fits in the company’s procedures for the execution by all departments, disciplines and contractors. Tracebility The I&M plan will be uniquely related to the maintainable item(s), originator and will be dated. Risk level relation The I&M plan will contain all relevant details on the strategy level for execution in order to obtain the desired reduction of level of Risk as set by the RBMI analysis and process. Actuality The I&M plan will be reviewed and updated directly after inspection and maintenance are executed for effectiveness, completeness and future use of the I&M plan. 3.6.2.3
Input
Desired Risk level by:
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•
Risk information out of the RBMI analysis (PoF and Consequence). PoF is particularly important for Inspection and Maintenance information at the level of a maintainable item such as: Degradation mechanism Failure mode Trendable or Non trendable failure development Actual Risk Level by: • Inspection and Maintenance data Historical data on damage and deterioration and its associated failure analysis, including details of causes and actions to resolve, to prevent, to predict and/or to monitor. Historical data on inspection, tests and trends thereof. Historical data on executed repairs, replacements, modifications. • Actual general verification of condition (“so called pre-inspection”) Field examination for information and verification of the actual status of the Maintainable item (System, equipment or component) by visual inspection and obvious to do NDT organized and/or executed by a qualified inspector. • Design Condition Design conditions on the level of the Maintainable item (System, equipment or component) such as: Specifications (materials, welding ) Drawings (dimensions, construction ) Procedures (installation-, operation- and maintenance instructions) Manufacturing data (actual data on used materials, welding details, examinations and tests performed) • Process data Information of process data such as: Product specifications Product variability Out of specification product events • Operation data Information of operation data such as: Normal Operation window, design criteria (temperature, pressure, flow) Deviation of normal window of operation, consequences and investigations thereof. • Outside influences Extreme atmospheric conditions e.g. severe storms, flooding, land slides, land sinks, tornados, hurricanes, earth quakes. Extreme surrounding conditions e.g. fires, pressure waves, explosions, deflagration, and detonation. 3.6.2.4
Procedure/flowcharts
Gather Input data Field examination (pre-inspection) Development phase of strategies by study of inputs and field examination Output generation of strategies per maintainable item 3.6.2.5
Output
Strategy per maintainable item Revision number: 0
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The output of development of the I&M plan will be a strategy per maintainable item to achieve the desired Risk Level. The type of output to be considered for an item will be one of the following possibilities. Typically the following sequence represents the order of preferred solutions: a. Elimination or minimization of the risk (by obvious change, replacement if possible) b. Condition based inspection and maintenance e.g. NDT plan or monitoring c. Time based inspection and or maintenance, calendar or operation time based e.g. NDT plan, lubrication etc. d. Regular performance testing (e.g. for hidden failures, typical for protective devices and instruments) e. Modification of procedures and/or improvement of discipline (human factor) for process, operation and/or maintenance. f. Corrective maintenance e.g. operate to failure g. Repair, Modification or Replacement of item 3.6.2.6
Warnings, applicability limits
Inputs for generation of an I&M plan are broad in variety. The quality and capability of the output of an I&M plan highly depends on these inputs. The inspector in charge or depending the organization structure the management for the development of the Inspection and Maintenance plan plays a key role. The way the entire organization is able to achieve the full cooperation and support of the functions operation, process, maintenance and other experts to detail the item characteristics, highly influences the quality and capability in the development phase the execution of the plan.
3.6.3
Examples
Expert systems like DMI. Dialog Modular Inspection Plans. DMI is a program to build a company’s Expert System for Inspection plans by sequence of process function, type of maintainable item and type of strategy. DMI guides inspection experts through most relevant questions on the maintainable item while in the meantime the program is generating the inspection and maintenance plan for the item.
3.6.4
Execution of the I&M plan
3.6.4.1
Description
Execute the activities for the maintainable item in the inspection and maintenance plan to achieve the desired Risk Level. Per maintainable item (system, equipment or component) the actions with the skill levels required and resources needed will be planned and scheduled. These actions will be processed as work-orders to the inspection and maintenance crews internally or to service-contractors. Evident failures, deviations or deterioration’s found during the execution of the actions need to be addressed to the responsible inspector and maintenance team for follow-up action. The follow-up action will vary in nature such as: a. b. c. d.
Immediate action e.g. repair, replacement Future action e.g. planned repairs, planned replacements Review of data for updated (future) strategy Address lack of Risk reduction against the Desired Risk Level to the responsible organization.
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The primary objective of the Execution of the I&M plan will be to achieve the new acceptable level of Risk (PoF x Consequence). In most cases only the PoF level will be reduced to achieve the new Risk Level. Typically the Consequence will not be influenced. The Consequence is often inherent to the concept of design. Where a sufficient Risk reduction is not achieved future actions or reviews should be addressed to the organization for follow-up action. 3.6.4.2
Requirements
The execution of the I&M detailed activities will be done by: a. Skilled and trained people For each skill an education, experience and qualification level should be defined. Measurements will be the main output of the I&M plan detailed activities. On the basis of the measurements the Qualified Inspector will inspect against criteria set by RBMI and design conditions. In cases where assessments have to be made outside the competence of the Qualified Inspector, the Qualified Inspector will inform and organize the experts needed for full assessment of the findings and measurements. The experts may be from different disciplines: Design Engineering, Operation, Process Engineering, Maintenance, Material- or NDT specialists or Outside Experts where deemed necessary by the Qualified Inspector. 3.6.4.3
Input
Detailed I&M actions out of the development phase of the I&M plan by skill and needed resources. Immediate actions e.g. extended measurements, tests, repairs, modifications and replacements based on inspection findings and data under the responsibility of the Qualified Inspector. 3.6.4.4
Procedure/flowcharts a. b. c. d. e. f.
3.6.4.5
Execute detailed I&M activities Perform comparison of I&M results with Design Conditions Make assessment of possible gaps. Fix the obvious by immediate actions Assure the compliance and sufficient Risk reduction is achieved. Review the data and update the strategy on maintainable item level for future use. Address the future actions and/or reviews for follow-up action where sufficient Risk reduction is not immediately achievable.
Output
Documented inspection findings, measurements and data. Depending on the situation: a. b. c. d. e. f.
Documented inspection measurements, findings, trends and results Documented performance tests Documented repair Documented modification Documented replacement Updated Operation and Process plan
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g. h. i. j.
Updated I&M plan Future actions needed for planned repairs, replacements Reviews of data needed for update of (future) strategy with experts Address lack of sufficient Risk reduction to organization for follow-up action
3.7 Evaluation of the process 3.7.1
Description
The purpose of the Evaluation of the risk-based decision-making process is to assess its effectiveness, its efficiency and its impact in the establishing of inspection and maintenance programmes. This will allow the identification of areas where modifications and improvements are needed. Specifically, Evaluation consists of the following tasks: Task 1: Assessment of the effectiveness of the risk decision-making process at achieving the intended goals (Assessment of Effectiveness) Task 2: Updating the risk decision-making process by taking into account of possible plant changes and available new knowledge (Reassessment of the Risk).
3.7.2
Requirements
The Evaluation process involves both internal and external assessment conducted by the operating organisation and by independent external experts, respectively. The internal evaluation by the plant organisation is an integral part of RBMI activity and should be considered as a living process within the overall risk decision-making process. Internal evaluation can take place in any moment of RBMI, especially when: a. discrepancy from expectation is found (Task 1) b. new knowledge is available or plant changes occur (Task 2) In both cases, a detailed analysis of the importance of the involved item (discrepancy or new knowledge/plant change) has to be conducted in order to assess whether it has a significant impact on the RBMI process and some corrective actions should be undertaken. In these cases a thorough analysis of the discrepancy causes or the new knowledge/plant changes effects have to be performed. External evaluation can be executed through independent reviews by external or regulatory organisations (e.g., audits). Independent reviews provide an opportunity to complement the internal evaluation with a different and neutral perspective. A point to note is that the value of information provided by the independent review is directly proportional to the openness and collaborative environment that external experts will find in the audited organisation. The integration of independent reviews with internal evaluation will allow the identification of necessary actions for improvement.
3.7.3
Input
3.7.3.1
Assessment of effectiveness a. Definition of risk decision-making process goals. (Risk may be expressed in one or more of the following terms: safety, health, environment and business impact) b. Definition of Performance Indicators as a measure of the RBMI process achievements against the above goals. (Note that in order to enable a meaningful evaluation of the performance, consideration should be given to the appropriate time frame applied for the various performance indicators. Especially when a relation should be identified between the performance and potential causes, it may be more meaningful when certain quantities are
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assessed for a longer period of time. For example, the cost of inspection and maintenance in year X has effect on the availability in a certain period of time after year X.) c. Reference to existing standards. d. Benchmarking with similar operating organisations. 3.7.3.2
Reassessment of risk
Plant Information: • • • • • • • • New Knowledge: • • • • • •
Design changes Plant operating changes (mission, operational regime, production rate, capacity, internal & external environment) Time dependent operating conditions (e.g., fatigue, cracks) Plant Management changes Level of personnel’s training change Industry wide operation experience feedback Inspection results (degradation rate of relevant degradation mechanisms) Maintenance records Applicable research and development results Newly improved risk processes Advanced Inspection Methods Failure data Newly degradation mechanisms (absence / presence of unanticipated degradation mechanisms) Newly data on inspection and testing effectiveness
3.7.4
Procedure/flowchart
3.7.4.1
Assessment of effectiveness
This task can be fully exploited after defining the main goals of the risk-decision making process and proper performance indicators to assess its effectiveness. The mentioned goals and corresponding performance indicators are plant specific and depend upon the specific risk based application considered. For instance, if risk assessment is focussed on economics, a possible performance indicator to assess the effectiveness of the risk decision-making process is the effective cost reduction for the implementation of plant inspections and/or maintenance, which is achieved by maintaining a similar level for safety. 3.7.4.2
Reassessment of risk
This task corresponds to the feedback activity based upon the re-assessment of risk when plant changes affecting failure probabilities or failure consequences occur. These changes could be due to: design changes, plant operating changes, time dependent operating conditions (e.g., fatigue), industry wide operation experience feedback, inspection results, etc.). The affected portions of the risk based inspection and maintenance programmes shall be reevaluated as new knowledge affecting implementation of the programme becomes available. For instance if a new degradation mechanism is discovered, the whole risk ranking must be re-evaluated and the inspection and maintenance planning should vary accordingly. This dynamic or living process is one of the strengths of the risk based decision-making logic. It leads to an enabling process that is both flexible and responsive to emerging problems.
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Figure 3-10 Evaluation of the risk-based decision making process. 3.7.5
Output
3.7.5.1
Assessment of effectiveness • • • • •
3.7.5.2
Reassessment of risk • • • • •
3.7.6
Periodical reports from internal reviews Reports from external audits List of discrepancies from expectations Methodical analysis of discrepancy causes, when applicable Proposal for improvement actions Periodical reports from internal reviews Reports from external audits Monitoring and feedback from operation Feedback from new knowledge Proposal for improvement actions
Warnings, applicability limits
Modifications in the process as well as modifications and/or repairs to the installation should be designed and carried out in accordance with a written procedure reflecting appropriate standards and agreed is advance. This procedure must include an evaluation of the possible consequences of the change with respect to the integrity of the installation as well as the way in which authorisation must take place. All information should be included in the plant database and be available to the RBI-team for review.
4. Problem and hazard identification – damage mechanisms, plant hierarchy This chapter considers the systematics, detection and analysis of damage in power plant systems and components subject to RBI/RBLM analysis. It also presents the plant break down or in other words, the component hierarchy that should be used in a power plant. Inno-
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vative moment is shown at the end of this chapter (in Table 4-13) combining the damage systematics with the plant hierarchy, actually giving possible scenarios. The consideration of damage follows the flowchart shown in Figure 4-1.
Components Considered Operating loads
Determine measures in monitoring/inspections/analysis for initial, pre-symptom appearance measures
Damage appeared (symptoms)
Decision which inspection methods according to symptoms
Apply the inspection methods and assess their appropriateness/reliability for the needs of RBI/RBLM
Analyze damage and its possible propagation
Figure 4-1 Damage considerations in this workbook
4.1 Damage Systematics Note: Considering damage mechanisms (including systematics) is explained in detail in PART III – APPENDIX A: Damage mechanisms Based on the different damage mechanisms considered in the approaches of others (e.g. VDI, API)2, a new approach is proposed here. New damage systematics are shown in Table 4-1. These are later combined with the plant hierarchy producing a Problems vs. Components matrix. Example of this matrix is given in Table 4-13.
2
API 581, Risk Based Inspection Base Resource Document, First Edition, May 2000
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Table 4-1 Types of in-service damage and their specifics: Classification adopted in this work. Id. Type of damage Damage specifics MATERIAL DAMAGE RELATED PROBLEMS I. Corrosion/erosion/environment related damage, equating or leading to: I.A1 Volumetric loss of mate- General corrosion, oxidation, erorial on surface (e.g. thin- sion, wear ning) I.A2 Localized (pitting, crevice or galvanic) corrosion Cracking (on surface, Stress corrosion (chloride, caustic, I.B1 mainly) etc.) I.B2 Hydrogen induced damage (incl. blistering and HT hydrogen attack) Corrosion fatigue I.B3 Material weakening Thermal degradation (spheroidiI.C1 and/or embrittlement zation, graphitization, etc. incl. incipient melting) I.C2 Carburization, decarburization, dealloying I.C3 Embrittlement (incl. hardening, strain aging, temper embrittlement, liquid metal embrittlement, etc.) II. Mechanical or thermomechanical loads related, leading to: II.A Wear Sliding wear, cavitational wear II.B Strain / dimensional Overloading, creep, handling damchanges age II.C Microvoid formation Creep, creep-fatigue II.D Microcracking, cracking Fatigue (HCF, LCF), thermal fatigue, (corrosion fatigue), thermal shock, creep, creep-fatigue II.E Fracture Overloading, brittle fracture III.
Other structural damage mechanisms DISTURBANCES / DEVIATIONS / PROBLEMS (not related to structural materials) IV. Fouling / deposits V. Fluid flow disturbances High/Low fluid flow; no fluid flow; other problems with fluid flow VI. Vibration VII. Improper dimensioning , improper clearances VIII. Sabotage, terrorist attack and man made disturbances, fires, explosions, and similar IX. Disturbances and/or loss Break; leak including external leakof function age; improper start or stop; failed while working; overheated; other
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4.1.1
WHERE to look for (inspect / monitor) for which type of damage
Generally, types of damage defined in previous chapter (see 4.1) can be found on a very large number of places in a plant depending on its construction, applied materials, operating conditions, etc. For the purpose of a general overview, data on typical locations in different types of plants are given in Table 4-2.
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Table 4-2 Classification of type of damage vs. systems/components in different types of plants (FPP – fossil power plants, NPP – nuclear power plants, PrP – process plants; weld critical in all components) Type of damage
Where to look for it (typical sample components/materials)
Ide Damage specifics, nType of damage FPP - steam turbine tidamage mechanism fier I. Corrosion/erosion/environment related damage, equating or leading to: I.A1 General corrosion, oxida- boiler and supertion, erosion, wear heater tubing, LP solid particle erosion blading, and shaft pumps, valves Volumetric loss of material on surface (e.g. thinLocalized (pitting, crevice Boiler tubing, heat I.A2 ning) or galvanic) corrosion exchangers, condensers, LP-blades, IP-/ LP-shaft I.B1 Stress corrosion (chlo- steam drums, LP turride, caustic, etc.) bines (disks, blade attachments and blades), bolts I.B2
Cracking mainly)
I.B3
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FPP - gas turbine
blading, com- pump casings, pressor, LP turbine cascombustor ings, condensers, and shaft blading
surface, Hydrogen induced dam- waterwalls age (incl. blistering and HT hydrogen attack) Corrosion fatigue waterwalls, drums, blading dissimilar welds, LPblading
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PrP
Heat exchangers, pipes, bends, pumps, reactor vessels Heat exchangers, reactor vessels, pipes stainless piping, reactor vessels
Heat exchangers, steam generators stainless piping, LP turbines (disks, blade attachments and blades), bolts pressurizer crackers, columns, reformers nozzles, safe- dissimilar welds end, sleeves, LP-blading
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Type of damage Ide ntifier I.C1
Type of damage
Where to look for it (typical sample components/materials) Damage specifics, damage mechanism
FPP - steam turbine
FPP - gas turbine
PrP
heat exchangers, reformers, crackers, pipes, reactor vessels reformers, crackers clad- reactor pres- forgings, hot sure vessel vessels and piping
hot combustors, Thermal degradation superheaters, (spheroidization, graph- headers, steam lines, hot blading, transition itization, etc. incl. incipi- casings, bolts ducts ent melting)
Material weakening Carburization, decarburiand/or embrittlement zation, dealloying I.C3 Embrittlement (incl. forgings, bolts, shafts hardening, strain aging, temper embrittlement, liquid metal embrittlement, etc.) II. Mechanical or thermomechanical loads related, leading to: II.A Wear Sliding wear, cavitational pumps, valves, conwear densers, sealing, blading, bearings II.B Strain / dimensional Overloading, creep, han- hot steam lines, pichanges dling damage ping, T-Y pieces, bored rotors, casings (casing joint plane) II.C Microvoid formation Creep, creep-fatigue hot steam lines (all, incl. welding), headers, bored rotors, I.C2
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disks, ding
blade tips, seals, duct connections blading
hot blading, combustors, transition ducts
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pumps, valves, condensers, bearings fuel rod cladding
pumps, valves, condensers hot piping, nozzles, T-Y pieces hot piping, reformer tubes, reactor vessels
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Type of damage Ide ntifier II.D
II.E
Type of damage Microcracking, cracking
Fracture
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Where to look for it (typical sample components/materials) Damage specifics, damage mechanism
FPP - steam turbine
FPP - gas turbine
NPP
PrP
rotating mathermal sleeves, safe- chinery end. valve internals, valves, turbine shafts and casings vessel failures, Overloading, brittle frac- rotors, retaining rings, blading (for- rotors, disks pipe bursts, ture, foreign object dam- LP blading, super- eign-object reformer tubes age heater tubes, gears, damage), gears disks Fatigue (HCF, LCF), rotors, bolts, welds in thermal fatigue, (corro- heavy-section pipes, sion fatigue), thermal valve internals, turshock, creep, creep- bine shaft and blading, casings fatigue
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4.1.2
HOW to look for (inspect / monitor) for which type of damage
For the decision which method to apply and for inspection and what kind of result with witch level of confidence can be expected, the preliminary data in Table 4-3 can be used. For early discovery of damage, or decision making on where to look for possible damage Table 4-4 can be used.
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Table 4-3 Classification of type of damage vs. prioritized methods of inspection3 How to look for it 4 5
What type of damage Iden tifier
Type of damage
Damage specifics, mechanism
damage
best POD7
I. Corrosion/erosion/environment related damage, equating or leading to: I.A1 Volumetric loss General corrosion, oxidation, DiM, VT, of material on erosion, wear ET, UT8 (e.g. Localized (pitting, crevice or UT, DiM, I.A2 surface thinning) galvanic) corrosion ET I.B1 Cracking corrosion (chloride, MT, PT, (on Stress caustic, etc.) surface, mainly) ET I.B2 Hydrogen induced damage UT, MT, (incl. blistering and HT hydroPT, ET gen attack)
Measure of uncertainty/risk for selected/preferred method6
selec- POD for defect size of or size FCP7; for commost cost ted ments, effective meth 90% 1 mm 3 mm examples od POD UT, (VT), UT DiM VT, UT MT, ET
UT PT,
ET
MT, PT11, UT MT12
3
30÷70 % 30÷70 % 1÷85% na
50÷90 % 40÷90 % 40÷90 % na
2 mm 2 mm
see 9
4±2 mm
12 years) Another aspect of the severity of wall thinning is its mapped extent on the economiser, as following: Wall thinning severity Very high High Modest Small
(y)
(z)
Suggested scale for frequency assessment (Quantitative and Qualitative)
Affected (to given thinning rate) area A A > 50% 10% < A < 50% 2% < A < 10 A 10 tube failures/year Very high 1 to 10 tube failures / year High 1 to 10 tube failures / 10 years Modest < 1 tube failure / 10 years Low 1) failures with clear contribution by wall thinning; for predicted failure rates Criteria
Quantitative > 10 / yr 1-10 / yr 0.1-1 / yr < 0.1/ yr can be also used
A probabilistic approach can be used to calculate PoF, combining the Methods and tools to calcu- effects of multiple mechanisms and input quantities, typically including wall thickness and its thinning rate, temperature, pressure (and late PoF when necessary, other loads), and materials strength. Appropriate tools (programs) available for the purpose are: • ALIAS – Risk • ALIAS – Creep • ALIAS – Fatigue
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Problem #1: Economiser tube failures due to wall thinning (aa) Controllability The following scale can be used for controllability / predictability of / predictability wall thickness: of the problem Criteria Controllability / pre- PoF indictability crease factor Good inspection records, no or Very good 1 few failures Fair inspection records, no or Good 2 few failures No/poor inspections, no or few Modest 4 failures No/poor inspections or many Poor 8 failures
(bb) Resources, constraints
The resources and constraints regarding wall thinning, together with the effect on PoF can be classed according to the following table: Criteria on resources / constraints Good inspectability/repairability Fair inspectability/repairability Limited inspectability/repairability Very limited inspectability/repairability
(cc) Economic consequences
Effect on PoF Low uncertainty
PoF increase factor 1
Medium uncertainty
2
Modest uncertainty
4
High uncertainty
8
Typically, wall thinning of economisers will inflict the following potential economic consequences: • inspection cost with accompanying preparation cost • repair / replacement cost • mitigation cost due to changes in operation or structures • loss of production (if any) The economic consequences can be rated as following: Condition Unplanned shutdown, wide replacement Unplanned shutdown, limited repairs No unplanned shutdown, wide replacement No unplanned shutdown, limited repairs
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Economic consequences High Considerable Modest Low
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Problem #1: Economiser tube failures due to wall thinning (dd) Environmental consequences
Wall thinning will usually not inflict major environmental consequences. Some impact could be expected from a high rate of failures, as these would increase operation under transient conditions and thereby with higher than average emission rates. The consequences can be rated as following: Condition > 10 unplanned shutdowns / year 1-10 unplanned shutdowns / year < 1 unplanned shutdown / year
(ee) Health and safety consequences
Environmental quences Modest Low Very low
conse-
Wall thinning of economisers will usually not inflict significant health and safety consequences.
6.8 Problem #2: Economiser Cracking
Problem #2: Economiser Cracking (a)
Problem Priority
-
(b)
Description
Cracking of economiser tubes can lead to early tube failures, causing water leakage and possibly subsequent secondary damage and failures by the escaping high pressure fluid.
(c)
Damage, cause of problem
Cracking of the economisers is often due to thermal or corrosion fatigue, or thermally induced repeated mechanical loading, which in case of corrosion fatigue is enhanced by the boiler environment. It is also possible that the underlying cause is poor water chemistry, leading to internal corrosion and corrosion fatigue cracking from the corrosion pits, or sometimes to hydrogen/methane damage from the hydrogen released in the corrosion process. Depending on the mechanism, cracking can initiate on either side of the tube wall.
(d)
Methods to find and quantify the symptoms
External cracking of economiser tubes is mainly observed and quantified by visual inspections, surface inspections (MT, PT), and other NDT inspections of the economiser. In case of cracking starting from the internal tube surfaces, the damage can be often observed by ultrasonic testing, and when necessary, diagnosed in more detail from a tube sample. Indications of early stage tube failures (leaks) may also be observable by acoustic emission monitoring.
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(e)
Extent of the problem
Economiser tube cracking can be described in terms of maximum dimensions of the cracks or cracked regions (crack length, maximum depth, in mm), depending on crack density and origin. Generally a crack is a local defect but in case of dense thermal fatigue cracking on surface, it may be possible to treat the case as in case of wall thinning (see above). The extent of the problem can be rated as following: Failure rate 1) Extent of cracking > 10 failures /year Very high 1 to 10 failures / year High 1 to 10 failures / 10 years Modest < 1 failure / 10 years Low 1) failures leading to shutdown
(f)
Scale for severity of the problem
Economiser tube cracking is generally related to both design and operation, when thermal fatigue type of mechanisms contribute to the problem, and more operations and water quality related when internal corrosion processes are involved. According to the mapped extent on the evaporator the severity can be considered as following: Severity Affected area A Very high A > 50% High 10% < A < 50% Modest 2% < A < 10 Small A 10 failures/year Very high > 10 / yr 1 to 10 failures / year High 1-10 / yr 1 to 10 failures / 10 years Modest 0.1-1 / yr < 1 failure / 10 years Low < 0.1/ yr 1) failures by thermal or corrosion fatigue; can be also used for predicted failure rates Criteria
A probabilistic approach can be used to calculate PoF, combining the Methods and tools to calcu- effects of multiple input quantities, typically including geometry, crack growth rate, temperature, loading, and material properties. late PoF Appropriate tools (programs) available for the purpose are: • ALIAS – Risk • ALIAS – Creep • ALIAS – Fatigue
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(i)
Controllability The following scale can be used for controllability / predictability of / predictability tube cracking: of the problem Criteria Controllability / PoF inpredictability crease factor Good inspection records, no or Very good 1 few failures Fair inspection records, no or few Good 2 failures No/poor inspections/monitoring, Modest 4 no or few failures No/poor inspections/monitoring , Poor 8 many failures
(j)
Resources, constraints
The resources and constraints regarding tube cracking, together with the effect on PoF can be classed according to the following table: Criteria on resources / Effect on PoF constraints Good inspectabilLow uncertainty ity/repairability Fair inspectabilMedium uncertainty ity/repairability Limited inspectabilModest uncertainty ity/repairability Very limited inspectabilHigh uncertainty ity/repairability
(k)
Economic consequences
PoF increase factor 1 2 4 8
Typically, economiser tube cracking will inflict the following potential economic consequences: • inspection cost with accompanying preparation cost • repair / replacement cost • mitigation cost due to changes in operation or structures • loss of production The economic consequences can be rated as following: Condition Economic consequences Unplanned shutdown, wide reHigh placement Unplanned shutdown, extensive reConsiderable pairs No unplanned shutdown, extensive Modest repairs No unplanned shutdown, no or few Low repairs 1) failures by cracking, can be also used for predicted failure rates
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(l)
Environmental consequences
Economiser tube cracking will usually not inflict major environmental consequences. Some impact could be expected from a high rate of failures, as these would increase operation under transient conditions and thereby with higher than average emission rates. The consequences can be rated as following: Condition > 10 unplanned shutdowns / year 1-10 unplanned shutdowns / year < 1 unplanned shutdown / year
(m)
Health and safety consequences
Environmental consequences Modest Low Very low
Economiser tube cracking will usually not inflict significant health and safety consequences.
7. Worked Examples 7.1 Multilevel risk analysis – power plant 7.1.1
Technical background
Note: German technical rules for boilers (TRD) and German standards used in this example are now European Standards (please see references). The following table shows the correlation between the documents. TRD / DIN Document TRD 300 DIN 17155 and DIN 17175 TRD 301 TRD 508
EU Standard – EN EN 12952-1 EN 12952-2 EN 12952-3 EN 12952-4
The PoF determination in this example is based on creep exhaustion (based on material uncertainties) and fatigue exhaustion. Creep exhaustion is determined using TRD creep curves (EN 12952-1, EN 12952-3), based on material data as shown in Figure 7-1. Fatigue exhaustion is based on low-bound TRD curve as shown in Figure 7-2. The creep curve is usually derived from the experimental data, according to recognized procedures, i.e. ECCC WG1 - Creep Data Validation and Assessment Procedures (ECCC WG1 1995). Fatigue curve is derived depending on the design temperature and using min[N/20, 2σa /2], where N is the number of cycles to crack initiation, and 2σa is stress amplitude. Inputs:
Component geometry according to TRD codes 300/301 (EN 12952-1, EN 129523), please see Figure 7-3. Design temperature and pressure (see Figure 7-4)
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Material data – average creep rupture strength for the component material and fatigue strength at given temperature Service time of the component – operational hours (see Figure 7-5)
Figure 7-1 Creep exhaustion calculation based on TRD (now EN 12952)
[MPa]
Fatigue Cycles at 400 °C
2
a
100000
10000
1000
100 10 TRD Curve
100
1000
2*Sigma
10000 20*N
100000 Mean
1000000 N mean
10000000
N
Figure 7-2 TRD Fatigue curve (with derived mean value curve) at 400°C
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Figure 7-3 Component geometry data
Figure 7-4 Design and operating temperature and pressure
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Figure 7-5 Service time of the component Based on data inputted and TRD rules exhaustions are calculated: ez – creep exhaustion ew – fatigue exhaustion It is assumed that average creep rupture strength and fatigue strength have a log-normal distribution, with 2σ1 (about 97.5% confidence level) at the lower (TRD) curve, and mean value µ on the mean curve as given by material data for creep.
f (t ) =
1 t 2πσ 12
e
⎛ ( ln (t )− µ1 ) ⎞ ⎜− ⎟ ⎜ ⎟ 2σ 12 ⎝ ⎠
where:
⎛
2 2 ⎞ ⎟, σ = ln⎛⎜ σ + µ ⎞⎟ ⎜ µ2 ⎟ ⎜ σ 2 + µ2 ⎟ 1 ⎝ ⎠ ⎝ ⎠
µ1 = ln⎜
µ2
σ and µ values are the values in the “real” (non-log scale), whereas σ1 and µ1 are values
(parameters) of the normal distribution in the log scale. Since we assume that the distribution is normal in the logarithmic space, we can calculate the parameter σ1 using the above equation as:
µ = MeanTimeToFailure σ1 = Which gives:
ln (MeanTimeTo Failure ) − ln (TRDTimeToF ailure ) 2
σ = µ ⋅ e (σ ) − 1 2 1
For example, using parameters defined as described above we calculate probability of failure based on creep, e.g. PoF(t≤ServiceTime=128000hours) = 4.31E-04% PoF(ServiceTime=128000hours ≤t≤ServiceTime=200000hours)= PoF(t≤ServiceTime=200000hours) - PoF(t≤ServiceTime=128000hours) = 5.84E-03% - 4.31E-04% = 5.41E-03% Revision number: 0
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Examples of distribution for creep and fatigue can be seen in Figure 7-6 and Figure 7-7, respectively.
[MPa]
Creep Rupture Strength at 520 °C 1000
0.6 0.5 0.4 0.3 0.2 0.1
100
0
1000
10000
100000
1000000
10000000 Tim e [h]
Average Creep Rupture Extrapol. 0.8 Time Mean
TRD Curve sigma Actual Time
Extrapol. A Time PoF
Figure 7-6 Example of distribution for creep rupture strength at 520°C
[MPa]
Fatigue Cycles at 400 °C
100000
0.35
2
a
0.3 0.25
10000
0.2 0.15
1000
0.1 0.05
100 10
TRD 100 Curve Mean N mean
1000
2*Sigma 10000 100000 sigma measured n
0 20*N 1000000 10000000 N N PoF
Figure 7-7 Example of distribution for fatigue strength at 400°C
7.1.2
Sample case
For the case of this example we will consider 8 components from a power plant. General information about the sample case plant: gas turbine 35 MWel and 60 MW of district heating with a coal-fired steam generator (195 MWel and 150 MW of district heating) commissioning 1982 gross output 230 MW
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net output 210 MW steam generating capacity 576 t/h district heating 210 MW fuel: low-grade coal methane gas converter gas operating hours: 126168 Components considered in this example: Name Mix-HEADER Water Separator SUPERHEATER 4 LI SUPERHEATER 4 RE HP-OUTLET SUPERHEATER SUPERHEATER-OUTLET Attemperator
Type Header Separator Superheater Superheater Header Header T-Piece Attemperator
From this 8 components 10 cases will considered (for 2 components additional failure mode will be considered)
7.1.3
Screening level
For the screening level of the analysis only the component design data is available. Additional the number of operating hours is also known. The following table shows the data available for the components.
Table 7-1 Component design data ComponentFailure mode
Type
Material
Service temperature
Service pressure
Operating hours
Mix-HEADER Leak Water Separator - Leak SUPERHEATER 4 LI - Leak SUPERHEATER 4 RE - Leak HP-OUTLET Leak SUPERHEATEROUTLET - Leak T-PIECE RA00 Leak Attemperator Leak SUPERHEATER 4 LI - break T-PIECE RA00 Break
Header
15NiCuMoNb5
280
238
126168
Separator
15NiCuMoNb5
390
225
126168
Superheater
X20CrMoV121
483
205
126168
Superheater
X20CrMoV121
483
205
126168
Header
X20CrMoV121
540
205
126168
Header
10CrMoV910
542
44.5
126168
T-Piece
X20CrMoV121
540
205
126168
Attemperator Header
X20CrMoV121
540
205
126168
X20CrMoV121
483
205
126168
T-Piece
X20CrMoV121
540
205
126168
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Based on available data and using TRD codes (now EN 14952), using e.g. ALIAS-TRD, service stress and exhaustion factors (ez – creep exhaustion, ew – fatigue exhaustion) were calculated (see Table 7-2)
Table 7-2 Calculated component exhaustion values Component-Failure mode
Type
Service stress
Ez [%]
Ew [%]
Etot[%]
Mix-HEADER - Leak Water Separator Leak SUPERHEATER 4 LI - Leak SUPERHEATER 4 RE - Leak HP-OUTLET - Leak SUPERHEATEROUTLET - Leak T-PIECE RA00 Leak Attemperator - Leak
Header Separator
135.796 110.189
0 5.52E-08
11.9 16.98
11.9 16.98
Superheater Superheater Header Header
108.709
1.6
26.49
28.09
88.408
0.3
19.73
20.03
65.209 26.996
20.9 8.6
22.67 8.188
43.57 16.788
T-Piece
63.146
18
24.98
42.98
Attemperator Header
92.32
53.9
24.98
78.88
108.709
1.6
26.49
28.09
T-Piece
63.146
18
24.98
42.98
SUPERHEATER 4 LI – break T-PIECE RA00 Break
Data was then inputted into RIMAP software (ALIAS-Risk, see ref. RIMAP 2002d), like shown in Figure 7-8. The following step is to define PoF and CoF classes. Following PoF classes were defined (see also Figure 7-9) PoF Ez – probability of failure based on creep exhaustion PoF Ew – probability of failure based on fatigue exhaustion PoF E – combined probability of failure for PoF Ez and PoF Ew
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Figure 7-8 Screening level PoF analysis in ALIAS-Risk
Figure 7-9 Defining PoF classes using ALIAS-Risk
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After defining PoF classes, consequence of failure classes were defined as following (see also Figure 7-10): Additional replacement cost (€) Typical repair cost (€) Production loss by failure (€) Overall replacement cost (€) CoF by leak – combined repair/production loss costs (€) Additional damage to other equipment cost (€) Combined replace/damage to other equipment cost (€) Replacement value (€) Current value (€) Overall damage by leak costs(€) CoF by break (€)
Figure 7-10 Defining CoF classes using ALIAS-Risk When the PoF and CoF classes were defined the failure scenarios (“Bow Tie” diagrams) for each component were made (see Figure 7-11). Example of a failure scenario for the superheater component can be seen in Figure 7-12.
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Figure 7-11 Building failure scenarios using ALIAS-Risk
Typical Repair Cost
Overall Damage by leak
PoF Ez
Additional Damage to other equipemen t
PoF: PoF E
SUPERHEATER 4 LI - Leak
CoF: CoF by Leak
Lost Production by Failure
PoFEw
Figure 7-12 “Bow Tie” for supeheater component In the next step PoF values were calculated based on inputted data and using ALIAS-TRD. Procedure was done like explained previously in this document (see 7.1.1 Technical background). Afterwards the calculated PoF values were imported into ALIAS-Risk (see Figure 7-13) and CoF values for each defined CoF class were inputted (see Figure 7-14). Revision number: 0
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Figure 7-13 Imported calculated PoF values
Figure 7-14 Input of CoF values Based on PoF and CoF values, following the previously defined scenarios (“Bow Tie” diagrams) for each component, risk is determined. Risk map (full report as well) are then automatically generated by ALIAS-Risk. The risk map for this example can be seen in Figure 7-15
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0.01 6
8 7 10
0.001
3
9
5
PoF
4 2
0.0001
1
Screening
0.00001 100
1000
10000
100000
1000000
10000000
Consequences (Euro)
Figure 7-15 Risk map after screening level 7.1.4
Intermediate level
After screening, next level of analysis is intermediate. Since monitoring data was available for this sample case it was decided to perform intermediate analysis for all 8 components/10 cases. Because of seamless transition between analysis levels in proposed RIMAP approach it is not necessary to perform all steps performed already in previous (screening) level. Based on monitoring data, new values of exhaustion based on creep and fatigue (according to TRD, now EN 14952) could be calculated. Since PoF and CoF classes, as well as the scenarios were already done in the previous step, the only necessary step in this level is to calculate again the PoF values based on updated values of exhaustion (the methodology is the same like in the screening level, only more data is available). The following table shows new calculated values of PoF: Component-Failure mode Mix-HEADER - Leak Water Separator - Leak SUPERHEATER 4 LI - Leak SUPERHEATER 4 RE - Leak HP-OUTLET - Leak SUPERHEATER-OUTLET - Leak T-PIECE RA00 - Leak Attemperator - Leak SUPERHEATER 4 LI – break T-PIECE RA00 - Break
Type
PoF
Header Separator Superheater Superheater Header Header T-Piece Attemperator Header T-Piece
2.03E-11 2.03706E-05 0.001345622 0.000587421 0.000448781 0.002393522 1.28E-04 8.35896E-05 0.001345622 1.28E-04
Newly calculate values were inputted into ALIAS-Risk and new risk map was generated automatically (see Figure 7-16). In order not to make the risk map overcrowded, only few components are shown in the figure.
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Interesting thing with Figure 7-16 is that it clearly shows the conservatism of low-level (screening) analysis when compared to intermediate. The arrows show how the components moved into the areas of lower risk from those determined in the screening level. 0.01
6
PoF
0.001
0.0001
10
8
2
Screening
Intermediate
Detailed
0.00001 100
1000
10000
100000
Consequences (Euro)
1000000
10000000
Figure 7-16 Risk map after intermediate analysis 7.1.5
Detailed level
For the most critical component (in our sample case, component 6 – SUPERHEATER Outlet, Header) it was decided to perform detailed analysis. The analysis was performed according to the schematics shown in Figure 7-19. All obtainable data for the component was gathered (including geometry, properties of the material used etc.) and the analysis was performed for several load cases (so called “worse cases”). The detailed analysis included: Stress calculation for the “worse cases” Creep analysis Fatigue analysis Critical crack size calculation Creep crack growth (see Figure 7-17) Fatigue crack growth Corresponding details about this analysis are given in the work of Jovanovic, Maile 2001 (see references).
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C* max
C* mittel
25
a [mm]
20
15
10
5
0
10000
100000
1000000
t [h]
Figure 7-17 Creep crack growth with C* (form factor 2.5) (Jovanovic, Maile, 2001)) After performing the detailed analysis and applying the statistical models (like shown in Figure 7-19), new value of PoF for the component was determined and plotted on the risk map (see Figure 7-18) Again it can be seen that the conservatism was preserved and that the detailed analysis moved the component on the risk map in the region of lower risk from those after screening and intermediate analysis. 0.01 6 6 0.001 6
0.0001
0.00001 100
1000
10000 Screening
100000
Intermediate
1000000
10000000
Detailed
Figure 7-18 Superheater component on a risk map after detailed analysis
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Brittle fracture, critical crack not detected at all.
POD
a Crack initiated due to creep only
D macrocracking a0 =0mm
p1 t AND σ
Crack initiated due to fatigue only
e.g. according to TRD code or EN 13445
PoF = p1 + p2 + p3
p2 OR
N
− p1 ⋅ p2 − p1 ⋅ p3 − p2 ⋅ p3
OR
+ p1 ⋅ p2 ⋅ p2
a0 assumed Crack initiated due to creep-fatigue
n i
Crack growth under cyclic loading (creepfatigue, thermal shock excluded) a0 =3mm Minimum detectable size of the crack
a0
a1
acr
p3
e.g. according to TRD code
e = ew + ez = =∑
p
n ti n +∑ i tRi N i i
a
p′3
p CCG FCG
acr Rm
Rσ
2 criteria diagram
a0
Rσ/Rk=2
t(N)
σ
Rσ/Rk=0.5
p3′′
t Rk
p
a0
acr
Crack propagation under assumed thermal shock(s).
p3′′′
Figure 7-19 Example of calculating PoF for the sample case considered
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7.2 Examples from process industry Note: the process industry examples are given as in work of Giribone, Pocachard, 2003 (see references)
7.2.1
Example of PoF calculation for distillation tower overhead system
7.2.1.1
Design information
In general, a distillation tower is composed of: • A top (⇒ overhead system): Light gas • A bottom: Heavy product • Several shells according to the separation degree The general material used are: • Carbon steel as the material of construction • Monel 400 / Stainless steel as lining / cladding to reduce corrosion problem in the upper part of the column Our study is held on the top part of the column, we will consider the following : • Material of construction = Carbon steel • Internal lining = Monel 400 • Trays = SS 304
As design data: • Design thickness = 16 mm • Design pressure = 3.5 bar 7.2.1.2
Process information
We will consider that the column top is in presence of the following fluid:
Table 7-3 Distillation tower Top part - Process
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H2S
some ppm
H2O
1% wt.
Chlorides
5 ppm
C1-C2
4% wt.
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C3-C4
30% wt.
C5
8% wt.
C6-C8
56% wt.
Mercaptans
some ppm
The operating conditions are : • Temperature = 130°C • Pressure = 2.5 bar We will consider 2 cases: • No inhibition is performed on the overhead system. • Inhibition is performed (use of neutralising amine / caustic soda injected in the overhead system of the column) in order to reduce / control the pH. We can then consider the following typical values for the corresponding pH: • pH (without inhibition) = 4 • pH (with inhibition) = 6 7.2.1.3
Corrosion information
According to description of distillation tower overhead system, (see 7.2.1.2), the possible corrosion problems that the equipment can face are: • Hydrochloric acid (HCl) corrosion. • CO2 corrosion (Not applicable in our case). • Low acid corrosion (Not applicable in our case). • H2S corrosion (Cracking problem) • Sulfuric and sulphurous acids (Not applicable in our case). We will focus our analysis only on the HCl corrosion (which is a thinning mechanism). To sum up the data: • Temperature = 130°C • Pressure = 2.5 bar • pH (without inhibition) = 4 • pH (with inhibition) = 6 • Material of construction = Carbon steel • Internal lining = Monel 400 • Trays = SS 304 • [Cl-] = 5 ppm According to the previous data, we can estimate a corrosion rate28: • Without inhibition For carbon steel : Corrosion rate = 3 mm/year For Monel 400 : Corrosion rate = 0.7 mm/year For SS 304 : Corrosion rate = 0.9 mm/year • With inhibition For carbon steel : Corrosion rate = 0.7 mm/year For Monel 400 : Corrosion rate = 0.05 mm/year For SS 304 : Corrosion rate = 0.1 mm/year The use of a filming amine can help reducing these corrosion rates.
28
This corrosion rate correspond to the general one. To consider the pitting, the corrosion rate can be multiplied by 10.
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7.2.1.4
Pof Calculation
No inhibition For the following calculations we will consider the corrosion rate to be equal to 0.7 mm/year. The equipment has already spent 5 years in the previous service. Structural reliability Let us consider the following set of data : • Material: Alloy 400 (Monel) with and without corrosion inhibition • UTS= 485 MPa • Limit state function: M= g(R,D) = R-D • Probability distribution: Normal The coefficients of variation are taken equal to the following values: • cS = 12% • cD = 15% The design stress is taken as: f = 162 MPa which corresponds to a traditional safety factor SF = 3 The initial thickness is 16 mm and corrosion rate r = 0.7 mm/year. Reliability assessment is performed at time ∆t = 5 years.
Table 7-4 Probability of failure after 5 years Damage Strengt states h (MPa) Initial 485 1 (r = 485 0.7) 2 (r = 485 1.4) 3 (r= 2.8) 485
Thickness (mm) 16
Stress (MPa) 161.67
γ
β
Pf
3.00
5.13
1.47×10-7
12.5
206.94
2.34
4.22
1.25×10-5
9
287.41
1.69
2.73
3.19×10-3
2
1293.36
0.37
-3.99
1
Bayesian update We will consider the following: It is assumed that the history of the studied top provide low reliability data. We will compare the effect of the following inspection effectiveness: • Highly effective (H.E.) •
Usually effective (U.E.)
•
Fairly effective (F.E.)
The following calculations are based on the document “Principles of failure probability assessment”. Then, before inspection:
Table 7-5 Assumed value of PoF before any inspection
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Damage states
Probabilities
1 2 3
0.5 0.3 0.2
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After inspection:
Table 7-6 Value of probability after the 1st inspection Damage states
After H.E.
After U.E.
After F.E.
1 2 3
0.939 0.056 0.004
0.814 0.140 0.047
0.658 0.237 0.105
Global results Considering the structural reliability results and the effect of the Bayesian update, we obtain:
Table 7-7 PoF results after completion of a highly effective inspection Damage states 1 (r = 0.7) 2 (r = 1.4) 3 (r= 2.8) TOTAL
Pf 1.25×10-5 3.19×10-3 1
LoD29 (before inspection) 0.5 0.3 0.2
Pf (No inspection) 6.25×10-6 9.57×10-4 0.2 0.20096
LoD (after inspection) 0.939 0.056 0.004
Pf (after inspection) 1.17×10-5 1.79×10-4 0.004 4.19×10-3
Table 7-8 PoF results after completion of a usually effective inspection Damage states 1 (r = 0.7) 2 (r = 1.4) 3 (r= 2.8) TOTAL
Pf 1.25×10-5 3.19×10-3 1
LoD (before inspection) 0.5 0.3 0.2
Pf (No inspection) 6.25×10-6 9.57×10-4 0.2 0.20096
LoD (after inspection) 0.814 0.140 0.047
Pf (after inspection) 1.02×10-5 4.47×10-4 0.047 4.75×10-2
Table 7-9 PoF results after completion of a fairly effective inspection Damage states 1 (r = 0.7) 2 (r = 1.4) 3 (r= 2.8) TOTAL
Pf 1.25×10-5 3.19×10-3 1
LoD (before inspection) 0.5 0.3 0.2
Pf (No inspection) 6.25×10-6 9.57×10-4 0.2 0.20096
LoD (after inspection) 0.658 0.237 0.105
Pf (after inspection) 8.22×10-6 7.56×10-4 0.105 0.1058
Even if the corrosion rate is important, the inspection process is “able” to reduce significantly the probability of failure.
29
LoD stands for “Likelihood of Damage” = Likelihood to have detected the damage that was a priori estimated.
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We notice that in the case of a highly effective inspection, this reduction can lead to an acceptable PoF value. On the other hand, a fairly effective inspection divides by 2 this probability of failure, however, the result remains insufficient to make the PoF acceptable : a 2nd inspection will probably help in reducing this PoF. With inhibition For the following calculations we will consider the corrosion rate to be equal to 0.05 mm/year. The equipment has already spent 5 years in the previous service. Structural reliability Let us consider the following set of data : • Material: Alloy 400 (Monel) with and without corrosion inhibition • UTS= 485 MPa • Limit state function: M= g(R,D) = R-D • Probability distribution: Normal The coefficients of variation are taken equal to the following values: • cS = 12% • cD = 15% The design stress is taken as: f = 162 MPa which corresponds to a traditional safety factor SF = 3 The initial thickness is 16 mm and corrosion rate r = 0.05 mm/year Reliability assessment is performed at time ∆t = 5 years.
Table 7-10 Probability of failure after 5 years Damage states Initial 1 (r = 0.05) 2 (r = 0.1) 3 (r= 0.2)
Strength (MPa) 485 485 485 485
Thickness (mm) 16 15.75 15.5 15
Stress (MPa) 161.67 164.24 166.88 172.45
γ
β
Pf
3.00 2.95 2.91 2.81
5.13 5.07 5.02 4.91
1.47×10-7 1.94×10-7 2.57×10-7 4.62×10-7
Bayesian update We will consider the following: It is assumed that the history of the studied top provide low reliability data. We will compare the effect of the following inspection effectiveness: • Highly effective (H.E.) • Usually effective (U.E.) • Fairly effective (F.E.) The following calculations are based on the document “Principles of failure probability assessment”. Then, before inspection:
Table 7-11 Assumed value of PoF before any inspection
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Probabilities
1 2 3
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After inspection:
Table 7-12 Value of probability after the 1st inspection Damage states
After H.E.
After U.E.
After F.E.
1 2 3
0.939 0.056 0.004
0.814 0.140 0.047
0.658 0.237 0.105
Global results Considering the structural reliability results and the effect of the Bayesian update, we obtain:
Table 7-13 PoF results after completion of a highly effective inspection Damage states 1 (r = 0.05) 2 (r = 0.1) 3 (r= 0.2) TOTAL
Pf 1.94×10-7 2.57×10-7 4.62×10-7
LoD30 (before inspection) 0.5 0.3 0.2
Pf (No inspection) 0.97×10-7 0.77×10-7 0.92×10-7 2.66×10-7
LoD (after inspection) 0.939 0.056 0.004
Pf (after inspection) 1.82×10-7 1.44×10-8 1.85×10-9 1.98×10-7
Table 7-14 PoF results after completion of a usually effective inspection Damage states 1 (r = 0.05) 2 (r = 0.1) 3 (r= 0.2) TOTAL
Pf 1.94×10-7 2.57×10-7 4.62×10-7
LoD (before inspection) 0.5 0.3 0.2
Pf (No inspection) 0.97×10-7 0.77×10-7 0.92×10-7 2.66×10-7
LoD (after inspection) 0.814 0.140 0.047
Pf (after inspection) 1.58×10-7 3.60×10-8 2.17×10-8 2.16×10-7
Table 7-15 PoF results after completion of a fairly effective inspection Damage states 1 (r = 0.05) 2 (r = 0.1) 3 (r= 0.2) TOTAL
Pf 1.94×10-7 2.57×10-7 4.62×10-7
LoD (before inspection) 0.5 0.3 0.2
Pf (No inspection) 0.97×10-7 0.77×10-7 0.92×10-7 2.66×10-7
LoD (after inspection) 0.658 0.237 0.105
Pf (after inspection) 1.28×10-7 6.09×10-8 4.85×10-8 2.37×10-7
As the corrosion rate is very low, even if the probability to detect a wrong result exists, the risk of error is controlled. An effective inspection will help to confirm the slow corrosion process. 30
LoD stands for “Likelihood of Damage” = Likelihood to have detected the damage that was a priori estimated.
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7.2.2
Example of PoF calculation for HF stripper top
7.2.2.1
Calculation process
As SCC is a non trendable damage, the simple analysis performed for thinning is not applicable. Then, the calculations have to be adapted in order to consider or not this intrinsic characteristic. It is proposed to follow :
NO
Cracks have been detected during inspection
YES
Cracks dimension (a)
PoD X % - Result OK Y % - Result not OK
API 581 calculations process
Result OK
Result not OK
Structural Reliability calculations with (a)
Structural Reliability calculations with (1,5.a)
PF1
PF2
Probability of Failure directly connected to the PoD/Damage
Pf = PF1 + PF2
Figure 7-20 Calculation process – non trendable damages Note:In the case “Cracks have been detected” and “Result not OK”, the structural reliability calculations are performed using a default size of 1.5a. This value is only an hypothesis : it can be refined. 7.2.2.2
Design information
The general material used are: • Carbon steel • Monel 400 Our study is held on the top part of the stripper, we will consider the following : • Material of construction = Carbon steel As design data: • Design thickness = 10.4 mm • Design pressure = 3.5 bar 7.2.2.3
Process information
We will consider that the column top is in presence of the following fluid:
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Table 7-16 Distillation tower Top part - Process HF
10 % wt.
H2O
1% wt.
C3-C4
89% wt.
The operating conditions are : • Temperature = 56°C • Pressure = 12.5 bar 7.2.2.4
Corrosion information
As we are looking at the HSC damage mechanism, it is not possible to characterize this damage by a corrosion rate but by a susceptibility to the damage. This susceptibility translate the ability for the equipment to cope with the corrosive environment. The lower it is, the lower is the effect of the corrosive middle on the material. In our case, the principal factor impacting this susceptibility are: • Post welding heat treatment (PWHT) • Material Brinell hardness • Material sulfur content • Is equipment rolled and welded during forming ? • HF content The data are:
Table 7-17 Hydrogen embrittlement corrosion data PWHT Material Brinell hardness Material sulfur content Rolled and welded plate ? HF content
Yes < 200 HB > 0.01% No 10% wt.
We obtain in these conditions: • Hydrogen-Induced Cracking : High susceptibility • Hydrogen Stress Cracking : No susceptibility To conclude : The top of the stripper is very likely to suffer from Hydrogen-Induced Cracking caused by the dissolution of HF due to aqueous electrochemical reaction of this HF with the iron of the material. 7.2.2.5
Inspection history
Let’s consider the equipment have been inspected in the past. We will assume that the equivalent number of inspection is 2 corresponding to a highly effective inspection. The last inspection was performed 2 years ago. 7.2.2.6
PoF calculation
For the following calculations we will consider that the equipment has already spent 10 years in the previous service without any degradation. We will consider in our analysis the following 2 cases: • The inspection has not detected any cracks in the material nor close to the weldings.
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•
The inspection has detected some cracks. We will consider for the calculation the one with the highest length a. Inspection result = No cracks have been detected Methodology As proposed, we will use the API 581 methodology. For that, we will use the following scheme: Equipment susceptibility to the damage
Severity index
Inspection data (number & effectiveness) Last known state
STRUCTURAL RELIABILITY + BAYES UPDATE
Time since last inspection Generic frequency of failure
DAMAGE FACTOR
Probability of failure Pf
Figure 7-21 API 581 calculation process for non trendable damages 8. RISK Consideration In order to avoid repeating, the issues regarding risk reduction, risk mitigation and links to life management plan and risk aggregation are not discussed here as they are already given in other RIMAP documents. Please refer to RIMAP D3.1 document, “Risk Assessment Methods for use in RBIM” and especially to:
Chapter 7: Mitigating activities and risk reduction Appendix D: Inspection and probability of detection Appendix E: Evaluation and risk aggregation Appendix G: Acceptance criteria
9. Conclusions RIMAP Application Workbook for Power Industry represents a full, “hands on”, RIMAP application guide for performing a risk analysis mainly concentrating on the equipment and problems that can be found in power plants. Furthermore it gives references to documents and examples for other types of industries where similar components are used. Furthermore this workbook has an extension in form of two additional workbook parts (PART II and PART III)
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which give more detailed information on components, including tables with values for failure rates, consequences etc. as well as detailed description of problems that can occur on types of components used in power industry.
10. References [API] (1998). API Publication 581, Base Resource Documentation - Risk-Based Inspection, First Edition, Order # No.: C58101, © 1995-1999, American Petroleum Institute [API] (1999). API Publication RP 580, Recommended practice for risk-based inspection, © 1999, American Petroleum Institute [API] (2000a). API Publication 581, Base Resource Documentation - Risk-Based Inspection, May 2000, © 2000, American Petroleum Institute [API] (2000b). API Publication 580, Risk-Based Inspection, API Recommended Practice, Draft #2, May 2000, © 2000, American Petroleum Institute [API] (2000c). API Publication 580, Risk-Based Inspection - Lite Version, API Recommended Practice, Draft #1, May 2000, © 2000, American Petroleum Institute [EPRI] (1998). EPRI – Productivity Improvement Handbook for Fossil Steam Power Plants, TR-111217 (1998), A.F. Armor, R.H. Wolk, EPRI [IEEE] (1986), Standard Reliability Data for Pumps, and Drivers, and Valve Actuators: The Institute of Electrical and Electronics Engineering, Inc. ISBN-0-471-85686-X; New York, 1986 [KKS] (1988). KKS – Kraftwerk-Kennzeichensystem, VBG-KRAFTWERKSTECHNIK GmbH, December 1988 [NERC] (1999) North American Electric Reliability Council – GADS service; Generating Availability Reports (see http://www.nerc.com/~gads/) [OREDA] (1997). OREDA Offshore Reliability Data, 3ra Edition April 1977, SINTF Industrial Management, Safety and Reliability, N-7034 Trondheim, Norway, (1997) [RAC] (1999). Reliability Analysis Center, Database Version 2.20, IIT Research Institute, New York, 1999 (see http://rac.iitri.org/iPC/servlet/iPCServlet?NPRD-95C) [RIMAP] (2004) D3.1 Risk Assessment Methods for use in RBIM (with appendices). Ref.Nr. 3-31-F-2004-01-1, RIMAP Consortium 2004. [VDI] (1984). VDI 3822 Schadensanalyse (Failure Analysis), VDI Richtlinie, VDI-Gesellschaft Werkstofftechnik, Verein Deutscher Ingenieure – VDI, Februar 1984 Giribone, R. Pocachard, M. (2003). Process Workbook – Examples. BV Report: E&P 10428, 2003. Jovanovic (2001). Risk-based Life Management of Critical Components in Power and Process Plants Supported by Knowledge Management Systems, Dr. Hab. Dissertation, Stuttgart, 2001
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Jovanovic, A. Maile, K. (2001). MPA Report – Ergebnisdokument, Auft.Nu.: 949749003. MPA Stuttgart, October 2001. Koppen, G. (1998). Development of risk-based inspection, Proc. of the First Intl. Conf. on NDE Relationship to Structural Integrity for Nuclear and Pressurised Components, vol. II, 2022 Oct. 1998, Amsterda, Bieth and Mojaret, Eds., Woodhead Publishing Ltd. Pasha, A. Allen, R. (2003). Operation and maintenance: Question of integrity. Power Engineering International, journal. Issue January/February, 2003. pp. 28-29. Saaty T. L. (1990). How to make a decision: The Analytic Hierarchy Process, European Journal of Operational Research 48, 1990, pp. 9-26 Steuer R. E. (1986). Multiple Criteria Optimization: Theory, Computation, and Application, New York, Wiley 1986
`
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Contact information Det Norske Veritas AS (DNV) Mr. Sture Angelsen Veritasveien 1 N-1322 Høvik Norway Tel: +47 67 57 99 00 E-mail: Sture.Anglesen@ dnv.com URL: www.dnv.com
Bureau Veritas (BV) Mr. Rémy Giribone Place des Reflets 17 BIS Place La Defense 92400 Courbevoie, CDEX 44 France Tel: +33 1 42 91 54 27 E-mail: remy.giribone@ bureauveritas.com URL: www.bureauveritas.com
Staatliche Materialprüfungsanstalt (MPA Stuttgart) Dr. Aleksandar Jovanovic Pfaffenwaldring 32 D-70569 Stuttgart Germany Tel: +49 711 685 3007 E-mail: jovanovic@ mpa.uni-stuttgart.de URL: www.mpa.uni-stuttgart.de
Technical Research Centre of Findland (VTT) Mr. Pertti Auerkari Kemistintie 3 Postbox 1704 FIN-02044 VTT, Espoo Finland Tel: +358 9 456 6850 E-mail: Pertti.Auerkari@ vtt.fi URL: www.vtt.fi
TÜV Industrie Service TÜV SÜD Group Dr.Ing. Robert Kauer Westendstrasse 199 D-80686 München Germany Tel: +49 (89) 57 91 12 77 E-mail: robert.kauer@ tuev-sued.de URL: www.tuev-sued.de
TNO Industrial Technology Metals Technology (TNO) Mr. Jan Heerings Rondom 1 P.O.Box 6235 5600 HE Eindhoven Netherlands Tel: (+31) 40 265 0275 E-mail: [email protected] URL: www.tno.nl
Hydro Agri Sluiskil B.V. (HAS) Mr. Arie deBruyne Industrieweg, Postbox 10 4541 HJ Sluiskil Netherlands Tel: +31 (0) 115 47 41 16 E-mail: arie.de.bruyne@ hydro.com URL: www.hydro.com
Mitsui Babcock Energy Limited (MBEL) Dr. Barrie Shepherd Technology and Engineering Porterfield Road Renfrew, Renfrewshire PA4 8DJ UK Tel: +44 (0) 141 885 3977 E-mail: bshepherd@ mitsuibabcock.com URL: www.mitsuibabcock.com
ExxonMobil Chemical Ltd. (EXXONMOBIL) Mr. Andrew Herring Beverkae House, Mossmorran KY4 BEP Cowdenbeath Fife Scotland Tel: +44 (0) 1383 846142 E-mail: andrew.herring@ exxonmobil.com URL: www.exxonmobil.com
Energie Baden-Württemberg Ingenieure GmbH AG (EnBW) Dipl.-Ing Jörg Bareiβ Postbox 10 13 11 D-70012 Stuttgart Germany Tel: +49 (0711) 128 21 24 E-mail: j.m.bareiss@ enbw.com URL: www.enbw.com
Siemens Aktiengesellschaft (SIEM) Dr. Artur Ulbrich Wiesenstraβe 25 D-45466 Mülheim a.d. Ruhr Germany Tel: +49(208) 456 2853 E-mail: artur.ulbrich@ kwu.siemens.de URL: www.siemens.de
European Commission, Directorate General Joint Research Centre, Petten (JRC) Dr. Luca Gandossi Postbox 2 1755 ZG, Petton Netherlands Tel: +31 224 565250 E-mail: [email protected] URL: www.jrc.nl
Electricity Supply Board (ESB) Dr. Alan Bissell 27 Lower Fitzwilliam Street Dublin 2 Ireland Tel: +353 (1) 702 6467 E-mail: [email protected] URL: www.esb.ie
CORUS UK Ltd. (CORUS) Mr. Colin Davies Moorgate Rotherham South Yorkshire S60 3AR UK Tel: +44 (0) 1709 823105 E-mail: colin.davies@ corusgroup.com URL: www.corusgroup.com
Dow Benelux N.V. (DOW) Mr. Antoine Baecke H. Dowweg Postbox 48 430AA Terneuzen Netherlands Tel: +31 115 67 2667 E-mail: [email protected] URL: www.dow.com
SOLVAY S.A. (SOLVAY) Mr. Alain Fobelets Rue de Ransbeek Postbox 310 B-1120 Bruxelles Belgium Tel: +32 2 264 3655 E-mail: Alain.Fobelets@ solvay.com URL: www.solvay.com
DNV Library Services, Veritasveien 1, N-1322 Høvik, Norway Contacts Judit Berthelsen tel (+47) 67 57 81 29
Mette Nore Ingunn Lindvik Sigrun Rosholt
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