OSIO Model Questions Pre Treatment Final [PDF]

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3. Model Question Paper for PRE-TREATMENT 1. How Steel surface shall be treated from the following prior to surface treatment or surface preparation? a) Welds – Smoothed by using grinder

b) Sharp Edges – Rounded to specified radius (e.g.: 2mm or 4mm) by grinder

c) Cutting Edges – Remove rough edges using grinder to smooth and radius the edge

d) Laminations – Remove by using grinder

e) Contaminations (oil, Grease, cutting compounds etc.,) – Remove by degreasing the surface

f) Salts (Chlorides, Sulphates & Nitrites etc.,) – Remove by degreasing the surface

g) Weld Smoke – Remove by water washing (Solvents will not remove welding smoke sufficiently) 2. What are Initial Conditions? What is the other name of Initial Conditions? Initial condition is the condition of the metal surface whether it is new or previously coated metal. As per ISO 8501-1, the four grades of steel surface conditions are A – Full of Mill Scale B – Mill Scale with rust C – Full of Rust D – Rust with Pitting’s  Initial conditions are also called as rust grade / steel surface condition / metal condition. 3. How is Inspector assessing (Inspecting) the rust grades?

Inspector assess the rust grades using visual reference photograph from ISO 8501-1 4. How many rust grades are available in Carbon Steel? According to ISO 8501-1, there are four rust grades: A – Full of Mill Scale B – Mill Scale with rust C – Full of Rust D – Rust with Pitting’s 5. Which ISO standard describing the Rust grades? ISO 8501 - 1

6. Which SSPC Standard describing the rust grades? SSPC VIS SSPC VIS 1 – Abrasive Blast cleaning SSPC VIS 2 – Evaluation of degree of rust on painted steel SSPC VIS 3 – Hand & Power tool cleaning SSPC VIS 4 – Water jetting SSPC VIS 5 – Wet abrasive blast cleaning 7. What is the standard procedure to remove water soluble salts? Water jetting

8. Which ISO Standards describing the methods to Extract and analyze the water-soluble salts? ISO 8502 – part 6 & 9 9. When conducting Water soluble salts by ISO 8502- part 6, how many methods Inspector can extract the salts from the steel?  Bresle patch Method

10. Which method and standard the Inspector analyzing the water-soluble salts? ISO 8502 – 9 – Field Method for Conductometric determination water soluble salts. // 11. What two variables (assessments) we are getting while assessing the salts?  Specific Ion (Salt-specific) Chloride Sulphate Ferrous Nitrate  Conductivity (Non-Salt – specific) 12. How are Contractors removing Chemical contaminations? What methods they will deploy to remove surface contaminations? Contractors normally remove chemical contaminations by pressure washing or water jetting using clean water. Methods to remove surface contaminations:  Fresh water cleaning (preferably pressurized water)

  

Solvent Cleaning Steam cleaning Non solvent degreasers (water with detergent, alkaline cleaners, emulsion cleaners)

13. What are the maximum salt levels accepted as per standards? There are no standards specifying the acceptance level of soluble salt. 14. As an Inspector, how you will verify there is no presence of any contamination? Define the Test methods and acceptance criteria? Solvent Cleaning – No oil or grease (Visual, water break test, black light test, chalk powder) Compressed air cleanliness – No oil or water Blotter test

15. What is the international standard for Degreasing? SSPC SP 1 16. Define Solvent cleaning? It is the process of removing visible oil, grease, dust, lubricants, cutting compounds, from the surface. 17. After solvent cleaning, what would be the next step? Surface preparation / Surface treatment 18. What is Pre-treatment? Explain the process under pre-treatment? It is the process of removing manufacturing defects, fabrication defects and surface contaminations from the metal substrate. Process: 1. Steel dressing: All manufacturing and fabrication defects are removed, where shape of the metal is under scrutiny 2. Solvent cleaning: All visible oil, grease, lubricants & other contaminations are removed from the surface.

19. What are all Fabrication defects? How will you treat it?



Weld ripple/profile: Sharp profile peaks to be smoothed using grinder



Weld spatter: Remove by hammer, grinder according to specified grade



Flame cut: Remove rough edges using grinder to smooth and radius the edge



Sharp edge: Round to specified radius (e.g. 2mm) by grinder



Rolled-in extraneous matter: Remove using grinder



Undercut: Weld undercuts require re-welding and grinding



Weld porosity: Treat by either welding/grinding or enlarge the pore for paint penetration



Pits and craters: Either welding/grinding or enlarge for paint penetration

20. What are all steel manufacturer’s defects or flaws? How will you treat these defects? Lamination, shelling, slivers, hackles – Remove using grinder 21. Which ISO standard describing the pre-treatment to steel (Welds, Corners, edges etc.,)? ISO 8501 – 3 22. While carrying our pre-treatment which types of tools being employed? Hand and power tools 23. Describe the various hand & power tools deployed for pre-treatment? 

Grinder



Hammer



Chisel

24. What are the advantages and disadvantages of cup wire brush?

Advantages  It is used for preparing the surface, deburring and surface finishing  It is commonly used on large areas to remove mill scale, rust & paint.  It provides a wide area of surface contact Disadvantages  Wire brushes are normally made up of hardened carbon steel so it can damage soft metals such as copper, brass & aluminum alloys.  It will swirl marks on the metal surfaces 25. What are the advantages and disadvantages of Sanding disc?

Advantages  To smooth the materials  It is ideal for end grain work, shaping subtle round corners and removing large amounts of material quickly Disadvantages  Sanding on the upward side could cause the work piece to fly up causing injury  Aggressive power can damage a work piece.



Sanding on contaminated areas will spread the contamination to the adjacent areas, which causes coating defects during paint application.

26. What are the advantage and disadvantages of wire brush?

Advantages  Remove paint, coating or any form of corrosion products.  To prepare for welding  Roughen and deburr the surface  Polish by removing deposits Disadvantages:  Different wire brushes are used depending on the substrate for example brushing stainless or aluminum requires stainless steel or aluminum wire brush to prevent corrosion  Wire brushing during hazardous scenarios may cause spark formation. 27. What is Surface treatment & Surface preparation? Is both words are same or different? Yes, surface treatment & surface preparation are both same 28. How many types of surface treatment available in Industries?  Abrasive blast cleaning



Vacuum blast cleaning



Centrifugal blast cleaning



Hand and power tool cleaning



Water jetting



Wet abrasive blast cleaning



Chemical stripping



Pickling

29. What are the best ISO standards for deciding the type of surface preparation (methods) being used? ISO 8504 30. What is the requirement for accepting surface preparation after blast cleaning?

Visual verification using ISO 8501 – 1 31. Which standard describing Surface preparation requirements? ISO 8504 32. Apart from ISO 8501-1, is there any international standards involving in surface preparation cleanliness standards? SSPC 33. According to ISO 8501-1 (Pictorial representation) how many color photos are displayed in that book? Please write a detailed explanation? Rust Grade A B, C, D

Abrasive Blast Cleaning Sa 3, Sa 2 1/2 Sa3, Sa2 ½, Sa2, Sa1

Hand and power tool cleaning St 2, St3

Flame Cleaning F1 F1

Rust grade – 4 Abrasive blast cleaning -14 Hand and power tool cleaning – 6 Flame cleaning – 4 Total photos – 28 34. According to SSPC Surface cleanliness standards, how many standards are available for abrasive blasting to carbon steel? Five Standards 35. What is surface cleanliness standard for Brush-off blast cleaning to Carbon steel? SSPC SP – 7 36. What is surface cleanliness standard for Brush-off blast cleaning to non-ferrous items? SSPC SP – 16 37. What is the former standard name for ISO 8501-1? Rust grades and preparation grades of uncoated steel substrates and of steel substrates after removal of previous coatings 38. According to ISO 8501-1, the cleanliness standard mentioned as ISO Sa 3, So, what is Sa means? Swedish Abrasive or Standard Abrasive

39. According to ISO 8501-1, the Hand & Power tool cleaning standard as ISO St3, so, what is St means? Swedish tooling or Standard tooling

40. Which ISO standard, describing the surface profile measurement requirements using Comparator? ISO 8503 - Part 2 (ISO Surface Profile Comparator)

41. Which ISO standard, describing the surface profile measurement requirements using Testex Tape (Replica Tape) method? ISO 8503- Part 5 (Replica Tape method)

42. When you are using Comparator to measure surface profile, what is the maximum magnification limit allowed? What is the general magnification we are using? 5X normally we are using and 7X is the largest limit for magnifying. 43. How to calibrate Surface Profile Comparator? The comparator is calibrated by measuring each of the profiles on the reference surface by either using focusing microscopic method (ISO 8503-3) or stylus instrument method (ISO 8503-4).

44. Is that hand lens (Magnifier) usage is being mandatory while carryout surface profile measurement by using Comparator?

Yes, Magnifier is compulsory needed to assess & grade the test surface with the segments of the comparator. 45. What is “Primary” Surface Profile & “Secondary” Surface Profile? primary profile original surface profile prior to blast-cleaning. secondary profile surface profile resulting from the effect of the blast-cleaning process on the primary profile

46. What is the definition of Hackles? Thin raised slivers of steel, still attached to the substrate, which are caused by the impact of abrasives on a steel surface during blast-cleaning and which sometimes protrude above the other peaks 47. What is Slivers in Carbon Steel? Slivers are segments of steel that have been torn from the steel and rolled onto the surface of the metal. This defect is most common in low strength steel which can easily tear due to incorrect or high-speed rolling processes. Slivers can also start from defects that were not previously removed by conditioning.

48. What is lamination in Carbon Steel? A lamination is a type of thin and flat discontinuity found in a base material that is a separation of one portion of the material from another. A lamination is usually created during a forming process. Because a lamination is a separation of a base material, it can negatively affect its mechanical properties, rendering it more susceptible to material failure and corrosion.

49. In which ISO standard, the Surface preparation methods are detailed? ISO 8504- Part 2 (Abrasive Blasting Methods) ISO 8504- Part 3 (Hand & Power tool cleaning methods) 50. Which ISO Standards describing the assessment of Rust Grades, Mill Scale, Contaminations (Oil, Grease & Salts) and Surface Profile? Which standard will give to surface Preparation methods? ISO 8501 — Visual assessment of surface cleanliness; ISO 8502 — Tests for the assessment of surface cleanliness; ISO 8503 — Surface roughness assessment of blast-cleaned steel substrates; ISO 8504 — Surface preparation methods.

51. What is the Most effective Surface Preparation method in Coating Industries? Abrasive Blast Cleaning Method 52. What are the advantages & Disadvantages of Abrasive Blast Cleaning method? ADVANTAGES a) High Production rate b) Blast pots can be moved to any locations. c) Any shapes and sizes can be blasted d) Various Grades of surface cleanliness and various grades of surface profile can be achieved.

e) Any abrasives can be used f) Economical method Disadvantages a) b) c) d) e) f) g)

High dust producing Skilled operators required Dangerous activity due to high pressure involved Poor visibility Wear & Tear of Equipment and accessories High Noise pollution Compulsory PPE required (including Respiratory mask)

53. What is the simple definition of “Abrasive Blast-Cleaning?

During Blast cleaning, the abrasive will hit the substrate and remove all contaminations (i.e., Rust, Mill scale, Old paints and other contaminations). “Impingement of a high-kinetic-energy stream of abrasive on to the surface to be prepared” 54. What is the definition of “Abrasive Blasting Materials”? Abrasives (Garnet, Steel Shot, Steel Grit, Copper slag, Coal Slag, Aluminium Oxide, Nickel Slag, Plastic pellets, Glass beads, Dry Ice, Sodium bicarbonate, Caustic soda, Coconut shell, walnut shell, cryogenic materials, Laser) used for abrasive blastcleaning 55. What is the definition of SHOT abrasive?  Shot abrasives are ROUND or SPHERICAL in shape.  Shot abrasives are obtained from Ferrous (Steel shot) or Non-Ferrous (Plastic balls or glass balls)  Used for Blasting purposes  Used for shot peening purposes  Shot creates peening effect particles that are predominantly round, that have a length of less than twice the maximum particle width and that do not have edges, broken faces or other sharp surface defects 56. What is the definition of GRIT abrasive?  Grit having ANGULAR Shape  Grit produce Gouging or Shaving effect  Grit used for blasting purposes  Grit may be reused for economical purpose  Once hit the substrate, creates a new cutting edge  Grit can either Ferrous or Non-Ferrous particles that are predominantly angular, that have fractured faces and sharp edges and that are less than half- round in shape 57. What is Cut wire Abrasives? sharp-edged particles, having a diameter-to-length ratio of 1:1, cut so that their faces are approximately at right angles to their centreline 58. What are the factors to be considered while selecting right abrasive materials? a) Type b) Particle size (mesh size) c) Chemical properties d) Hardness 59. How many types of abrasives available? Which ISO standards dealing with those abrasives? Metallic Abrasive Types

– ISO 11124

Metallic Abrasives (Test Methods) – ISO 11125 Mineral Abrasive Types. – ISO 11126 Mineral Abrasives (Test methods) - ISO 11127 60. How many types of Surface Profile Comparators are being used? SHOT – S GRIT – G 61. What is abrasive’s initial particle shape and symbol as per ISO 8504-2? Type Initial Shape Symbol SHOT. Round S GRIT Angular. G Cylindrical Sharp edged. C 62. What is Mineral Abrasive? Type of Mineral Abrasives? Which ISO standards dealing with types and testing methods? An abrasive is a material, often a mineral, that is used for surface preparation purposes. There are two types of Mineral Abrasives available.  

Natural Mineral abrasives Synthetic Mineral Abrasives

*Mineral Abrasive classification comes under ISO 11126 *Mineral Abrasive Test methods comes under ISO 11127  

Natural Mineral Abrasives – Quartz Sand (Silica Sand), Olivine, Staurolite, Garnet Synthetic mineral Abrasives - Coal Slag, Copper Slag, Nickel Slag, Iron Furnace Slag and Aluminum Oxide

NOTE: Mineral Abrasive cannot be recycled which is also known as “Expendable Type”. However, in mineral Abrasive, only Aluminum oxide may be recycled with prior client approval. 63. What is the meaning of ROGUE PEAKS? isolated peak or excessive height peak, substantially higher than the surrounding peaks, normally caused by the presence of over-sized abrasive in the abrasive mixture used during blast-cleaning with grit abrasives. Rogue peaks or excessive peaks will leads to Pin-point rusting or Pin-head rusting. Lower peaks values will result in adhesion failure.

64. How many types of Blast cleaning methods available in Market? DRY ABRASIVE BLAST CLEANING: a) Centrifugal Abrasive Blast cleaning (Auto blasting machine)

b) c)

Compressed-Air Abrasive Blast Cleaning Vacuum or Suction Head Blast Cleaning

WET ABRASIVE BLAST CLEANING: a) Moisture-injection abrasive blast-cleaning (compressed-air moisture-injection abrasive blast- cleaning)

b) Compressed-air wet abrasive blast-cleaning c) Slurry blast-cleaning d) Pressurized-liquid blast-cleaning 65. Before blast cleaning, what Inspector needs to check? a) Fabrication defects b) Manufacturer’s defects c) Check Initial conditions (Rust Grades) d) Check Contamination levels (i.e. Oil, Grease, Silicone, Cutting compounds, weld smoke, bird shit, heavy dirt or other contamination) e) Check level of pre-treatment f) Check masking areas where coating or blasting not needed. Check visually for the presence of oil, grease, salts or similar contaminants. Remove any deposits of these using a degreasing or washing procedure and check whether any contaminants are still present. Mask off areas not to be blast-cleaned. Suitable methods for removal of contaminants are described in ISO 12944-4. NOTE 1 It is important that surface deposits of grease, oil, dirt and slag be removed prior to blast-cleaning, preferably with a detergent wash or clean organic solvent. If this stage is omitted, the presence of these deposits when transferred to the abrasive makes it difficult and sometimes impossible to clean the abrasive for reuse. NOTE 2 It may be advantageous to remove heavy, firmly adhering rust and scale by hand- or power-tool cleaning (see ISO 8504-3). In addition, recommendations regarding the preliminary treatment of welds, the removal of weld spatter and the removal of burrs and other sharp edges should be provided. NOTE 3 When using wet abrasive blast-cleaning methods (see 5.2), a suitable detergent may be added to the liquid to assist the removal of grease, oil, dirt and soluble salts during the blast-cleaning process. 66. ISO 11124 (Metallic Abrasive) consist of What? ISO 11124 consists of the following parts, under the general title:

Preparation of steel substrates before application of paints and related products — Specifications for metallic blast- cleaning abrasives:   

 Part 1: General introduction and classification Part 2: Chilled-iron grit Part 3: High-carbon cast-steel shot and grit

Part 4: Low-carbon cast-steel shot



67. ISO 11125 (Metallic Abrasive Test methods) consist of what? ISO 11125 consists of the following parts, under the general title: Preparation of steel substrates before application of paints and related products — Test methods for metallic blast- cleaning abrasives: o o o o o o o

􏰁  Part 1: Sampling 􏰁  Part 2: Determination of particle size distribution 􏰁  Part 3: Determination of hardness 􏰁  Part 4: Determination of apparent density 􏰁  Part 5: Determination of percentage defective particles and of microstructure 􏰁  Part 6: Determination of foreign matter 􏰁  Part 7: Determination of moisture

68. ISO 11126 (Non-metallic Abrasive) Consist of what? ISO 11126 consists of the following parts, under the general title: Preparation of steel substrates before application of paints and related products — Specifications for non-metallic blast-cleaning abrasives:         

􏰁  Part 1: General introduction and classification 􏰁  Part 3: Copper refinery slag 􏰁  Part 4: Coal furnace slag 􏰁  Part 5: Nickel refinery slag 􏰁  Part 6: Iron furnace slag 􏰁  Part 7: Fused aluminium oxide 􏰁  Part 8: Olivine sand 􏰁  Part 9: Staurolite 􏰁  Part 10: Almandite garnet (to be published)

69. ISO 11127 (Non-metallic abrasive test method) consist of what? ISO 11127 consists of the following parts, under the general title: Preparation of steel substrates before application of paints and related products — Test methods for non-metallic blast-cleaning abrasives:

a. b. c. d. e. f. g.

􏰁  Part 1: Sampling 􏰁  Part 2: Determination of particle size distribution 􏰁  Part 3: Determination of apparent density 􏰁  Part 4: Assessment of hardness by a glass slide test 􏰁  Part 5: Determination of moisture 􏰁  Part 6: Determination of water-soluble contaminants by conductivity measurement 􏰁  Part 7: Determination of water-soluble chlorides

70. In which ISO standard deals with Preparation of Welds, edges, and other areas of surface imperfections? ISO 8501- part 3

71. What are all the imperfection the inspector can reveal or find? 1. Weld defects 2. Weld imperfections 3. Weld spatter 4. Weld ripple or profile 5. Weld beads (improper) 6. Weld inclusion 7. Weld undercut 8. Weld roll 9. Weld porosity 10. Weld smoke 11. Corners 12. Edges 13. Lamination / Slivers / hackle / Pits / Craters 14. Inaccessible areas 15. Flame cutting edges

72. Under ISO 8501-part 3, what are the preparation grades available? define those preparation grades? Three preparation grades for making steel surfaces with visible imperfections suitable for the application of paints and related products are as follows: P1 Light preparation: no preparation or only minimum preparation needs to be carried out before application of paint; P2  Thorough preparation: most imperfections are repaired or corrected. P3  Very thorough preparation: surface is free of significant visible imperfections. 73. Which standards describing the Hand & Power tool requirements? Define the standards? ISO 8501 – 1 2 types of Hand & power tool standards available St-2 – Thorough hand & power tool cleaning method St-3 – Very Thorough Hand & power tool cleaning method

74. In which standard describing Flame cleaning methods? Define the methods?

ISO 8501 – 1 Fl – Flame cleaning In Flame cleaning the following standards are achievable A-Fl B-Fl C-Fl D-Fl 75. In which ISO standard deals with High Pressure Water Jetting? Define the standard? ISO 8501 – Part 4 Initial surface conditions, preparation grades and flash rust grades in connection with high-pressure water jetting

Types: Low pressure water Cleaning (LPWC) – below 5000 Psi (35MPa) High Pressure water cleaning (HPWC) – 5000 – 10000 PSI (35MPa – 70 MPa) High Pressure water jetting (HPWJ) – 10000-30000 psi (70MPa – 207MPa) Ultra-High pressure water jetting (UHPWJ) – more than 30000 psi (207 MPa) Water Jetting Standards Wa1 – Light high pressure water jetting Wa2 - Thorough High pressure water jetting Wa 2 ½ - Very Thorough High pressure water jetting 76. What is the definition of High-Pressure water Jetting? Any pressure exceedingly more than 70 MPa during water jetting 77. What are Flash Rust Codes? How many grades are available?

visual appearance of a steel surface with respect to flash rust after the surface has been subjected to water jetting or wet abrasive Blast cleaning. Flash Rust Codes: L (Light), M (Moderate), H (Heavy)

L - Light flash rust A surface which, when viewed without magnification, exhibits small quantities of a yellow/brown rust layer through which the steel substrate can be seen. The rust (seen as a discoloration) can be evenly distributed or present in patches, but it will be tightly adherent and not easily removed by gentle wiping with a cloth. M - Medium flash rust A surface which, when viewed without magnification, exhibits a layer of yellow/brown rust that obscures the original steel surface. The rust layer can be evenly distributed or present in patches, but it will be reasonably well adherent and it will lightly mark a cloth that is gently wiped over the surface. H - Heavy flash rust A surface which, when viewed without magnification, exhibits a layer of red-yellow/brown rust that obscures the original steel surface and is loosely adherent. The rust layer can be evenly distributed or present in patches and it will readily mark a cloth that is gently wiped over the surface 78. How Many Initial conditions available in water Jetting standard? DC A - A surface where the paint coating system has degraded to an extent similar to that illustrated by ISO 4628-3, grade Ri3. DC B - A surface where the paint coating system has degraded to an extent similar to that illustrated by ISO 4628-3, grade Ri4. DC C - A surface which might have been painted that has degraded to a major extent, as illustrated by ISO 4628-3, grade Ri5, or when completely degraded as illustrated by ISO 8501-1, rust grade C. DP I - An iron oxide epoxy prefabrication (shop) primer surface that has degraded. DP Z - A zinc silicate prefabrication (shop) primer surface that has degraded. 79. How many preparation Grades are available in water jetting?

Three preparation grades, designated Wa 1, Wa 2 and Wa 21⁄2, indicating the degree of cleaning, are specified.

Wa 1 - Light high-pressure water jetting When viewed without magnification, the surface shall be free from visible oil and grease, loose or defective paint, loose rust and other foreign matter. Any residual contamination shall be randomly dispersed and firmly adherent. Wa – 2 - Thorough high-pressure water jetting When viewed without magnification, the surface shall be free from visible oil, grease and dirt and most of the rust, previous paint coatings and other foreign matter. Any

residual contamination shall be randomly dispersed and can consist of firmly adherent coatings, firmly adherent foreign matter and stains of previously existent rust. Wa – 2 ½ - Very thorough high-pressure water jetting When viewed without magnification, the surface shall be free from all visible rust, oil, grease, dirt, previous paint coatings and, except for slight traces, all other foreign matter. Discoloration of the surface can be present where the original coating was not intact. The grey or brown/black discoloration observed on pitted and corroded steel cannot be removed by further water jetting. 80. How many types of water jetting available and their standards? Below 70 MPa, the techniques are called water cleaning. The NACE VIS 7/SSPC-VIS 4

standard gives two definitions of water cleaning, namely:

1. a)  low-pressure water cleaning (LPWC), which is defined as cleaning performed at pressures less than 34 MPa (5 000 psi); 2. b)  high-pressure water cleaning (HPWC), which is defined as cleaning performed at pressures from 34 MPa to 70 MPa (5 000 psi to 10 000 psi). 3. c) High Pressure water jetting (HPWJ) which is defined as cleaning performed at pressures from 70 MPs to 200 MPa (10 000 psi to 30 000 psi) 4. d) Ultra High Pressure water jetting – (UHPWJ) which is defined as cleaning performed at pressure more than 200 MPa (above 30 000 psi) 81. What is the difference between “Steel Dressing” & Surface Preparation?  

Steel dressing is also called as Steel pre-treatment (removal of weld spatter, corner, edges, and other treatment) Surface preparation is removal of mill scale, rust and old paint and creates surface profile.

82. What are all the crucial factors to be considered during steel preparation (Steel dressing + Surface Preparation)? Important factors to be considered for steel protection are:     

Treatment of steel imperfections (Steel Dressing)



The presence of surface contaminants, including salts, dust, oils and greases (Surface cleaning or degreasing)



The presence of rust and mill scale (Surface Treatment or Surface Preparation)



The surface profile

83. What factors deciding the most proper and effective method of surface preparation? Various methods can be used for surface preparation. In order to determine the most appropriate method, the contractor/designer must be aware of:

Metal condition (e.g. new or previously coated steel) Environment condition / Surroundings areas

 

Expected surface preparation grades and profiles (if any) Available equipment and personnel

  

Coating system to be applied Regulations / laws



Cost



Steel substrates may consist of new metal, previously coated metal, or shop primed metal New steel: must be checked for initial type of steel, initial rust grade,



any chemical treatment (chromating, chemicals or contaminants

phosphating),

presence

of



Previously coated steel: existing coating must be checked for generic type, adhesion, DFT, condition, contaminants, etc.



Shop Primed Steel: type of shop primer must be identified, its condition checked for mechanical and welding damages, contamination, and compatibility to subsequent coating system

Surface Preparation prior to Paint Application 

During Surface Preparation, weather conditions shall be

 

checked before starting and every 4 hours interval (or as specified) Check Steel Conditions (new or Previously Coated) If it is NEW steel, Check the Initial Rust Condition (A, B, C or D)



If it is Coated steel, Check the coating conditions as per ISO 4628 –



Part 2 to 6) Witness & Rectify Steel dressing (to remove fabrication defects and



manufacturing defects) Surface cleaning (Degreasing as per SSPC SP 1 (solvent



cleaning) Check Surface Treatment methods (Dry Abrasive blasting or Hand or



Power Tool cleaning, Water jetting or wet abrasive blasting) Check Surface Cleanliness as per ISO 8501 – 1 (Sa 1, Sa 2, Sa 2



½, Sa3) Check surface profile (as per ISO 8503- part 2 (Comparator) or

 

Part 5 (Replica Tape) Check Dust levels (as per ISO 8502-Part 3) Check Salt levels (Conductivity or Salt specific (Chlorides or Sulphates or Nitrate etc.,) SHORT ANSWER Initial condition Surface preparation methods and standards Surface profile Salt level Dust level

Masking conditions

84. How will you rectify steel imperfections? Steel Imperfections treated by Grinding 

Lamination, shelling, slivers, hackles: Remove using grinder



Weld ripple/profile: Sharp profile peaks to be smoothed using grinder Weld spatter: Remove by hammer, grinder according to specified



grade 

Flame cut: Remove rough edges using grinder to smooth and radius



the edge Sharp edge: Round to specified radius (e.g. 2mm) by grinder



Rolled-in extraneous matter: Remove using grinder

Steel imperfection may require welding 

Undercut: Weld undercuts require re-welding and grinding



Weld porosity: Treat by either welding/grinding OR enlarge the pore for paint penetration



Pits and craters: Either welding/grinding or enlarge for paint penetration

Reminders 

Weld beads, spatter and other defects must be ground to form an acceptable substrate for the paint system



Paint can’t fill blow holes Blow hole often becomes visible only after paint is applied o Will lead to initiation of corrosion by allowing moisture to penetrate o Remedial actions: Remove the paint, re-weld and grind



o

Re-Apply the paint

NOTE: Small failures like this are difficult to find, but the consequences can become big.

85. In what way steel defects will affect the coating performance? Steel defects affect coating performance Steel defects can cause three possible coating problems: 



Adhesion: A sharp edge or weld spatter can result in the coating not covering the sharp edge allowing water penetration under the film which can result in loss of adhesion after corrosion commences Wetting properties: Contamination on the surface can hinder or restrict the coating from wetting the surface and developing adhesion



Coating stress: An uneven surface (peaks and valleys) can result in changes to the surface tension as the coating cures / dries resulting in weak spots or cracking after cure

By Steel Dressing we mean removing steel imperfections (such as welding spatters, sharp edges, blow holes, etc.) through grinding or welding

86. How many types of Contamination available in steel parts? There are two types of Contamination: Visible contamination, which may include: o

Condensation

o

Dust Oil/grease

o o o

Rust and mill scale Marine Fouling

 Non-visible contamination: o

Soluble salts

87. Why should all the contamination in steel shall be removed? All contamination will create Coating Adhesion failures Example: Oil /Grease – High Surface tension Salt – Rusting or osmatic blistering Dust Marking pen / Chalk Welding smoke Inspector’s contamination



Most contamination lacks adhesion to the substrate Some contaminates such as oil/grease have a high surface tension making



paint adhesion difficult or impossible Soluble salts can absorb water from the environment (hygroscopic action)



which can lead to:  Rapid surface rusting (steel) on the treated surface 

 Osmotic blistering of the coating if applied over soluble salts All contamination will result in poor adhesion of the paint film

Dust is a contaminant and may come from scaffolding 

Spent abrasive which has not been cleaned up after blast cleaning may blow or fall into the wet paint during application, leaving a rough surface which may not be covered by the paint film and can initiate corrosion



If paint is applied over dust, a weak point is formed in the paint film, air can be trapped, adhesion is reduced and corrosion will develop rapidly 

Equipment can contaminate the Surface 

Oil contamination from pneumatic equipment (e.g. air-driven grinder) can take place if oil is leaking out of equipment, the equipment has been stored with oil, or there is a missing oil trap (air from compressor contains oil)



Must be removed prior to surface preparation

Marking Pens & Chalk can contaminate the Surface 

There are only a few types of Marker Pen recommended for inspection of steel and coatings



Paint detachment may be caused by using the wrong type of marker pen All Chalk marks must be removed from bare steel and coatings before



applying new paint   Welding smoke is a contaminant 

Smoke created by welding contains soot, burned material and salts from the



flux in the welding rods Welding smoke is water soluble and should be removed by water washing

 

If not removed, osmotic blistering of the paint may occur Solvents will not remove welding smoke sufficiently 

The coating inspector may cause contamination! 

Dirty work shoes or clothing may cause contamination inside a tank or on a



freshly prepared deck or floor Human perspiration contains soluble salts



Even a human fingerprint may in some situations be considered as contamination



Osmotic blistering occurs (after submerging in water) when paint has been applied on a surface contaminated with Water Soluble Salts

88. How many types of surface cleaning methods (to remove contaminations)? Surface cleaning (degreasing) Common Cleaning methods:    

Fresh water cleaning (preferably pressurized water) Steam cleaning Solvent cleaning Other methods agreed upon

Cleaning procedure - water soluble degreaser 1. Apply degreaser only by brush

2. Agitate/scrub the substrate 3. Clean surface with fresh water cleaning 4. Check for presence of contamination (Visual, Cloth, Water break or UV Test) Degreasing by wiping the surface with thinners and rags is not recommended. This method will spread a thin film of contamination such as oil over a wider area and the solvents increase the risk of fire or explosion.   Degreasing with alkaline detergent  

Should always be carried out before blast-cleaning After the detergents have been applied and allowed to work for the recommended time, they must be removed by ”Low pressure water cleaning (LPWC)” (around 250 - 300 bar) or higher pressures

  Removal of marine growth, salts and loose paint 

It is important to start the washing as soon as the ship is in the drydock



If the growth and contaminants are allowed to dry on the substrate they will be much harder to remove

 

Usually pressure of minimum 250 bar at the nozzle Some of the antifouling paint on ships’ hull may be removed during the



cleaning process (e.g. self-polishing antifouling) Certain types of marine growth (e.g. barnacles) will often require additional scraping or grinding to be removed

89. The usage and choice of water type during steel cleaning is important? Why and what are all the consequences? Water Quality: Potential risks from unknown sources The quality of the water is important for washing and contamination removal, otherwise additional contamination may take place during surface cleaning 

Check the source of the water, where is it coming from (drinking

water, lake or river, brackish water, desalination plants, bore-holes, etc.)?  Addition of inhibitors or other chemicals (chlorine)?  

Re-circulation, re-used water? Cleaning, filtering before re-use? Certificates or analysis?

 Potential contents: 

Salts



Contaminations Particles



 Potential paint failures: 

Osmotic blistering



“Dust” after drying, causing loss of adhesion

90. What are HAND TOOLS during pre-treatment and describe the same? Hand tools Hand tools are no longer commonly used for professional surface preparation. They require muscle power and plenty of time and patience. In return they do not give a very good standard of preparation.  Their main advantages are that they are easy to transport and are not depending on any power supply. Examples of hand tools used for steel preparation: 

Scrapers, used to remove rust and old paint

 

Wire brushes, used to remove rust Hammers, used to knock off / chip flakes and cakes of rust



Emery paper and abrasive pads, used to grind rust and old paint

91. What are Power Tools during pre-treatment and describe the same? Power tools These can either be driven by electricity or by compressed air (pneumatic). They are easier to work with and have a higher production rate than hand tools, but the quality of the output has still some limitations. Most of them are working on a rotating basis or are reciprocating impact tools. Examples of power tools used for steel preparation: 

Rotating wire brush, used to remove rust



Rigid disc grinder, used to grind away steel defects (faulty welds, spatter, delamination, etc.), sharp edges, and rust and mill scale



Flexible sanding disc, used to abrade old paint and general rust, feather edges of old paint



Needle gun, removes rust scale Chipping hammer, removes rust scale

 

Rotary impact or scarifying tools, such as Roto-Peen and Bristle Blaster, used to remove rust

Most of the power tools are hand-held portable type, but there are some larger versions as well of the “walk-behind” type

92. Please describe the advantages & disadvantage of Hand & Power tool cleaning.? Hand- and power tooling Advantages 

Simple



Good for poorly accessible areas Cheaper



Limitations 

Low productivity

 

Rotating wire brushes and disc-sanders may give a polished surface Needle gun may create high profile - hard to paint



High labour cost

Standard  

ISO 8501-1 St 2 and St 3 surface condition can be achieved Manual wire brushing is heavy work and has very low productivity



Rotating wire brushes and disc grinders speed up the production rate but increase the risk of having a polished surface



A polished substrate will result in poor adhesion of the paint

93. In Abrasive blasting, how abrasives are propelled? Abrasive will be propelled by compressed air. Auto-blasting machine - Centrifugal force Manual blasting – Compressed air Wet abrasive – Water with high velocity Water jetting – high velocity This is the most common surface preparation method for large areas. The surface is cleaned by propelling abrasive particles at high speed towards the surface to be treated. The impact of the abrasive particles will remove rust, mill scale and old coatings. The abrasive can be propelled by: 

Compressed air



Centrifugal force Water with high velocity

 

Combination of Air and Water (slurry blasting / vapour blasting)

94. What is Dry abrasive blasting? Describe their advantages & disadvantages? Compressed air abrasive blasting Abrasive is fed into a high-pressure air stream from a pressurized container through a mixing valve to a hose which is used to direct the air/abrasive mixture at high velocity from a special nozzle toward the surface to be cleaned Advantages



High productivity Creates a surface profile which can be varied



High degree of surface cleaning at high speed



   

The most efficient method of surface preparation Surface remains dry Good anchor pattern (surface profile) for paint Flash rusting avoided

Limitations 

Complex equipment



May need dehumidification of the blast air Pollution (dust, heavy metals, etc.)

  

Noise High velocity stream of abrasives is a safety risk



Does not remove salt Does not remove oil



Creates dust



Abrasive blast cleaning produces a good surface profile and several visual blasting standards can be achieved, but it does not remove soluble salts from the substrate.

95. What are all the main components of Blasting pot or Blasting hopper? Main components        

Compressed air Abrasives Blasting pot Metering valve Blasting hose Control hose Dead man’s switch Blasting nozzle

Blast pot The blasting pot is pressurised by the same compressed air which drives the abrasive. A pop-up valve at the top of the pot is opened when more abrasive is added to the pot. The pressure in the pot prevents a “blow-back” when the abrasives are gravity-fed into the airstream through the metering valve.  

96. How blasting PRODUCTIVITY affected or enhanced? Productivity In order to achieve the best efficiency, the mixture ratio of abrasive and compressed air is a key factor: 

Too much abrasive: slow efficiency, low profile and waste of abrasive

Too little abrasive: Slow efficiency as the time to achieve the required result is extended for each m² and abrasive can be wasted 

The ratio of abrasive to air is adjusted by the metering valve under the blasting pot 

Productivity is directly proportional to the pressure at nozzle: 

Pressure at Nozzle 7 kg/cm²  = 100% productivity



Pressure at Nozzle 5,6 kg/cm² =   66% productivity Pressure at Nozzle 4,2 kg/cm² =   50% productivity



97. Define Blasting Hose & Nozzle? The Blasting Hose & Nozzle



The blasting hose is made of special pressure and abrasive resistant material and can be tiring to work with due to its weight and stiffness



When extending the hose, it is important that the couplings are of approved type and without damages



To minimize loss of pressure, the blasting hose shall have a diameter which is 3-4 times bigger than the diameter of the nozzle



Blasting efficiency is limited by nozzle size, bigger nozzles consume more air Nozzles will be worn with regular use

 

Once the nozzle size exceeds the manufactures limit (normally 1 – 1,5 times), it should be replaced



Two main types of blasting nozzles: o Standard nozzle abrasive speed: 300 Km/h at 7 bar pressure o

Venturi nozzle abrasive speed: 700 km/h at 7 bar pressure

98. What is SPOT BLASTING? How is it performed in the field? Spot blasting During repair and maintenance work, some owners may specify that only corroded spots and areas shall be blast cleaned, often referred to as spot blasting, and leave intact paint untouched. However, nearby paint and all edges between blast-cleaned spots / areas and remaining paint will be damaged by stray abrasives from the blasting. The edges will be rough and clearly suffering from impact damages (punctures). Additional damages, which are not easy to see, will be small cracks in the remaining paint (microcracks).   When the remaining paint is overcoated by new paint, solvents will penetrate these cracks and cause a reduction in adhesion near these edges, sometimes also a slight lifting of the old paint. The result is that after a relatively short time the blasted spots may still look good, but the edges of the spots suffer from new corrosion (and the owner complains about a poor blasting and painting job).  

In order to avoid this disappointing result, all edges of blast-cleaned areas must be feathered by grinding equipment before being overcoated. Feathering is both time consuming and costly, so the best solution is to blastclean larger defined areas instead of many small spots.

99. What are Abrasives? Types? And standards? (Important hence repetition)?

Abrasives Abrasive types There are two main groups of abrasives used for blast cleaning:

 o

Metallic abrasives: Chilled iron grit (angular)

o

High-carbon cast steel grit and shot (angular or round)

o

Low-carbon cast steel shot (round)

o

Cut steel wire (cylindrical)

 o

Non-metallic abrasives (Mineral and slag abrasives): Natural abrasives: Garnet, Olivine, Staurolite

o

Slag: Copper refinery, Nickel refinery, Coal furnace, Fused aluminium oxide, Iron furnace

  The shape of abrasive particles influences the surface profile. Three dominant shapes of abrasive: 

Angular (grit)



Round (shot) Cylindrical (wire cut)



 Abrasive are selected to achieve the specified roughness and cleanliness: 

Particle size will define the depth of the surface profile

 

Distribution of abrasive will define the surface profile and peak density Abrasive must be free from contaminants such as oil, salt or other

 o

The choice of abrasive can also be influenced by: Type of substrate

o

Productivity required National / International laws and regulations

o

 Quality control of abrasives ISO 11124 gives specifications for metallic abrasives (Chilled-iron grit;



High-carbon cast-steel shot; Low-carbon cast-steel shot; Cut steel wire) ISO 11126 gives specifications for non-metallic abrasives (Silica sand; Copper refinery slag; Coal furnace slag; Nickel refinery slag; Iron furnace 

slag; Fused aluminium oxide; Olivine sand; Staurolite, Garnet)  Re-use of abrasives-recycling 

Metallic abrasives, can be recycled and are usually used more than once (Steel grit 20 times or Steel shot 100 times), particularly for stationary blasting machine (auto blasting machines or centrifugal or wheelabrator machines)



Mineral and slag abrasives are generally used only once and in open blast-cleaning (Expendable type)

100. What are the advantages and disadvantages of Centrifugal Blast cleaning (Auto blasting machine)? Advantages

   

Very high productivity Very little dust produced when operating in open air As the motor is electric there is no need for a compressor Cost saving in the long term

Limitations 

High initial cost

 

Complex equipment High maintenance – Worn parts



Number of wheels can limit the size and shape of treated structure

101. Please review Wet Abrasive blasting & Vapour Blasting? Methods of wet blasting Classification of wet blasting depends on how the water and abrasive is mixed: Slurry and Vapour blasting: o Abrasive and water mix together in a vessel and spray through a blasting nozzle  Abrasive injection blasting: o Water is highly pressurized and sprayed while a separate nozzle is used to inject abrasive into the water stream in front of water nozzle  Abrasive blasting with a water shroud: o A water shroud unit is placed at the end of the blast nozzle to form a water mist in front of the abrasive nozzle to wet the abrasive as it leaves the nozzle 

 Wet blasting Advantages   

Eliminates most dust Removal of soluble salts and other contamination in one process Reduces damages to adjacent areas from abrasive rebound

 Limitations     

Depending on the method selected, flash rusting can occur rapidly after blasting Inhibitor may be required to control flash rusting Not as efficient as dry blasting May be necessary to remove remaining abrasives by hosing down Disposal of water is very difficult

 Vapour Blasting 

This is the newest method of dust control for abrasive blasting



 

Water and abrasive are mixed in the blast pot in precise (computer controlled) ratios so that the water level is only enough to reduce dust and not flood the surface with water Nearly the same productivity as dry blasting Flash rusting is not an issue – residual water flashes off

 Vacuum blasting        

This equipment has a vacuum attachment which collects the spent abrasive as you blast: Equipment is usually for small repairs Several types of nozzles profiles can be used to make it possible to treat all steel profiles All types of abrasives can be used Possible to recycle the abrasives Handy size Slow production rate Environmentally friendly

102. What are the Advantages & disadvantage of UHPWJ? UHPWJ Advantages  

Removes salt and rust in one step No dust produced



No grit cost (water is cheaper in most areas) It is a noisy process, but has a lower noise level than grit-blasting



Other trades can work nearby (in the neighbourhood)



  Disadvantages 

Flash Rusting



Capital cost of equipment Less efficient than abrasive blast cleaning



No additional surface roughness (but will reveal existing anchor pattern)     

Equipment may be “bulky” for narrow spaces (ballast tanks) Water quality and availability Water freezes below 0°C Inhibitor may be necessary

103. What are RUST CONVERTORS & Usages? Do “Rust Converters” work?





Generally, you end up with a residue on the surface and that residue may itself be hygroscopic (water drawing) and may initiate osmotic blistering when overcoated Check with the coating manufacturer before allowing inhibitors to be used

There are several so called “rust converters” available: 

Phosphoric acid based (forms a layer of iron phosphate on the substrate)



Tannin based (forms a layer of iron tannate on the substrate) Penetrating oils

 

Systems transforming rust to Magnetite Systems incorporating corrosion inhibitors



Proprietary “undeclared content” (other types)



  The Australian Standard AS 2312.1 2015 states:  “The use of a ‘rust converter’ with any of coating systems is not recommended, and will detract from their subsequent performance.”

104. What is the major purpose of Surface preparation to Steel? a) To remove surface contamination b) To create surface profile or roughness c) To increase more adhesion and lifetime to the coatings 105. All non-ferrous substrate has passive oxide layer. In worst scenario if no surface preparation called by coating specification, what action would you recommend over non-ferrous substrate without blasting or other methods? A passive layer (oxide film) will develop on non-ferrous alloys and can interfere with adhesion between the paint and the substrate   A wash primer (etch primer) is sometimes used if thorough cleaning and abrasion is not possible Control of the DFT of Etch Primers is crucial as excessive thickness could result in adhesion problems of the next coat due to acid residue on the surface of the etch primer

106. Define the names of non-ferrous substrates? Common non-ferrous metallic substrates:    

Stainless steel Aluminium and its alloys Copper and its alloys Zinc and its alloys (hot dip galvanizing)

107. Why you need to paint NON-FERROUS Substrate? Define the reasons? 

Improve corrosion protection Decoration



Signage or Identification



108. Define the surface preparation methods of Stainless Steel & Aluminum? 1. Degreasing 2. Hand Abrade or Power Tool cleaning or Sweep Blasting (Follow the project specification) 109. Define the Surface Preparation methods of Copper & Its Alloys? 1. Degreasing 2. Hand Abrade or Power Tool cleaning or Sweep Blasting (Follow the project specification) 110. Define the ZINC (Galvanizing) surface Preparation methods?  Degreasing  Hand Abrade or Power Tool cleaning or Sweep Blasting (Follow the project specification) 111.

For Carbon Steel (Ferrous Substrate) which abrasives are being specified in project specifications? Steel Grit Steel Shot Garnet Copper Slag Coal Slag Aluminum Slag And other all abrasives

112.

For Non-Ferrous Substrate which abrasives are being specified in project specifications? Which abrasive shall not be used? Garnet Aluminum Oxide **Metallic Abrasives shall be not used over Non-Ferrous Substrates (i.e., Stainless steel, Brass, Copper, Bronze, Aluminum etc.,)

113.

What are the abrasive quality Test is being carried out by Inspectors at field? 1. 2. 3. 4.

Vial Test (detection of Oil and other contamination) Conductivity Test Sieve analysis (some time @ field, but generally, laboratory test only) Surface Profile yield (sample piece blasting and profile check)

5. Abrasive tossing test (unconventional or nontraditional method to check the presence of dust level) 114.

ISO 8501- Part 1 forming of how many photos? Describe those standards Vs photos? Also, which Inspection method or Tool can be used to assess the cleanliness standards Vs achieved?

28 photos

Rust Grades – A, B, C, D – 4 photos Blasting preparation Standards Photos A Grade – A Sa 2 ½ / A Sa 3 – 2 Photos B Grade – B Sa 1 / B Sa 2 / B Sa 2 ½ / B Sa 3 – 4 Photos C Grade – C Sa 1 / C Sa 2 / C Sa 2 ½ / C Sa 3 – 4 photos D Grade – D Sa 1 / D Sa 2 / D Sa 2 ½ / D Sa 3 – 4 Photos Hand & Power Tool Cleaning Standards Photos A Grade – No hand & Power Tool standards photos B Grade – B St2 / B St3 – 2 Photos C Grade – C St2 / C St3 – 2 Photos D Grade – D St2 / D St3 – 2 Photos Flame Cleaning Standards A Fl / B Fl / C Fl / D Fl – 4 Photos Inspection Tool or Technique – Use ISO 8501 – part 1 book 115.

How to measure Surface Profile? Which Standard? What instrument being used? 1. Surface Comparator – ISO 8503- Part 2 / ASTM D 4417- Method – A

2. Replica Tape (Testex Tape) – ISO 8503-5 / ASTM D 4417 – Method C

3. Electronic Digital profile Gage – ASTM D 4417 – Method B

116.

What is the inspection method to analyze the applied pre-fabrication primer is suitable for later coats? 1. Check vendor documents about pre-fabrication primer details 2. Check using MEK test (for Inorganic coating ASTM D 4752 and for organic coatings ASTM D 5402) 3. Recommendation from paint suppliers 4. Apply Test patches to decide the primer generic type

117.

Which paint shall not apply to Stainless Steel or Aluminum or other non-ferrous metals? All Zinc products (i.e., Inorganic zinc silicate / Organic Zinc epoxy)

118.

How would you assess TSA or TSZ conditions before accepting for paint? 1. The applied TSA or TSZ shall have no imperfection of flaws 2. Check for contamination 3. Check degreased conditions (By Visual or water break test or UV lamp) 4. Check any porosity or sealer requirement 5. Check type of sealer applied (i.e., Unpigmented epoxy) 6. Salt contamination check shall be made before painting 7. Check the Approved type of paint to be applied (i.e. Epoxy, Polyurethane)

Preparation of thermally sprayed metal (zinc and aluminium) surfaces Defective areas in, or damage to, thermally sprayed metal coatings shall be repaired so that the protective power of the metal coating is restored. To extend the service life of the coating, thermally sprayed metal coatings shall be painted immediately after thermal spraying before any condensation can take place. Before application of further protective paint coatings, the surface shall be treated by clause 11 in ISO 12944-4 For further information on thermally sprayed metal coatings, see ISO 2063. 119.

How to Inspect concrete surface preparation suitable for coatings? Preparation of concrete substrate vCheck concrete is fully cured vCheck moisture content / presence (test) vCheck surface laitance and other contaminations vCheck presence of oil, grease and other contamination

vPrepare the surface hand / power tool / sweep blasting vCheck the surface roughness (as specified) vRemove / blow down residues and other dust vThen apply paint or paint system 120.

How to Prepare Hot Dip Galvanized substrate before coating? Preparation of hot-dip-galvanized surfaces New Galvanized surfaces Defective areas in, or damage to, the zinc surface shall be repaired so that the protective power of the zinc coating is restored. Contamination of Unweathered hot-dip-galvanized surfaces, e.g. by grease, oil, residual flux or marking materials, shall be removed. The zinc coating may be treated by sweep blast-cleaning using a non-metallic abrasive. Other treatment shall be by the specification. After sweep blast-cleaning, the zinc coating shall be continuous and free from mechanical damage. The galvanized surfaces shall be free from adhering and enclosed contaminants that would impair the durability of the zinc coating and after applied paint systems. Examples of irregularities in the zinc coating are: • runs or overthick areas • Pinholes • Lack of adhesion between the zinc and the steel • Zinc drops • Zinc ash After sweep blast cleaning the surface shall have a uniform dull appearance. The surface roughness and the minimum zinc coating kept shall be agreed between the interested parties. Preparation of hot-dip-galvanized surfaces Weathered surfaces On weathered hot-dip-galvanized surfaces, zinc corrosion products (white rust) are formed, and contaminants may accumulate. Such surfaces shall be prepared by suitable methods selected depending on the nature and extent of the contamination. Oxidation products, certain salts and some other contaminants can be removed by washing with clean, fresh water containing detergent and by using synthetic-fabric pads with embedded abrasive, followed by thorough cleaning with hot water. Alternatively, the use of hot water, pressurized water, steam cleaning, sweep blast-cleaning or hand- or power-tool cleaning may be suitable.

121.

What recommendation is being followed by Inspector for Pollution & Environment? Recommendation about pollution and the environment Pollution caused by surface preparation is normally covered by national safety and environmental regulations. If such regulations do not exist, exceptional care shall be taken about industrial wastes, dust, noise, odours, organic solvents, etc.

Waste (such as used abrasives, rust, old coatings) shall be collected and treated by relevant national regulations and as agreed between the interested parties.