Galvanizing & Corrosion Quiz Hot Dip Galvanizing & Corrosion Fundamentals 1. The standard normally specified in Australia & New Zealand for hot dip galvanizing fabricated items is: AS 4312 AS 2312.2 AS/NZS 1214 AS/NZS 4680 2. Which of these processes would usually provide the thinnest zinc coating: Thermal metal spray Continuous sheet galvanizing Batch hot dip galvanizing Electroplating 3. The four essential features of any corrosion cell are: Anode, cathode, oxygen, moisture Anode, cathode, electrolyte, conducting path Anode, cathode, oxygen, conducting path Oxygen, moisture, steel, copper 4. Which of the following is not a good design feature to help minimise corrosion: A structure which allows easy painting A structure with crevices and cavities A structure with drain holes A structure with good ventilation 5. The life of a galvanized coating over steel mainly depends on: Coating thickness and exposure environment Grade of steel and coating thickness Method of application and coating thickness Method of application and exposure environment 6. Hot dip galvanizing provides a very good corrosion and impact-resistant coating but should not be used where the coating is subject to: Acid or strong alkaline conditions An epoxy top-coating Organic solvents A rural environment 7. A micron is: One thousandth of a metre One thousandth of a centimetre One thousandth of an inch One thousandth of a millimetre 8. According to AS/NZS 4680, the minimum average coating thickness applied to a non-centrifuged article with Si > 0.01 % and 8 mm section thickness must be at least: 100 microns 125 microns 85 microns 55 microns 9. Compared to batch hot dip galvanizing, sheet, strip or in-line galvanized products would have: Similar zinc coating thickness and durability A thinner zinc coating but improved durability due to absence of alloy layers Greater zinc coating thickness and better durability A thinner zinc coating and reduced durability 10. Compared to batch hot dip galvanizing, zinc thermal spray has the following feature: Better appearance but reduced durability because of alloy layer formation Much better performance in submerged and underground environments Limited to sheet steel No limit on section size 11. Abrasive blasting may be specified before galvanizing: To obtain a smoother and brighter finish To provide a thinner zinc coating If the item is to be painted after galvanizing To provide a thicker zinc coating 12. The main purpose of the hot alkali (caustic) treatment before galvanizing is: To reduce internal stresses and likelihood of distortion To remove rust and mill scale To remove oil, grease and related contamination To protect steel from re-rusting before dipping in zinc kettle 13. The main purpose of the acid pickle treatment before galvanizing is: To remove rust and mill scale To protect steel from re-rusting before dipping in zinc kettle To remove oil, grease and related contamination To reduce internal stresses and likelihood of distortion 14. The most common chemical used for pickling is: An aqueous sodium chromate solution Zinc ammonium chloride Hydrochloric acid Sodium hydroxide (caustic soda) 15. The main purpose of the fluxing treatment before galvanizing is: To remove oil, grease and related contamination To remove rust and mill scale To activate the surface and protect steel from re-rusting before dipping in zinc kettle To reduce internal stresses and likelihood of distortion 16. The usual chemical used for fluxing is: Heated sulphuric acid Zinc ammonium chloride Hydrochloric acid at room temperature An aqueous sodium chromate solution 17. The typical temperature of the galvanizing kettle is approximately: 500 °C 650 °C 450 °C 250 °C 18. Progressive dipping is usually carried out: To prevent the formation of wet storage stains To obtain a coating of twice the thickness To more thoroughly clean the item When the item is too large to fit in the bath in a single dip 19. One of the recommended methods for repair of small bare spots in a galvanized coating is: 100 microns of zinc-rich primer Strip the coating and re-galvanize A spray of ‘Cold Galv’ Two coats of aluminium paint (‘Silver Frost’) 20. Wet storage stain normally arises due to: Galvanizing items with insufficient drainage holes Insufficient pickling during surface preparation Application of a galvanized coating that is too thin Storage or transport of newly galvanized items under moist or humid conditions 21. Wet storage stain also showing red rust: Should be treated as for bare spots and repaired using zinc-rich primer Is not a cause for concern or rejection Should have the wet storage stain brushed off and red rust treated with a rust converter Should have both wet storage stain and red rust brushed off and left as is 22. A hot dip galvanized coating normally consists of: A pure zinc layer with an outer layer of iron-zinc alloy Tiny particles of pure zinc surrounded by a matrix of silica Iron-zinc alloy layers with an outer layer of pure zinc A layer of pure zinc 23. The most important elements in the steel influencing coating thickness and appearance are: Silicon (Si) and phosphorus (P) Nickel (Ni) and chromium (Cr) Silicon (Si) and sulphur (S) Iron (Fe) and carbon (C) 24. A galvanized coating on a steel with a silicon content of 0.4 % will be: A thin coating with a dull grey appearance A thick coating with a dull grey appearance A thin coating with a bright, shiny appearance A thick coating with a bright, shiny appearance 25. Hydrogen embrittlement of galvanized steels: Is a significant risk in progressively dipped items Is only likely with ductile steels Is only possible with high strength steels (tensile strength > 1000 MPa) Can arise due to significant cold working or shearing before galvanizing 26. The galvanizing Inspector should: Read, understand and clarify all aspects of the client’s specification Be aware of the requirements of AS/NZS 4680 and AS/NZS 1214 Know their responsibilities and duties regarding the work All of the above 27. The galvanizing inspector must not: Make changes to the specification Read, understand and clarify all aspects of the client’s specification Ensure conformity with the specification Observe, test and report all relevant aspects of the galvanizing process 28. If the galvanizing inspector notices major welding defects in a fabrication, they should: Make notes and point out to the Client and Galvanizer Make arrangements with the fabricator to get them repaired Ignore them, unless this is specifically part of your job description Ignore them, as the zinc will adequately protect such defects 29. It is a good idea to obtain the chemical analysis certificate for the steel to be galvanized because: The alloy content indicates the method of weld repair that can be carried out The silicon and phosphorus content will indicate the expected appearance and thickness The carbon content will indicate the colour of the work after galvanizing The sulphur content will indicate the PPE required when observing the work 30. Venting of enclosed items to be galvanized is required to: Allow air and gases to escape to avoid explosions To keep the air clean within the galvanizing plant Meet the EPA requirements of galvanizing plants in built-up areas To allow escape of noxious fumes during pickling 31. Items to be hot dip galvanized may require vent and drain holes: To allow rain or condensation to drain from the finished item To ensure maximum coating thickness For easier handling of the items when dipping To allow draining of acids and zinc and to avoid explosions during processing 32. Distortion during galvanizing is most likely in which of the following: Items that fit into the zinc bath Large items that require progressive dipping Circular, square or rectangular hollow sections Assemblies of equal or near equal cross section thickness 33. Welding slag on an item to be galvanized: Must be removed only for items with a section thickness less than 6 mm Should only be removed when the client’s specification requires as it’s an appearance issue Must be removed by the fabricator before galvanizing Can be left by the fabricator as it will be removed during the caustic cleaning process 34. Ash deposits on a galvanized coating:
