Inspection of Galvanized Product

INSPECTION OF GAL VANIZED PRODUCTS GALV Australian Standard AS1650, Section 1.6 - Appearance (Page 5) defines the requirement for hot dip galvanized coatings as follows: The galvanized coating shall be continuous, possi ble, e, and free from defects that are continuous, as as smooth and evenly distributed as possibl possible, are detrimental to the stated use of the coated article. Methods recommended for the renovation of damaged galvanized coatings or uncoated areas are given in Appendix F (of AS 1650). Notes: 1. Defects cannot be completely quantified. quantified. When When the presence, size or frequency frequen frequency cy of any defects in the coating are considered considered sidered freque ncy con to be of concern, appropriate arrangements should be made between the purchaser and and the the manufacturer manufacturer .This may be the purchaser achieved by the provision of acceptable samples or methods of test. Where defects are present presen presentt and the product is submitted for acceptance, acce acceptance, ptance, the manufacturer manufacturer should should be able to demonstrate fitness for purpose. 2. A thicker , less smooth coating is obtained on job galvanized articles art icles compared with continuously galvanized sheet or wire. 3. (Not applicable to general hot dip galvanized products) 4. The finish of the coated object may be partly or wholly grey in colour for steels of certain composition or articles that are slowly cooled after galvanizing. Provided that such a coating has adequate adhesion, the grey finish is not detrimental, although premature staining may occur in service. 5. Advice on the transport and storage of galvanized articles is given in Appendix G (of AS 1650)

GAL VANIZED COA TING APPEARANCE GALV COATING AND DEFECTS There are a number of common types of defects arising from the hot dip galvanizing process. An explanation explanation of the causes of defects and variations in appearance follows: 1. Ungalvanized weld ar eas. Coating misses on weld areas. areas are caused by the presence of welding slag on the welds. All welding slag must be removed by the fabricator prior to despatch to the galvanizer. These areas require repair.

Unsealed welds where preparation chemicals penetrate the overlap cause blowouts which cause surface contamination and subsequent coating defects.

Welding slag left on or in welds will not beremoved by the galvanizing process and will result uncoated areas on welds.

2. Dark staining adjacent to welds. Preparation chemicals entering unsealed overlaps or through poor quality welds boil out of the connection during galvanizing and cause surface contamination and coating misses during galvanizing. Also, anhydrous fluxing salts left in the connection will absorb atmospheric moisture and leach out onto the adjacent galvanized surface. Leaching of these salts will eventually reach equilibrium. Affected area should be washed clean to remove slightly corrosive leachate. 34

Ash is a by-product of the galvanizing process that floats on the surface of the bath. Ash should be brushed off during inspection and dressing.

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INSPECTION OF GAL VANIZED PRODUCTS (CONT .) GALV (CONT.) 3. Dull gray or mottled coatings. Reactive steels will generate thicker galvanized coatings that are duller than standard coatings. These coatings have longer life because of their greater thickness and their appearance is a function of steel metallurgy and generally beyond the control of the galvanizer. 4. Dr oss pimples/inclusions. Dross is formed in the Dross galvanizing process in the form or zinc-iron crystals on (approx 95% zinc - 5% ir iron on)) with a higher melting point that the metal in the zinc bath. Dross trapped t rapped in the galvanized coating may give the coating a rough or gritty appearance. The presence of dross inclusions in the coatings is not detrimetal to the coating's performance as the corrosion resistance of zinc dross is identical to that of the galvanized coating 5. White storage staining. After galvanizing, items stored or stacked in wet, poorly ventilated conditions will react with atmospheric moisture to form bulky white zinc hydroxide deposits on the surface of the galvanized coating.

6. Ash staining. Zinc ash is formed in the galvanizing process as the work is immersed in the zinc. The ash formed is skimmed off the surface of the molten mol ten zinc prior to withdrawing the work from the galvanizing bath. Sometimes, ash is trapped inside inaccessible areas and sticks to the outside of the coating as the work exits the bath. Ash may leave a dull surface appearance or a light brown stain after removal. It does not affect the performance of the galvanized coating. 7. Striations and general surface irr egularities. irregularities. Ridges and lines thicker than the adjacent galvanized coating are caused by different rates of reaction of the zinc with the steel surface due to stress areas on the steel surface or the presence of weld areas or weld metal with modified metallurgy to the parent metal. This phenomenon is most commonly encounted on pipe and tube products.Coating performance is unaffected 8. Runs, drainage dr ainage drain age spikes and puddling. These defects are unavoidable in the hot dip galvanizing of general items and are acceptable as long as they do not interfere with the assembly of the function of the item or o r present a safety hazard in handling or service. 9. Bar e patches. Uncoated areas on the surface of Bare galvanized work are due to poor surface preparation; inadequate pretreatment in degreasing, pickling and prefluxing. These areas must be repaired using a recommended repair method or the item regalvanized if the defect is of sufficient size.

Dross pimples are formed when dross crystals present in the molten zinc are caught up in the coating, giving the surface a grity appearance.(lower appearance.(lower section). The textures and striated galvanized surface on the upper steel component is caused by the surface metallurgy of the steel producing differing micro reactive zones on the surface.



Galvanizing appearance and defects (cont) 10. Rust staining. Uncoated steel in contact with galvanized coatings will accelerate corrosion of the coating and stain the coating brown in the area of contact. This can be removed by wire brushing.

11. Delamination. Very heavy galvanized coatings (over 250 microns thick) may be brittle and delaminate from the surface under impact and require more careful handling in transport and eraction. Thin, cold rolled items with very smooth surface finish and manufactured from reactive steel may also give rise to coating delamination. 12. Black spots. Scattered black spotting is due to residual galvanizing flux crystalising on the surface of the work and is generally due to poor rinsing after galvanizing or flux contaminated rinse water. water. This defect is usually encountered from galvanizing baths using the `wet' galvanizing process where the flux is on top of the molten zinc. Excess aluminium in the galvanizing bath can also give rise to this defect.

Hot dip galvanized coatings will be stained sta ined by contact with rusty steel or timber in outdoor exposure conditions. Contact with scrap steel will accelerate local consumption of the galvanized coating. Timber staining can be avoided by using seasoned timber of the right variety.

13. Spangled coatings. Some hot dip galvanized coatings exhibit a high level of `spangling' caused by zinc crystal patterns on the surface. This phenomenon arises with galvanizing alloys produced in particular smelting processes and these alloys are commonly used for hot dip galvanizing. There is no difference in coating performance.

Industrial Galvanizers Services Industrial Galvanizers Corporation has a network of hot dip galvanizing operations operations throughout Australia and in South East Asia and the USA. The group processes over 100,000 tonnes of steel annually and offers a range of specialised services associated with the efficient provision of hot dip galvanized coatings to steel. Some of the groups hot dip galvanizing capabilities include: -

24 ho hour turnaround on on negotiated contract galvanizing.

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Heavy lif lift ga galva lvanizin izing g (e (exce xceeding ding 20 tonne onnes) s) in specific plants.

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Lar Large bath sizes in most major centre tres to accommodate long or wide fabrications

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Proje rojecct ma manage nageme ment nt capab apabil ilit itie iess to to coco-o ordin rdinaate steel to construction site.

Inspection of Galvanized Product

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