Some common defects may arise during hot dip galvanizing process. There are several reasons for the causes of such variations and defects to take place.
Galvanized Coatings: Some defects
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Ungalvanized weld areas: The weld areas may have some coating misses which could be due to welding shag being present on the welds. The fabricator is required to remove the welding slag before it is delivered to the galvanizer.
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Mottled or dull gray coatings: Thicker galvanized coatings will be generated by reactive steels which are dull when compared to standard coatings. Such coatings tend to have longer life due to their greater thickness. Moreover, their appearance is steel metallurgy’s function, which is beyond the galvanizer’s control.
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Dark stains present adjacent to welds: Unsealed overlaps may witness preparation chemicals entering them or poor quality welds simply boil from connection during the galvanizing process. This will only cause coating misses and surface contamination during galvanizing. Moreover, anhydrous fluxing salts remaining within the connection are likely to absorb atmospheric moisture, while leaching onto adjacent galvanized surface. Such salt leaching will each eventually the equilibrium. It is necessary to clean wash the affected areas for removing those slight corrosive leachate.
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Inclusions/Dross Pimples: During galvanizing process, dross is generated as zinc iron crystals or in the form in higher melting point when compared to metal in zinc bath. Galvanized coating experiences trapped dross which gives out that gritty or rough appearance to the coating. Dross inclusion presence in coatings will not be found to be detrimental to performance of the coating, since zinc dross resistance is identical, similar to that of galvanized coating.
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Ash staining: During the galvanizing process, there is formation of zinc ash, since it is in zinc that the work gets immersed. The ash that is generated gets skimmed off the molten zinc surface before withdrawal of the work from galvanizing bath. At times, ash can be found to be trapped within the inaccessible areas, while sticking to the external part of the coating, when the bath is exited by the work. A light brown or dull surface stain is left by ash after removal. However, the galvanized coating performance is not affected in any manner.
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White storage staining: Once galvanizing is completed, the items stacked or stored in poorly ventilated, wet conditions will become white bulky zinc hydroxide deposits upon the galvanized coating surface due to atmospheric moisture reaction.
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General surface irregularities and striations: Lines thicker than adjacent galvanized coating and ridges may appear due to varying zinc reaction with steel surface. This is more due to the stress areas upon the steel surface or probably the welds presence or weld metal that is modified metallurgy into parent metal. It is regarded to be a common phenomenon faced with tube and pipe products. However, coating performance is not affected in any manner.
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Bare patches: The uncoated areas of the galvanized work surface are because of inadequate pretreatment in pickling, degreasing, pre-fluxing and poor surface preparation. It is necessary to get the areas repaired by making use of recommend repair procedure or regalvanize the item, if defect is found of sufficient size.
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Puddling, drainage spikes and runs: They are termed to be unavoidable defects in general item hot dip galvanizing process. They are acceptable unless the function assembly of the item is not affected or safety hazard present in service or handling.
The above are stated to be the few of the reasons for defects to appear in galvanizing and amazing solutions to it.
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