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Black spots from storing galvanized parts in pickling area

Q. The storage area of our galvanized fastener is nearby to the pickling area, around 100 meters. We have found that a few days after galvanizing, small small black patches were found on a few concentrated areas of the bolts. Is environmental condition the issue behind this?

Kirt Shar
galvanized fasteners - vizag, andhra pradesh, India
September 24, 2015

User's Guide to Hot Dip Galvanizing for Corrosion Protection in Atmospheric Service
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A. Hi Kirt. It's probably not possible to say that the storage conditions are the only problem or the chief problem when we know little else ... but it is certainly right to say that pickling fumes, even in low concentration, will very rapidly attack galvanizing, so that storing galvanized parts in the vicinity of galvanizing fumes is a recipe for ruining them.

Remember that zinc is very rapidly and severely attacked by acid. Good luck.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2015

Q. Dear sir,
Thanks for your reply. We have maintained all the parameters as well. Also the surface finish is good too after being galvanised. Still the problem is being faced by us.
One more problem being faced is that the nuts after getting tapped are developing a very dull look. A few dark patches are observed too. We are using proper lubrication. What might be the reason for this?

Kirt shar
galvanised fasteners - Vizag, A.P, India
September 24, 2015

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