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White spots in the inner side of pipes

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Q. We are facing a problem in galvanising pipes. Some white spots are present in the inner side of the pipes. Please suggest us what to do.

Shahzad Yasin
Director - Lahore, Punjab, AND Pakistan
2007

A. Sir:
I have worked for many pipes galvanizers and have never experienced white spots on the inside of the pipes. If you are having this problem in one plant only, then it could be many things including: 1)Too much aluminum in the zinc, 2)Ash inclusions entered at take-out, 3)Something in the flux, 3)Contaminated quench water (particularly chromate quench with too high of pH), 4)Contamination of the blow steam, 5)Dross pick-up, 6)Many other factors.
If you could describe these white spots, e.g. small, large, circular, blotchy, etc. it would be helpful to identify them. Also the zinc bath analysis would be useful.
Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA

adv.
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