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Causes of zinc bumps on zinc plated pipes

2003

I have pipes that have been electroplated in nickel, then zinc, and finally in a chromate. When we look at the pipes we see small "bumps". It has been determined that these bumps are spherical in shape and about 10 microns in diameter and are made up of mostly zinc with trace amounts of chromium. Can anybody tell me the possible causes of these bumps?

Thanks for your help.

Tim Purdy
automotive - Greenfield, Indiana, USA

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I am personally having trouble visualizing these bumps. A 10 micron (i.e., 4 tenths of a mil) diameter sphere might be a boulder on a CD-ROM, but is a pretty darn small bump on a length of pipe. It sounds like roughness from inadequate filtration, but I can't say that I've seen quite this problem, or the problem described quite this way.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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Check the nickel plating solution for high calcium which will cause "bumps", which the zinc will bond to and plate over.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2003