Summary for zinc plated brass turning black Discussion
Zinc plated brass turning black is reported by Mack McPeeters on fire extinguisher hose assemblies that are plated during assembly and shipped globally, with the discoloration showing up mainly in the Middle East. He asks whether the issue is the plating or the local environment. Ted Mooney says it is hard to tell from the information given whether all parts are plated by the same vendor, but notes that corrosion is generally worse in hot, humid, salty environments than in cool, dry, unsalty ones. The thread does not identify a definitive root cause, but it points toward environmental severity as a likely contributor and suggests checking plating consistency across suppliers and locations.
Q. We supply fire extinguisher hose assemblies globally. We have recently begun having problems with Zinc plated brass components dulling and turning black in the Middle Eastern region. This problem seems to be isolated to this one particular area. The components we assemble are plated when we assemble them and any suspect components are quarantined for supplier disposition. I’m trying to determine if the problem is with the plating or environmental conditions where the product is used. Any input is greatly appreciated.
Mack McPeeters
– Greensboro, North Carolina
2003
A. Hi Mack. I don’t understand why the zinc plating of brass, but there’s a lot in the world I don’t understand 🙂
It really isn’t clear if all of these parts are plated by the same vendor or they are plated around the world, and it’s therefore pretty difficult to guess whether the plating is consistent. But certainly corrosion is more of a problem in hot, humid, salty areas than in cool, dry, unsalty areas. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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A. Perhaps…
If your problem is in an area where there are oil fields there is likely considerable amounts of sulfur
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contaminants in the environment. Much of that sulfur contaminate has no doubt become sulfuric acid which can be floating around the air in it’s gaseous state or when the air has a high moisture content as a liquid (acid rain contains high levels of sulfuric acid).
Highly corrosive, the sulfuric acid will attack the zinc plating to create zinc sulphate and hydrogen. Zinc sulphate (water soluble) in contact with copper (remember brass is a combination of copper and zinc) creates copper sulphate.
Zinc will displace the copper in copper sulphate
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A solution might be to add one more step to the plating process by plating a layer of Nickel or Chrome onto the zinc layer. The extra step is because Nickel or Chrome will not plate directly to brass, but they will plate to zinc.
Max Vision
– San Diego, California USA
May 10, 2014
Hi Max. I appreciate the input, but I can’t fully agree with it. Nickel can be plated directly onto brass, although it may be better to copper plate the brass first.
A system solution if zinc plating doesn’t hold up may be to substitute electroless nickel plating, which is very well suited to sulfide-rich environments — but it’s usually significantly more expensive.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
And thank you for the input Ted. I’m not a pro and just plate as part of a hobby. Tried nickel plating over copper on steel a couple weeks ago without the zinc layer. Can get the nickel to stick to steel and to zinc but it would NOT stick to the copper. Looks like it’s time for me to do some more research!
Max Vision
– San Diego, ca USA
May 11, 2014