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  for Metal Finishing since 1989
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Problems with Tube Nuts

2000

We have a problem with some tube nuts. The nuts are low carbon steel. The old system was to zinc plate the nut, add a yellow (yes, hexavalent) chromate, then coat the nut with an organic aluminum-rich paint. The nut is then put on a plated low carbon steel tube and then tube is endformed.

We have two problems right now. The paint gunks up the threading on the nut so that it can not be screwed in. Also, the nut has problems passing corrosion testing requirements (cyclic testing). We are thinking of going to just zinc nickel with yellow or bronze chromate or making the nut out of brass or stainless steel.

My thought on using another material is that we will create galvanic corrosion from dissimilar metals and even though we solve our nut problem, the tube will start seeing problems. I don't know if zinc nickel would be good or not.

Let me know what you guys think. I am looking for some educated comments, but nothing too in-depth. This is just free chat. I am also looking for general solutions, not a sales pitch for a particular product. Thanks!

Tim Neveau
Rochester Hills, Michigan

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I think that a mid phos EN would work very well for the application.

If SS were cheaper, I would do some testing. nickel zinc would come close to your plate and paint scheme price and do it cheaper.

James Watts
- Navarre, Florida
2000