Zinc Embrittlement

Date 02-15-2006 13:39

Zinc Embrittlement, Liquid Metal Assisted Cracking (LMAC), Liquid Metal Embrittlement (LME) and Solid Metal Embrittlement (SME) of autentic stainless steel by zinc is well documented. The best practice would be eliminate galvanized of zinc plated steel around the Stainless Steel. The biggest problem I have seen has been where someone errected Austentic Stainless Steel Piping with Galvanized Pipe Hangers.

Zinc, galvanizing has very limited use in refinery except for some compressed air lines and pipe hangers. Though zinc rich paint can case the same problem.

If you can not replace the zinc that is near the Stainless steel, coat it with a good quality epoxy paint.

By - Date 02-16-2006 00:31

In my opinion, there are far and few in between instances where painting of SS piping is acceptable due to the high probability of entrapment of foreign particles that can embed into the microcrevices of the SS, thus causing the possibility of intergranular stress corrosion. Careful precautions must be taken if it is absolutely determined to paint the SS.

By CHGuilford (****)

Date 02-15-2006 17:26

I'm thinking RBeldyk's response is probably your best bet. In fact, you could also paint your stainless piping, although I thinking most plant managers won't like that idea.

Not meaning to be a smart aleck, just don't know the application, so I'm wondering: If you had a fire that was hot enough to melt the zinc on galvanized steel, what condition would you expect the stainless to be in afterwards?

Chet Guilford

By jon20013 (*****)

Date 02-15-2006 18:31

Chet;

I think theres many stainless steel experts in this forum who might agree with the plant managers. Painting stainless steel is not a good idea!

By CHGuilford (****)

Date 02-16-2006 17:37

That's why I said that. Not that it is a good idea but it is possible to apply a coating, or shield, or barrier to the stainless; even fireproofing could be done. Again, not a good idea but physically possible.

The other part of my response was: if you have a fire that melts the zinc off galvanized pipes or structural steel, I think the stainless piping might be a lesser percentage of the damage costs. If the stainless is such a critical concern, I would hope the design would be such that zinc could not get on the stainless in the first place.

Chet Guilford