Metal finishing Q&As since 1989

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SS Weld is discolored

We are into expansion bellows. We weld thin sheets of Stainless steel into tube and then the same is welded with flanges. During the welding with TIG we get a reddish/light blue area at the point. We want to have a pure white line as similar to the parent material. Can you advise us how to clean this welding area.

RAJESH RATHI
- Kolkata, W.B
2006

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2006

Dear Rajesh,
Cleaning and Passivation of stainless steel has till recently been a method which utilizes mineral acids or its salts.There usage is limited to surface iron.This method re deposits surface iron very quickly that the surface starts looking rusty soon.
Stainless Steel is comprised of a mixture of primarily iron,Cr,Ni and other material blended uniquely to give special properties to SS.During welding, because of excess heat generated,the percentage of those mentioned above changes and more iron surface on the top layer giving a rusty look.
You may first remove welding scales and rust by using an effective scale remover and then passivate the surface from re-deposition of removed free iron.
There are products(SS passivation) now available to give the result you are looking for.One such company manufacturing these products are, Surtec International USA and I understand they have representation in India too.
Best of Luck.

T.K. Mohan
plating process supplier - Mumbai, India