Stainless Discoloration

[HAWK]

Heh Guys,

Is this what you are talking about on the stainless being discolored after welding?

[HAWK]

No replies? Is the the type discoloration we are trying to clean up?

[illuzion]

Yes this is one way I have seen it manifest, It is often very blue in color, and occurs right around the affected heat zone. I'm not sure, but I believe the procedure to fix this is called passivation, as it also prevents the stainless from rusting. There appear to be 2 methods of removing this, the first is 100% chemical, and involves a paste, which is acid based, and highly caustic, which can remove the discoloration. The preferred method seems to be electrochemical, which involves a reverse electroplating process. I have seen a few manufacturers advertising equipment with prices ranging from $600-$3000 from various companys such as walter, dynaflux, and chemclean
-illuzion

[HAWK]

illuzion,

I have heard of an electrolysis process using a mild acidic solution to remove this coloring and blend the filler with the surrounding material. I ran this with a 309SS 3/32" electrode. The plate base metal is 1/4" A304 SS. The tube is of the same material in a 3" schedule 10. I ran it quite hot and washed the toes quickly.

The attached picture is TIG welded SS. I do not know what the base material specs are. It was done some years ago as you can tell from the picture. Note know how well the welds (strictly fusion) match the material. One of the reasons is the cooling action during the welding process: This cube is filled to the top with tap water.

I am just wondering if you were able to pre cool your base metal if the discoloration would not be present? The other variable here is these SS welds are fusion only-no filler. I beleive there are 2 factors in haveing the discoloration: Heat input and filler properties. In this picture both are eliminated.

What do you guys think? Any ideas? Agree? Disagree?

The attached picture is a zip file and then will open with Adobe Acrobat 5.0 and later.