Paint-on Coating to Identify Stainless Steel 2

[edine]

My lab has been approached by one of our vendors for a coating that when painted onto stainless remains clear and turns a coppery color for other steel grades. They had some, but lost the bottle.

Anybody ever hear of something like this?

 

[kenvlach]

This is the well-known copper sulfate test for passivated stainless steel. The Cu[sup]+2[/sup] ions in acidic solution are reduce by metallic iron, Fe[sup]0[/sup]. Consequently, immersion plating of copper occurs by an exchange reaction:

Cu[sup]+2[/sup] + Fe(metal) = Cu(metal) + Fe[sup]+2[/sup]

The solution and procedure and limitations (on which SS grades it can test passsivation & which give false positive rxn., turning coppery red anyway) are given in ASTM A967. A portion:
"17.2 The test solution is prepared by dissolving 4 g of
copper sulfate pentahydrate (CuSO4·5H2O) in 250 mL of
distilled water to which 1 mL of sulfuric acid (H2SO4, sp gr
1.84) has been added."

http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/A967.htm?L+mystore+lmnv5831

For the free version, get the old specs.
QQ-P-35C PASSIVATION TREATMENTS FOR CORROSION-RESISTANT STEEL and
MIL-STD-753C CORROSION-RESISTANT STEEL PARTS: SAMPLING, INSPECTION AND TESTING FOR SURFACE PASSIVATION,
from ASSIST:

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=50793

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=35930

 

[edine]

That sure sounds like the test except I was told the liquid was clear, not blue. Hopefully tomorrow I will get more feedback. One can only hope they have not been using a bottle of 6 year old solution for this test. Thanks.