How Does copper sulphate Test for Passivation Work?

A. Chromium and nickel will not be replaced with the copper sulphate test solution (which also contains sulfuric acid), only the Fe or other less noble metals. If there is free iron on the surface it will be replaced by the copper, forming the distinctive copper color on the surface in this 6 minute test.

Of course, this test should only be used on austenitic stainless steel. Some people use it on other grades, but you can get false failures.

A. Hi Chris. It's possible that you are misinterpreting the chart. Platinum and Gold are on the noble end of the seawater series, magnesium is on the active end. Nickel and chromium are closer to platinum than steel is.

Regards,

A. To answer John's question, I'd look up a standard test and use that, rather than make my own. Primarily because I'm lazy, but you can also argue that something published by a known organization probably has had some thought behind it, maybe it's been vetted as well.

So I'd go to Assist Quicksearch by typing that into Google and hitting "I'm feeling lucky". Then I'd type "753" into the number box, and click on the icon that will display MIL-STD-753 [on DLA / cancelled] revision C [replaced by AMSSTD753]. Then I'd read that one, and if it met my needs, I'd use it.

A. If you need instructions / information look up ASTM A380 section7.2.5.3 copper sulphate test.

A company that makes and sells kits for this is Koslow Scientific Company in Englewood, New Jersey.

A. copper sulphate solution is a saturated solution. It should be kept fresh.
Be sure to carefully remove all of the copper deposits. This is a slightly destructive process.
Koslow Scientific company sells a color spot test kit that does not require any mixing of chemicals. It is called the Passivation Color Kit 1626. The color reaction takes place not on the metal surface but on a sensitive test paper.

Hi Randy. It's an interesting question, but I'm not sure that it's worded quite clearly enough.

I should think that anyone who can safely perform a passivation test is welcome to perform one, but that we can't put much credence in their results if we don't have reason to trust their qualifications :-)

Can we have the situation? Thanks!

Regards,

A. Randy,
The question is, is it a requirement by whom? The ASTM and SAE standards on passivation don't say anything about certification. If your customer asks for A2LA though, then you need to have it.

A. Good day Angel.

If you are passivating in the nitric based solutions, give the parts a dip in the passivating solution. Keep this solution off line for this purpose only, to avoid contaminating the process solution with copper.

Regards,

A. Angel,
Sodium persulphate with a little bit of acid in it makes a good copper stripper that isn't very hazardous to work with.

A. We've talked already about this, but I will answer here also for the benefit of other readers.

First I will note that chrome plating and electropolishing are very different things.

Chrome plating is not normally done with stainless, and if it is, I see no reason to passivate or run a passivation test because the stainless has been covered over. copper sulphate is often used to check for gaps in plating over carbon steel though.

Electropolished stainless can be citric passivated for extra good corrosion resistance, at which point it's certainly fine to run copper sulphate testing in order to comply with the relevant standards. If you don't have to comply with the standards, then it's pretty much up to you.

A. Juan,
The copper sulphate test as far as I know originated in MIL-STD-753 [on DLA / cancelled], and probably will still work fine if the amounts are slightly off, though you would still be "out of spec" for using it.

A. Eric,
Copper is fairly toxic to living cells. In theory, a stainless part passing the copper sulphate test will have no residual copper and will be safe for medical use. However, the attitude in the industry is that nobody wants to undertake the task of proving this is a reliable certainty, therefore ASTM F1089 requires that any medical instrument tested with copper sulphate be disposed of. Personally I think there ought to be other practical ways around this, but if you need to be compliant to F1089 that is the rule.