How to test passivation of stainless steel parts

A. Dear Maricela,

The easiest way to test your passivation, is to test how much free iron is left after passivation. You can dip your item in, say, 100 ml 1% phosphoric acid, and measure how much iron has the acid dissolved after 3 minutes. That will give you a good idea about your passivation.

Best regards,

A. I suggest you to use copper sulphate ⇦this on eBay or Amazon [affil links] Test. Prepare a solution as follows.

Distilled water: 250 CC
CuSO4 (copper sulphate )- 1g
sulfuric Acid (1.84 sp. gravity)- 2cc

Pour Acid into water and dissolve CuSO4 in it. Apply the solution on the surface to be tested. If free iron is present, you will see copper deposits on the surface.

A. Remember that the copper sulphate test can give false positives with martensitic and ferritic stainless steels. If you have the budget to buy a document, get a copy of ASTM A967 on passivation. It lists several tests that are appropriate. As a free yet not as good alternative, you could also download a copy of the cancelled (yet still interesting reading) MIL-STD-753 [on DLA / cancelled] on Passivation Testing [ed. note: replaced by AMSSTD753]

A. I have found the kits and testers from Koslow Scientific Co. a very effective detection of passive film.

A. Keith,

The copper sulphate spot test indicates the presence of free iron on the surface of the steel. If there is no free iron prior to passivation you will not get an indication.
If you want to see if the solution works, try applying it to some mild steel, you should see a reaction in seconds!

A. Hi Surya. We appended your inquiry to a thread where Rajesh Ravindran offers the test procedure and Brian Terry suggests spot testing mild steel with it to verify that you get a deposit of copper. Good luck.

Regards,

A. So I dug into this because we started a passivation line to keep work in-house. After machining 300 series CRES, I did not get an indication using the copper sulphate solution. I tried several things to get a positive indication, even sanding it wet with acetone to ensure the solution would wet out a fresh surface, but found that only after hitting my test piece with a carbon steel wire wheel, would I get an indication at that location. So generally there is not enough free iron on 300 series CRES to give an indication, but a machining operation might leave free iron behind and that could make the surface active enough to increase the corrosion rate in harsh environments.

Note, after getting this indication, I repassivated the test panel and found that the passivation solution (we are using Stellar Solutions [a finishing.com supporting advertiser] CitriSurf 2450) does not remove the Copper indication. That must me removed with abrasive methods before applying the passivation solution.

Hope this helps,

-Kirby