Testing Passive Surfaces


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Q: What is the standard procedure for determining if the surface of a stainless steel part is passive? We would prefer a non-destructive test. J. Z.


A: The old MIL-STD-753, now AMS-STD-753 (www.sae.org), suggests a number of different tests. All of the suggested tests are destructive with the exception of the immersion copper test. A simplified version of the copper sulfate test uses a 5 g/L of copper sulfate in 5% sulfuric acid solution. Apply a drop of this solution to the surface of the part and allow it to remain on the surface for 15–30 sec. Rinse the drop off. If the surface is passivated there should not be an immersion deposit of copper.