How does copper sulfate test for passivation work?
ANSWER : Chromium and nickel will not be replaced with the Copper sulfate 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.
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