Are passivation test kits gimmicks?(2004)
Has anyone ever heard of or used a passivation testing kit? Supposedly it's supposed to eliminate all the other testing of passivation (humidity, salt fog, Cu sulfate, ferricyanic) and is approved by the federal method QQ-P-35C [link is to free spec at Defense Logistics Agency, dla.mil]. I was just wondering if it was just another gimmick.Delia Heffernan
plating shop - Lenexa, Kansas, USA
Which kits are you referring to? I have a Koslow tester and if you understand passivation, it is an effective tool.
I find passivation is much more than a yes/no proposition. There are degrees of passivation. The trick is to match the level of passivation to the corrosive environment. For example, mechanical polishing of the HAZ of welds is sufficient for many industrial applications. For more corrosive environments (even in the same plant), a subsequent citric passivation is required. In some instances, the condition may require full electropolishing as premium passivation.
The chrome oxide film wants to reach a state of equilibrium. One metallurgist told me stainless steel is either becoming more passive or less passive. A Koslow tester will indicate those trends. His explanation was a bit deeper than I could really get my arms around, but it made sense.
Do you have other passivation testers available? I've heard of other proprietary passivation testers being developed but am only familiar with the Koslow device available commercially.
Beyond kits, we have ASTM recognized test methods such as copper sulfate and ferroxyl. I like copper sulfate best as the ferroxyl seems much more touchy based on the application.
I hope this helps.Todd Turner
- Monroe, Louisiana
Todd's answer is right on, but I would add one additional item for consideration. None of these tests is any true measure of passivation. The passivation kit testers, like Koslow's, and the ASTM test methods like the ferroxyl and copper sulfate tests, only test for the presence of ferrous surface contamination. They provide no indication of the soundness of a passive surface film on the stainless steel. The humidity and salt fog tests will provide some qualitative indication of true passivity.
IMHO, the Koslow tester is a nice tool for quick evaluation of ferrous surface contamination. Faster and easier than the ferroxyl and copper sulfate tests, but no more effective.
I know of many tests for passivation that are being used in the industry, most of which are not formal tests in the standards. It is best to stick to the standard tests that you see in the ASTM or AMS standards.
There are some new passivation testers available in Europe that may be worth trying, but in general the "quick test" devices provide spotty results and can mislead you many times. This is why they have not been put in the standards. They are good for collecting comparative data maybe.
Stellar Solutions, Inc.
April 22, 2010
The Koslow Tester not only detects the presence of surface free iron as does the ferroxyl test but also can detect if the invisible chrome oxide layer is in tact. We run the tester over all our stock.Laurne Keane
- Tenafly New Jersey
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