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Can Citric or Nitric Passivation Be Done on Both Series 300 and 400 Stainless?
November 5, 2012
Q. I work in the medical device industry and my firm is currently reviewing our passivation procedure. We are referencing ASTM 967 and would like to use the chart in the ASTM as a guide, but not a mandatory requirement. Would it be a correct statement that all 300 and 400 series SS and also 17-4 can be passivated using any of the Citric or Nitric processes? The ASTM seems ambiguous in the fact that it doesn't define specifically what process to use but to use it as a guide. Thanks!Shawn Tribolet
- Warsaw, Indiana
A. SS300 & 400 can be passivated by pickling with heating nitric acid 72 degree baumé as concentrated using chromic acid @ 1% on total volume (which acts as an INHIBITOR). If you are using citric acid you should use (EDTA) based INHIBITOR. THE INHIBITORS using avoids hydrogen embrittlement, resulting in good corrosion resistance. Both citric acid/Nitric acid are also has to be heated for 15 to 30 minutes to get perfect passivation. Using Nitric acid is best.C PRAKASHAM
CONSULTANT- Chennai, Tamilnadu, South India
For nitric passivation, you very much should pay attention to the chart used by ASTM A967 / AMS 2700 / QQ-P-35. Bad combinations of bath formulation and stainless grade can result in destroyed parts and/or runaway reactions producing clouds of toxic gas.
Citric passivation is much more forgiving. A low pH bath can sometimes cause some light surface etching to non-300 grades, but a citric bath with a raised pH is generally good for all grades.
Let us know if we can help.
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I don't think you are familiar with passivation or are using the word inhibitor properly.
Stellar Solutions, Inc.
A. The problem of medical parts passivation can be solved easily by switching to alternative passivation technique. It is hard to persuade people to alter their existing methods.
We are giving away (for small fee) one of such passivating electrolytes with the condition that the receiver of such process will keep it confidential, and provide the testing results and his opinion on this web site. Contact me if interested.