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Citric Passivation Support

 

I have a customer who needs to be convinced of the effectiveness of Citric based passivation. This is a medical application, and I think citric is safer due to elimination of the possibility of chromium contamination from post process rinses. I also am pushing the "green" advantages of it. What I need is support in the way of aerospace approvals of it as a substitute to QQ-P-35C (canceled) [link is to free spec at Defense Logistics Agency, dla.mil], or any references to its' use in food or medical applications. I am aware of ASTM A967 that allows its' use. What I need is support from someone preferring its' use.

Peter Faxon
- Oxnard, California

The best support to your question is within the specifications you have sited yourself. If you look up the latest revision level to QQ-P-35 you will find that it has been CANCELLED and specifically noted within the cancellation notice is to use either AMSQQP35 [canceled] or ASTM A967 for its replacement. The document already supports your claim.

Tim Martin
plating shop - Springfield, Massachusetts

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Caution-the latest notice of cancellation, QQ-P-35C Notice 3, specifically states "Aerospace applications require the use of AMS-QQ-P-35." This specification does not allow for citric acid passivation. All other applications may use ASTM A967.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.

Wadsworth, Ohio

 

Have a look at Stellar Solutions [a finishing.com supporting advertiser]. They sell citric acid material and have a comparison of citric and nitric acids.

Nick Winstone-Cooper
- Bridgend, South Wales, UK

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Peter:

You can also refer to AMS2700, which DOES allow the use of citric formulations, as approved by the customer for aerospace use. There are thousands of companies across the world using the citric formulations because they work as well or better without the hazards. As always, there ARE some limitations as to what citric acid formulations (there are many) will do compared to the mineral acid systems. You cannot etch the surface like you do with nitric/HF formulations.

Contact us for help.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

116

 

Citiric passivation has re-kindled the debate over the best way to protect stainless from corrosion. For decades, industry has proven passivation to be 1/30th as effective as electropolishing in retarding corrosion. Plenty of pseudo-science has been passed around lately regarding citric passivation as a "green process" that "enriches chromium". In salt spray tests or fuctional comparisons, dissolving surface metal and sub-surface contamination is a proven, more superior method.

Move beyond the "chromium theories" and instead subject two processed samples to your most corrosive test. Let field results or related similar testing guide your decisions.

David Pokvitis
- Chicago, Illinois, USA