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Passivation of Stainless Steels and Titanium

 

The company I work for is in the medical implant and instrument manufacturing business. We fabricate the parts per our customer's specifications. We are currently installing a passivation system to be able to passivate the parts per ASTM F86. This is simply a 20 - 40% nictric acid bath where the parts are immersed for 30 minutes minimum. There is an accelerated process whereby the bath is heated to 120 -140 degrees Fahrenheit and immersed for a minimum of 20 minutes. According to this specification all of the implantable grades of Stainless steels and titanium can be passivated this way. Does anyone have any experience in running Stainless Steels and Titanium in the same bath, although not at the same time?

What potential problem areas may we encounter?

Is passivating these medical products as simple as they say it is?

Will we see dulling of the product?

What is the best way to test for passivation?

How do we validate the system?

Tony Spasiano
- Stamford, Connecticut, USA

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Hello Tony!

My take on F 86 is that paragraph 7.2 is a bit confusing, and SHOULD refer only to stainless steel parts. The solutions, temperatures, and times it gives are right out of ASTM A967 for Nitric 2 and Nitric 3 formulations, sometimes referred to by their old QQ-P-35C (canceled) [link is to free spec at Defense Logistics Agency, dla.mil] designations as Type VI and Type VII. Anyway, these are quite common for passivating stainless steel, and should work real well. See ASTM A967 for information on passivation inspection and testing.

These solutions certainly won't hurt the titanium- rather they won't do anything. You'll note that F 86 refers to ASTM B600 for titanium cleaning, and that steers you to fairly nasty things like molten alkali salt baths, or nitric-hydrofluoric acid mixtures. Running titanium parts through a stainless steel passivation bath might, at best, clean the titanium a little better, should you have some oils or soils that the nitric can attack.

Our stainless steel parts do not dull when we run them through the Nitric 2 bath.

You can probably contact ASTM, and get a question to the chair of Committee F04.12, who should be able to tell you their intent with the wording.

Hope this helps!

Lee Gearhart
metallurgist - E. Aurora, New York