Letter 8703

HOW TO PASSIVATE SURGICAL INSTRUMENTS MADE BY STAINLESS STEEL. 

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PLEASE HELP ME Dear Sir,

I am the maker of Surgical Instruments and are supplying in the local market. I have started my business in April 2000. I am using the local as well as Japanese stainless steel for manufacturing the instruments.

From the last two months, One of my customer had complained me that at the very first round of autoclave of the instruments, my instruments have caught rust, but the other test have gone well. One of my friend has suggested me that he learnt that such problems of stainless steel is dealt by PASSIVATION PROCESS. But neither me and my friend know about the Passivation process, nor we know about which chemicals are to be used.

I have in a real trouble because I am unable to selling my instruments. Yesterday I have made a search on the internet and your kind personality was appeared to me with a hope that you will be able to help me in this swear problem.

I request you to kindly guide me how I could come over to this problem and oblige me. Thank you very much for your kind co-operation and will always remind me of your great love for me.

Yours truly,

SULTAN MEHMOOD
- SIALKOT, PAKISTAN

Hello Sultan!

Passivation is a process in which you remove stray iron particles from the surface of stainless steel, and/or enhance the formation of the chromium oxide layer that makes stainless steel resistant to corrosion. It is commonly done in nitric or citric acid formulations.

The first thing that you want to do is go to Finishing.com's home page, and look in the Frequently Asked Questions area- that's Section 4. There is a FAQ on Passivation of Stainless Steel that is worth reading.

Another source of information is the US Federal Specification QQ-P-35C [link is to info about spec at TechStreet], which you can get free from http://assist.daps.mil. Click on the Quicksearch button, and type in the "QQ-P-35", and it will get you the document in pdf. It lists only the nitric acid formulations. Several citric acid recipies are given in ASTM A-967 [link is to info about spec at TechStreet] (available from the ASTM at astm.org) and in AMS 2700 (available from the SAE at sae.org).

I hope this helps!

Lee Gearhart
- East Aurora, NY USA

Dear sir,

By saying "passivation" I believe you mean the thin protective coating film formed on the articles.They are primarily chromium oxides(Cr2O3).We require a minimum level of 12%Cr to ensure a passive layer. Your query does not indicate the "grade" of stainless steel you have used. I feel "austenitic" stainless steel is the best choice. If you have already used this grade then the problem could be some thing else for which I need the exact description of the "corrosion" pattern and how it looks like on the instrument...

Regards,

C.K.Sekar
- Chennai, Tamil Nadu, India

Sulton:

Much of the surgical instrument industry has gone to using CitriSurf products for passivation. These instruments are commonly 410ss or similar, with laser etching. The laser etching is a very weak point in the corrosion problem and must be passivated to pass the autoclave tests.

The trick is to get the passivation required without removing the laser etch marks that the manufacturer wants to remain. This can be attained with a significant improvement in corrosion resistance over the old nitric acid methods layed out in QQ-P-35c.

Contact us if we can be of assistance.

Regards,

Lee Kremer Stellar Solutions, Inc. Algonquin, IL, USA

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