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Increasing corrosion resistance for 316 stainless steel. How?

I have an application of a plumbing valve that uses 316 stainless steel. It is to be used in a toilet sanitary system in an aircraft with an extremely long life expectancy.I want to increase the life expectancy against corrosion by water and common drain cleaners. I already passivate the valve. Any suggestions for coatings/treatments to increase resistance to corrosion?

Thanks,

Jack Howerton
aerospace - Naples, Florida

Plate the part with high phosphorous electroless nickel.

Dan Weaver
- Toccoa, Georgia

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Electropolish it. Electropolishing is the most effective passivation process there is, plus the extreme smoothness that is imparted will be ideal for this application.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
 

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Hi phosphorus electroless nickel plating (about 1 -1.3 mils) would improve the corrosion resistance considerably.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
 

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Jack:

The ultimate in chrome oxide ratio and corrosion resistance that we have seen is to electropolish the part and then passivate it with proprietary citric acid formulations. In tests, this proved to be the most effective long term in corrosion resistance. High phos EN is also excellent in corrosion resistance. If you cannot go through these processes, let us know and we will teach you how to get the best passivation possible with standard passivation. I assume that you have some welds to contend with in the toilet unit. This is the weakest area of the unit and they need to be treated properly to get what you want.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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PVD coating is a very good way to get better corrosion resistance.

Thanks.

Sheron Wen
- West St Paul, Minnesota, USA

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All of the above suggestions are good, but in addition require your steel supplier to provide very low sulfur 316.

Sulfur content should be less than 0.002%. Corrosion in 316 begins with pitting and pitting originates at sulfides. That is why the surface treatments recommended above are effective. They remove exposed surface inclusions.

Dr. Michael McGuire
- Pittsburgh, Pennsylvania, USA

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Dr. McGuire,

If you have a barrier of EN, how does the sulfur content effect the corrosion resistance of the valve?

Michael McLaughlin
Pulp and Paper - Queensbury, New York, USA