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Pitting problems with 316L SST parts for filtering chloride solutions

We are manufacturing SS filtration assemblies used for filtering many pharmaceutical and biotechnical solutions, where the colution may remain in contact with inner parts for
2-5 minutes. These parts have highly buffed polished mostly on outside surfaces or sometimes electropolished inside surface too as the buffing wheel cannot reach inner surfaces properly.
We have never witnessed corrosion on our products but in one of the application where chloride solutions are filtered, the inner contact parts have been damaged with deposits and piiting has been observed only on inner contact portions only, while the outside surface remained highly polished. This has occured in just 5 months of use.
While all other vessels in contact with the same solution like huge storage tanks, pipelines other equipments also made form SS 316L only have not shown any corrosion (pitting) or very slight pitting after many years. We fail to asertain the right cause for this failure, as all results confirmed the quality of SS 316L and reccommendations to suggest SS 316L for chloride solution use.
Our question is whether SS 316L can be used for chloride solutions and what surface finish or treatment can be best suggested to improve its resistance against pitting.

Chittaranjan Sharma
Buyer - Mumbai, Maharastra, India
April 14, 2008

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Chlorides are always bad for stainless steel. 316L can many times withstand chlorides, but for the best results you may want to go to a Duplex grade like 2205, if possible.
If 316L is necessary you may want to consider periodic re-passivation, even to the electropolished surfaces, to get the highest corrosion resistance possible.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

April 16, 2008

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Thanks for the advise, We would appreciate if the details of passivation process can be advised for SS 316 and SS 316L grade.
Chittaranjan

Chittaranajn S
Filtration Products Manufacturing - Mumbai, Maharastra, India
April 29, 2008

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Hello,

Acids are a problem for the SS.
You will finish to use a plastic coat on your equipment.
Or, best, if you designe a plastic equipment for acids.

Jose Castellanos
- Minneapolis, MN, USA
June 11, 2008