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  for Metal Finishing since 1989
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Question regarding the differences between 316 and 316L

Dear Friends,
I was reviewing the letter 14356 which honestly is somehow part of my question. I am a mechanical engineer and not a material expert, but we have a problem regarding selecting 316 and 316L. As a matter of fact although we know that somehow stainless steel is not so suitable material regarding the chloride service but our people has selected this material for a pump with 250 mg/l chloride content in water. The pump is a spray water pump to cool down the temperature of our aircooled heat exchanger. Now our material people stuck on the chloride content which the above mentioned amount is based on the worst case when it happens vary rare case because of the plant problem on chlorination system. Anyway I would be appreciated to have your kind advices and instructions that whether we have such a big deal on this issue for selcting 316 or 316L. Considering that for some welding for sure the carbon content is important, But whether it is here. The material is used for shaft and impeller.
Thank you again for your kind attention and appreciate your instructions.

Best Regards,
Hooman

Hooman Tehrani
Senior Specialist - Calgary, Alberta, Canada
2007

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First of two simultaneous responses -- 2007

Hooman,

If your concern and question is only about the shaft and impeller of your pump, the influence of the low carbon in this application is nil.
On the other hand, you can improve the corrosion resistance of your pump parts by having them electropolished and passivated.

Kind regards,

Marc Quaghebeur
- Brugge, Belgium

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Second of two simultaneous responses --

The difference is only the Carbon content, which only has a bearing on welding characteristics; 316L will have <0.03%C; 316 will have <0.08%C; less is better, causing fewer problems during welding. They both will perform equally well in terms of corrosion resistance, whether in Chloride or Chloride free environments, certainly better than the 304 grade. Whether your expected Chloride level will actually cause a problem by pitting or Stress Corrosion Cracking is more difficult to determine, and would depend on any of several factors, including the presence of crevices, the operating temperature (50 Centigrade is usually the lower limit for SCC), the level of dissolved Oxygen (the stainlesses rely on Oxygen to provide the necessary Chromium Oxide film for normal corrosion protection)
Regards

Martin Rich
Ship Repair - Plymouth, UK
2007