Corrosion Allowance for Stainless Steel Pipes

[JackLeeKH3]

Hi there,

I have a doubt that I couldn't find some good explanation on it.

In school time, i was thought that SS is good corrosion resistance allowance. Theoretically, it is required zero corrosion allowance. However, when i go through some standard pipe class, I noticed that some companies did included 1.5mm corrosion allowance for SS material (304/304L and 316/316L). Could you advice based on what basis, 1.5mm is added? Who is the party that confirm the requirement of 1.5mm corrosion allowance?

Looking forward your valuable opinion.

Thank you.

 

[BigInch]

Contrary to popular belief, SS is not "stainless". It will corrode in the presence of some elements.

Ask your materials selection consultant for the best material recommendation t suit your purposes.

 

[bimr]

It is stainless free but not corrosion free. Exposure to air is the natural passivation treatment for stainless steel. This exposure produces a thin, durable chromium oxide film that forms rapidly on the alloy surface and gives SS its characteristic stainless quality. Exposure to water or other oxidizing environments also produces this passivating film. This film helps to protect from corrosion, but SS can still corrode.

http://www.eng-tips.com/viewthread.cfm?qid=171512

 

[weldstan]

In most cases austenitic stainless steels corrode locally (pitting. crevice type corrosion) so adding a corrosion allowance is somewhat superfluous - but not always! The Engineers' or Owners' corrosion specialists make the decision regarding CA or it's because "that's the way we always do it!"

 

[LittleInch]

I agree with weldstan - 304 and 316 are relatively light stainless steels - if you need really high resistance you need Duplex or Super Duplex - more Chrome and a different structure.

Normally you would either use Stl stl or not. Adding a CA seems rather strange.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JackLeeKH3]

Thanks all for the valuable opinion.

After read through few more forums, found that corrosion allowance on stainless steel shall be determine based on it service and if there is any expected uniform corrosion rate. It is not economic to add wall thickness to counter pitting issue. I did check with our material selection specialist why we need to add 1.5mm C.A. for duplex. He replied that "it is our standard C.A. for pipes". I was stunned!!!

Weldstan, I agree with you! - "that's the way we always do it!" - This is the typical answer that i got from my colleagues which is the biggest block that i have whenever i would like to know more and know how on something.