Pitting corrosion on 316L SS problem

[MATEGRITY2009]

We have some problem with external pitting corrosion on 316L SS instrument tubing (it leak during in-service).
Can anyone advise me for How to prevent this problem or How to inspect it during in-service?

Thanks for any help...
Maty

 

[SJones]

The only ALARP way to prevent it in marine environments is to change the material as suggested by ISO 21457.

BP have tried chemical treatment as described in NACE Corrosion 2010, Paper 10305

Shell used UV-resistant thermoplastic sheathing as described in NACE Corrosion 2008, Paper 08254, but this was really for expediency.

Woodside require use of 317L that seems to have worked OK.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[EdStainless]

At NASA on the launch platforms they either coat the the 316 with a high grade epoxy or they replace it with AL-6XN.

You need to look at how the corrodants and moisture are getting to the tubes. Sometimes a good paint job is all that you need, but watch out for the fittings, especially the threads. You should leave them un-coated for maintenance and inspection purposes.

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Plymouth Tube

 

[MATEGRITY2009]

Thanks to SJones & EdStainless. as you recommend, now we are plan to upgrading to 317L.

 

[mrfailure]

Did you confirm through metallurgical evaluation that pitting corrosion was the leak mechanism? Sometimes other mechanisms appear to be pitting; you should confirm if you have not already done so.

Aaron Tanzer

http://www.lehightesting.com

 

[Metalguy]

317L may help, or it may not. You should try to determine the Mo content of the 316L you have now before doing anything--assuming you have straight Cl- pitting.

If the Mo is down near the 2% minimum, make sure to buy 317L with the Mo up near the max., 4%. If your 316L has close to 3% Mo, I'd look for a better stainless.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[EdStainless]

I would doubt that 317 is good enough to help.
If some of this ruing is in protected areas where it doesn't get washed by rain then you will need something better.
Without special heat-lot order 316 will be 2.0% Mo and 317 will be 3.0% Mo.

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Plymouth Tube

 

[1gibson]

Sorry I can't come up with a link, but I remember this being a good read from NASA: "Corrosion Performance of Stainless Steels in a Simulated Launch Environment."