NACE and chloride limits for austenitic SS.

[enmax]

This is a specific question about NACE MR0175/ISO 15156-3:2003 which concerns the use of corrosion resistant alloys in oil and gas production. Table A.2 of that standard gives the environmental limits for the use of austenitic stainless steels. A maximum temperature of 60 deg C is given - presumably to avoid stress corrosion cracking - but with regard to chloride concentration limits it says "Any combination of chloride concentration and in situ pH occurring in production environments are acceptable". Can this be correct? My understanding is that more than a few hundred ppm chloride (even at room temperature, never mind 60 deg C) would cause severe pitting in 304L and 316L. The limits for crevice corroion would be even lower. Any explanation would be appreciated.

 

[SJones]

The explanation is given in the 'Warning' paragraph at the very start and in the third paragraph under '1 Scope'. In summary, ISO 15156 deals only with cracking; general and localised corrosion are not addressed.

Steve Jones
Materials & Corrosion Engineer

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

 

[EdStainless]

Thanks SJ, The point is in the title of the standard, it only addresses cracking. other forms of corrosion are your problem to take care of in a responsible engineering method.
Yes at pH=4, 100ppm Cl, and no oxygen, 316 will pit at 30C, but that is another issue.

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Plymouth Tube

 

[enmax]

Thanks Ed and Steve - I'm always telling my kids to read instructions - I should practice what I preach.

Regards

 

[blacksmith37]

Yes the NACE MR 01-75 ( ISO 15156 ) addresses only hydrogen sulfide stress corrosion cracking (also called hydrogen stress cracking ,and a dozen other names).
Don't feel bad; at least half of the inquiries that came to the T1 F1 (MR 01-75 committee) -years ago when I was on it- were regarding Chloride SCC of austenitics or general corrosion. There were endless discussions of how much "helpful" advice for these other conditions, should be in the document