NACE MR-01-75 Question

[lukerobert]

NACE MR-01-75 says that maximum allowable NI content for alloy steels in sour service is to be less than 1%. Is there a restriction on weld metal composition with regard to NI content under the same scenario? Is this also set at a max of 1%?

 

[pradipgoswami]

Hi Luke,

ANSI/NACE MR0175/ISO 15156-2:2009, Clause A.2.1.4 allows the following:- Welding consumables and procedures that produce a deposit containing more than 1 % mass fraction nickel are acceptable provided successful weld SSC qualification by testing in accordance with Annex B(of MR 0175/ISO 15156) is met.

However the default rule is also 1% Max Nickel in the weld metal, as described in many welding consumable manufacturer's consumable specification sheet.

Apparently few years ago TWI intiated the following Group Sponsored Project(see the atatchment), titled as : "Raising the Acceptance Level for Nickel in C-Mn Welds for Sour Service". If the other members could shed some lights on this subject it would be very well appreciated.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[wegm]

You may have a look at this link:

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=5&t=244

 

[blacksmith37]

In the 70's and after, there were a few failures of 43XX alloys (and weldments) in H2S. Some failures could be attributed to Ni/Mn segregation causing a lowered critical temp. some were caused by imperfect HT temps or only a single temper cycle . A variety of testing was sponsored by Inco and then NiDi (Dr Bruce Craig ). The data could never convince the MR 01-75 committee that Ni was safe.
Note, OCTG grades T95, C105,C110, (sour service) use very low limits on Ni and Mn and use very high tempering temps like 1400F.

 

[redpicker]

I can support blacksmith37's comments. From personal experience, the presence of 0.25% Ni in an otherwise identical chemistries will cause Low Alloy steels designed for H2S resistance to fail 85% SMYS Method A testing at the 110 KSI strength levels. And, Mn level in these steels is kept below 0.35 or so. I can't explain exactly why (although the segregation issues mentioned are probably involved), but the effect is certainly there. I say the segregation issues are "probably" involved because I never directly observed banding or other evidence of macro-segregation in these steels, but the high Ni residual heats had to be diverted to either lower yield sour service grades or, more commonly, to non-Sour grades.

Interestingly, Ni at these levels also has a surprisingly negative effect on low temperature impact strength values. The segregation idea may be contributing to both.

rp