10308 Sour Service Limits of Dual-Certified 316/316L Austenitic Stainless Steel and Weldments

To address the widely held concern that ISO15156/NACE MR0175 limits for sour service cracking resistance of Type 316/316L stainless steel in oil & gas production environments were excessively conservative, a program of laboratory studies was undertaken testing parent materials in compliance with the ballot requirements of this standard. In addition, typical weldments were tested under the same conditions to establish whether there were significant differences in cracking resistance. Whilst the existing parent material limits have been shown to be overly conservative and thus can be relaxed to more aggressive conditions, the data submitted to ballot for changes to the limits were based only upon cases where weldments also passed.

In some more extreme conditions weldments were observed to fail the criteria applied whereas parent materials passed, indicating caution is needed in further extending bounding limits. Recommendations are given for the testing of corrosion-resistant alloys where the intention is to ballot ISO15156 / MR 0175 for limits applicable to all equipment forms (which may be welded), that new data are generated which include assessment of typical weldment performance alongside parent materials to provide confidence that these limits remain within boundary conditions demarking lower resistance of weldments compared with parent material.

Keywords: austenitic stainless steels, corrosion testing, GTA welding, H2S, ISO, Mo additions, nitrogen, sour service, standards, stress corrosion cracking, pipes, welded joints, hardness, yield strength