COMMON PITFALLS DURING SSC AND PITTING TESTING OF SUPERMARTENSITIC STAINLESS STEELS FOR USE IN PIPELINES

摘要

The hardness values of weldments of supermartensitic stainless steels will exceed generallyacceptable limits for “sour service” and qualification testing with simulation of the actual conditionshas to be done. Use of international guidelines, e.g. the EFC-17 document, has shown that there is aneed to specify more details for the testing. The high temperature oxidation during welding willweaken the pitting resistance for SMSS exposed to slightly sour environment. This will influence theinitiation of pitting corrosion and thus the resistance to SSC. The buffer strength in a simulatedenvironment may influence the results and should thus be selected to avoid artificial effects only seenin the laboratory. pH adjustment of a simulated buffer must be done with the test gas in the system. Itis important to check that there has not been any significant change in the pH during testing. In highpressure testing, the pH should be checked prior to testing and after the testing with 1 bar CO_2. Whenstressing 4PB specimens with the root intact, the global deflection to be used must be checked andcalibrated against strain gauge measurements in the HAZ prior to the corrosion testing. In case ofsignificant low temperature creep, a 4PB specimen will experience stress relaxation. If testing of anintact root surface is required, no standard test methodology is available if this relaxation should beavoided.