Large diameter TMCP (Thermo-Mechanically Controlled Process) pipelines have recently shown detrimental local variations in mechanical properties. Additionally, industry experience demonstrated that API(1) 5L / ISO(2) 3183 and NACE MR 0175 / ISO 15156 compliant TMCP linepipe presented increased ID surface hardness, commonly known as hardspots or hard layers. These surface anomalies are difficult to detect as standard QA/QC included in API/ISO standards do not cover this matter sufficiently. In cases where hard spots are present (e.g. as it has been observed on API 5L X60, X65 grades) this may lead to rapid SSC failures in severe sour service environments. Thus, the European Pipeline Research Group (EPRG)(3) launched at the end of 2017 a research program to define the SSC (Sulfide Stress Cracking) limits of TMCP pipes, to do a literature survey on Non-Destructive Techniques (NDT) able to detect surface hardness anomalies, and finally to reproduce hard layers through a “lab scale TMCP rolling” and point out the potential root cause of surface hardening. The current paper highlights work in progress with a specific focus on SSC limits of both API 5L X52 and X65 grades suitable for sour service and for natural gas applications in compliance with NACE MR0175/ISO 15156 - SSC Region 3 requirements. Threshold stress is determined using NACE TM0316 four-point bend testing in environments ranging from 1 to 17 bar of partial pressure of H2S. Results are discussed with respect to the through wall hardness of materials and recommendations are then proposed to be considered in general for sour service line pipe projects.
Key words: sulfide stress cracking, SSC, hydrogen induced cracking, HIC, blistering, ThermoMechanically Controlled Process, TMCP, linepipe, hardness