Research and Production of Heavy Pipeline Plate for Submarine Gas Transmission Lines at Shougang Steel

Strong gas demand pushes the development of submarine gas transmission projects. The production of submarine pipelines demands heavy thickness, high strength, lower temperature toughness, and sour service crack resistance. This paper reports on the experience with the production of linepipe up to 31.8mm in wall thickness grade X70 intended for offshore applications in China. The alloy/processing design along with production parameters are introduced. The achieved mechanical properties in both plate and pipe are reported. Even with this X70 strength level and heavy wall thickness the low temperature fracture toughness achieved was excellent. Drop weight tear testing (DWTT) achieved an average of 94% shear at −15 °C. Evaluation of the heavy gauge X70 sour service performance was performed according to specifications of NACE TM 0284 and DNV-OS-F101 in low pH (~3) solution A. The results demonstrated that the production had extremely high resistance to HIC and SSCC failure in the testing.