Development of an API 5L X-70 grade steel for sour gas resistance pipelineapplication

An API 5L X-70 grade steel for large diameter pipeline application with sou r gas resistance was developed by electric are furnace processing, furnace ladle treatment, vacuum degassing, ladle treatment, and continuous casting, followed by three different controlled rolling schedules and air cooling o r accelerated cooling. Mechanical properties equivalent to those of an API 5L X-70 grade steel were achieved in slabs with content ranges from 0.25 to 0.37 wt% C, 1.31 to 1.53 wt% Mn, 0.082 to 0.095 wt% Nb, and 0.008 to 0.015 wt% Ti, The slabs were processed by using a controlled rolled and accelera ted cooling schedule.