X80 grade high strength large diameter line pipe (UOE Pipe) for sour service has been studied. Increasing Mn content to provide strength of X80 increases HIC susceptibility due to center segregation of Mn in continuously cast slabs. The Mn content should be controlled less
than 1.4% to maintain HIC resistance in the NACE TM0177 solution. The required strength can be obtained by addition of 0.5% Cr and accelerated controlled cooling after rolling. It has been clarified that Cr is very useful in providing high strength over X70 without accelerating the center segregation of Mn. SSC resistance can be improved by controlling maximum hardness of weld metal lower than 230Hv. Sour service X80 UOE pipes of two sizes were manufactured on large scales based on these experimental results. These pipes showed good low temperature toughness and HIC resistance in the NACE TM0177 solution.
Keywords: HIC, SSC, X80, large diameter line pipe, segregation, low Cr, accelerated controlled cooling, Weld