The safe transport of sour gas requires steels with enhanced hydrogen induced cracking(HIC)resistance.Centerline segregation bands of high hardness microconstituents and non-metallic inclusions are the heterogeneities usually linked to HIC failures in pipeline steels.Full-scale production heats of a low manganese,niobium microalloyed steel were produced by different steel mills for application in sour gas environments.This new steel concept has been manufactured industrially in order to demonstrate the capability to achieve high strength and fracture toughness at low Pcm and with improved control of the centerline segregation and of the inclusion dispersion.Two different pipes with low manganese level(<0.29wt%)were tested to evaluate the manganese induced effect of sulphur solubility on inclusion dispersion.The new alloy design was able to provide both effective strengthening and exceptional fracture toughness,achieving API 5L X65 and in some cases up to X80.Analysis of the pipe microstructure have been performed and consisted of fine grained ferrite with a small volume fraction of uniformly dispersed inclusions.Most importantly,the microstructure was uniform in both the longitudinal and transverse directions and exhibited exceptional consistency along the thickness.Samples were submitted to mechanical property and HIC tests according to API 5L and NACE standards TM0284-2003 without any sign of cracking.The steel concept was compared with the steel market to API X65 pipe and showed similar performance.The results,so far,confirm that this new alloy design provides the unique opportunity to economically produce a high strength pipe steel grade with improved sour service resistance.