REVIEW AND CRITICAL ASSESSMENT OF HARDNESS CRITERION TO AVOID SULFIDE STRESS CRACKING IN PIPELINE WELDS

Although employing high strength steels in pipelines provides many benefits, it is difficult to satisfy all required mechanical properties simultaneously because some are potentially at odds with each other. Additionally, when new natural gas pipelines are constructed for severe sour service, the hardness must be below 248 Vickers to avoid sulfide stress cracking (SSC) regardless of pipe grades, and this has been standardized by NACE and applied for approximately five decades. On the other hand, the relevance of this hardness criterion has been controversial. This paper proposes three possible methods to improve SSC resistance for weld metals; 1) reducing impurities, 2) producing fine and homogeneous microstructure, 3) controlling microstructures that characterize high hydrogen permeability, solubility, and low diffusivity. This paper states that reducing impurities and producing fine and homogeneous microstructure would reduce SSC susceptibility and an acicular ferrite would be the effective microstructure to increase SSC resistance for weld metals.