With increasing oil & gas demand and depletion of sweet reserves, oil & gas companies in the regionaleconomies are focusing towards the exploitation of sour resources. This necessitates the use of pipelinesand down-hole tubing made from special steels with significant resistance to hydrogen-induced cracking(HIC). These steels are produced through specific technologies for enhanced chemical composition controland microstructural engineering to incorporate the required strength, weld ability and improved HICresistance. It is well established that the HIC initiates at sites with microstructural heterogeneities whetherdue to presence of gross nonmetallic inclusions or the micro-structural constituents. The presence of centralsegregation further aggravates the conditions particularly when the final pipe sizes require the longitudinalslitting of the coils. Presence of non-metallic inclusions in the steel makes it vulnerable to hydrogen-inducedcracking under wet H2S environment. The mechanism of HIC begins with the generation of hydrogen atomsby corrosion reaction of H2S and Fe in the presence of free water. The hydrogen atoms then diffuse intosteel and accumulate around the inclusions. The higher number of inclusions equates to the more sitesavailable for hydrogen adsorption. Recombination of hydrogen atoms to H2 molecules builds up a heavygas pressure in the interface between matrix and inclusions. Cracking initiates because of the tensile stressfield caused by hydrogen gas pressure and crack propagates in the surrounding steel matrix. Thelongitudinal slitting exposes the internal microstructural abnormalities to the skelp edges which are thenincorporated in the thermally stressed weld zone. While the post-weld heat treatment (PWHT) mostlyhomogenizes the weld zone microstructure, the presence of excessive central line features cannot becompletely removed thereby making this zone more prone to HIC attack
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