![]() at inorganic inclusions (manganese sulfur) – and allowed to recollect with other trapped atomic hydrogen, this leads to the formation of molecular hydrogen and local buildup of pressure, which results in mid-wall blisters and cracking parallel to the wall. When atomic hydrogen is trapped at irregularities within the pipe steel – e.g. Following aqueous corrosion reactions in the presence of H2S on the pipe internal surface, atomic hydrogen is produced and absorbed in the pipe steel. The most common conditions for these are sour environments. Sour Cracking - HIC, Sulfide Stress Corrosion Cracking (SSCC)Įnvironmentally assisted cracking can also occur internally in pipelines. It is nevertheless accepted that some level of stress cycling is required for initiation and growth. Some investigations have also associated anaerobic microbial activity with the initiation of near-neutral pH SCC overall, however, the mechanism remains unclear and debated. It is thought to be most prevalent in high latitudes where there is a marked seasonal change in the carbon dioxide content of the soil. The cracks tend to be wider, with corroded crack walls and filled with corrosion products. In contrast to high pH SCC, the crack propagation through pipe wall thickness is of a transgranular nature. Near-neutral pH SCC cracking typically occurs in association with pits and general corrosion, as it occurs under freely corroding conditions, i.e. As for high pH SCC, the surface cracks generally form colonies in the axial direction of the pipe. Near-neutral pH SCC also occurs on external pipe surfaces under areas of coating disbondment but where CP is fully shielded. Near Neutral pH Stress Corrosion Cracking ![]()
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