Abstract
Corrosion pitting was found under insulation on type 304 austenitic stainless steel pipes used in an ethylene plant since 1980 to transport hydrocarbon products at – 170 ° C. Preliminary investigations established that the corrosion was confined to areas adjacent to the circumferential weld seams. Chlorides were present on the external surface of the pipes owing to ingress through defective insulation. Detailed examination of specimens from the affected pipes revealed that stress corrosion cracks had initiated in the corroded areas near the welds where defects and high residual stresses can be encountered. The cracks had initiated intergranularly before changing to a transgranular mode of crack propagation, typical of stress corrosion cracking of austenitic stainless steels in chloride environments. The evidence suggests that the cracks developed while the plant was not operating when the pipework would have been at ambient temperature.
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