To investigate the failure mechanism of pipelines subjected to mechanical damage, Charpy impact, crack-tip-opening displacement (CTOD) and fatigue-crack growth tests were carried out for six series of line pipe steels with uniaxial plastic prestrain, εpr. The Charpy absorbed energy and critical CTOD (δc) decreased with increasing |εpr|; ln δc = α εpr + β. The derivative, dδc/dεpr, was dependent on the ductile-to-brittle transition temperature of the steels. In the CTOD tests, the prestrain caused ductile-to-brittle transition for the steels with a higher transition temperature. The effects of the compressive εpr on both the reduction of δc and ductile-to-brittle transition were larger than those of the tensile εpr. The compressive εpr accelerated both the fatigue-crack initiation and growth.

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