Fatigue tests were carried out on ERW line pipes 200 mm and 300 mm in diameter with a severe gouge in dent type defect. Hoop stress fluctuation between 15% and 30% of the yield stress of the pipe materials was applied by cyclic internal pressure loading. By the parameter Q, a function of defect size and fracture toughness, fatigue behavior could have been well explained. Fatigue behavior differed above and below the threshold Q (Qth. When Q<Qth, crack propagation was initially associated with ductile crack growth, and therefore, fatigue life, Nf, decreased to less than 1000 cycles. On the contrary, Nf was larger than 1000 cycles when Q≧Qth. Nf was predictable with a power law equation incorporating dent depth, gouge depth, and stress amplitude when Q≧Qth. A gouge in a dent with Q<Qth, requires immediate repair or replacement.

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