Fatigue Behavior of Line Pipes Subjected to Severe Mechanical Damage

Fatigue behavior of electrically resistance welded (ERW) line pipes with a gouge in a dent was experimentally investigated. After denting and machining a gouge, fluctuating internal pressure was applied to line pipes. The fatigue behavior differed above and below the threshold Q([Q.sub.th]), as a function of defect size and fracture toughness. When Q [is less than] [Q.sub.th], ductile crack growth was observed with a consequent decrease in fatigue life. On the contrary, fatigue crack growth was observed when Q [is greater than or equal to] [Q.sub.th]. Fatigue life was predictable with an experimentally based power law equation incorporating dent depth, gouge depth, and hoop stress amplitude when Q [is greater than or equal to] [Q.sub.th].