油井管用特殊ねじ継手におけるねじ山のせん断破壊予測

抄録

The Jump-out caused by the shear failure of the threads is one of the ductile failure modes of the premium threaded connections for Oil Country Tubular Goods (OCTGs). However, actual testing results of the premium threaded connections with the shear failure of the threads were not agreed with the prediction results by the conventional method. In this study, the novel prediction method for the shear failure of the threads on the premium threaded connections was proposed. In this prediction method, it is assumed that shear failure will be occurred when the equivalent plastic strain of the thread exceeds the ductile crack initiation limit. The equivalent plastic strain of the thread was evaluated by finite element analyses which simulated the actual tensile tests of the premium threaded connections. The ductile crack initiation limit was determined by the 3-point bending tests. As a result, this prediction method made it possible to predict the shear failure of the threads on the premium threaded connections occurred at an actual tensile test more accurately than the conventional prediction method.