RESEARCH ON THE FATIGUE CHARACTER OF ERW PIPE WELDED SEAM AND FATIGUE LIFE ASSESSMENT METHOD

摘要

The fatigue character of electric resistance weld (ERW) seams in API X65 grade line pipe steel at the stress ratio of 0.1 and 0.6 have been investigated. Repeated loading was applied to compact tension specimen, and the fatigue crack propagation rate and threshold of X65 ERW pipe seam are tested using high-frequency fatigue testing machine. Radiographic inspection has shown that the crack caused by the cold welding is the main weld defect in the ERW pipe. Based on the failure assessment diagram (FAD) recommended in theAPI 579-2007 and the Miner's linear cumulative damage model, considering the influence of stress ratio to the fatigue life, the fatigue life assessment method for the ERW pipe containing seam defects is established.