Influences of Inner Pressure and Overload on Low Cycle Fatigue Behaviors of Elbow Pipes With Local Wall Thinning

Abstract

Low cycle fatigue tests were conducted using 100A elbow pipe specimens with or without local wall thinning. Local wall thinning of 50% of the nominal pipe wall thickness was machined on the inside of the test elbows to simulate metal loss due to flow-accelerated corrosion. The local wall thinning area was machined at the extrados, which has been reported to be the section most likely to suffer local wall thinning. Low cycle fatigue tests were carried out under displacement control using pipe with local wall thinning at the extrados to investigate the influences of an inner pressure of 0∼12 MPa. To simulate seismic events, low cycle fatigue tests were also carried out on pipe with or without wall thinning to investigate the influences of cyclic overloads. No differences in fatigue life were caused by an inner pressure of 3 MPa. However, degradation of fatigue life was caused as inner pressure increased from 6 MPa to 12 MPa. The fatigue lives of overloaded pipes were similar to those of non-overloaded pipes. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.