Study On Fatigue Life Of Submarine Pipelines

Fatigue damage is one of the main failure modes of submarine pipeline. Based onBS7910submarine pipelines containing defects are studied for safety assessment in this paper.Estimated the critical crack size of pipeline at a certain load level and the initial defect failure.The development of the pipe crack is divided into crack initiation and crack propagationphases. Analyses crack initiation life by using local stress-strain approach and, respectively,analyses crack propagation life by using cycle by cycle of crack propagation theory onfracture mechanics. The contents completed in this paper are as follows:(1) The simulation of irregular waves. The stress history of the submarine pipeline inrandom sea conditions is obtained by simulating irregular waves using calculating software.(2)The tube cross-computing model. Of the tube cross-model uses different constraints and spanwere calculated in the same wave under load analysis of pipe stress experience and the stressdistribution across different parts of the.(3) The failure assessment of pipeline defects.Calculate the stress intensity factor and the reference stress of defects using British standardBS7910Level2A engineering fracture assessment method and assess the critical dimension ofdefects on a certain load condition using failure assessment diagram.(4) The crack initiationlife calculation. The development of pipe crack is divided into initiation stage and propagationstage. The initiation life is calculated using local stress-strain approach. And considering loadsequence effects to get the crack propagation life of different points.(5) The crackpropagation life calculation. The stress intensity factor amplitude of pipeline defects iscalculated after crack propagation under load every time. The amplitude is carried into thecrack growth rate model and then the amount of crack propagation is calculated, and then newstress intensity factor is calculated by using extended crack size. The crack propagation life ofpipeline is calculated by Iterative calculation.