Reliability Calculation of Fatigue Damage and Fatigue Life of Submarine Pipeline

The long-term sea state for submarine pipeline within its service period is regarded as several short-term sea states.The short-term distribution of each sea state obeys the Rayleigh distribution.The stress response spectrum of submarine pipeline in each sea state is determined by modal analysis and spectrum analysis.Utilizing Miner linear cumulative damage theory,the fatigue damage of submarine pipeline under wave loads is investigated.The reliability analysis of fatigue life is carried out in combination with S-N curve.The related parameters affecting fatigue damage and reliability are also investigated.Fatigue life is a complicat-ed stochastic process.The mathematical expression of fatigue life and the limit state equation of fatigue failure are obtained by integrating the four factors in uncertainty of fatigue strength,randomicity of fatigue load,uncertain errors of calculated stress range and actual stress range as well as approximation of Miner linear cumulative damage theory.Taking the submarine pipeline in Chengdao Oilfield as an example,the effects of pipeline boundaries,span length and hydrodynamic parameters on fatigue damage and reliability are analyzed.Among them,the influence of span length on the fatigue damage and reliability is the strongest,the inertia force coefficient is the stronger and the drag force coefficient can be neglected.