海底管道疲劳裂纹扩展寿命预报的影响因素分析

Influence factor analysis for fatigue crack propagation life prediction of subsea pipelines

海底管道所处载荷环境复杂,疲劳破坏是主要失效形式之一。由于制造及环境因素,海底管道不可避免会出现裂纹缺陷,对于服役中的海底管道,预报其剩余疲劳寿命并对影响预报结果的因素进行研究具有实践意义。在保守估计法的前提下,采用MTS准则对海底管道裂纹扩展模式进行分析。利用有限元法及1/4节点位移法求解裂纹应力强度因子,随后基于Paris公式的da法对海底管道进行疲劳扩展寿命预报,最后对数值预报结果的影响因素进行探讨。结果表明,当裂纹尺寸增量Δa设置合理时,海底管道裂纹扩展寿命的预报值与试验值相接近,该数值方法能有效预报海底管道的疲劳剩余寿命。裂纹尺寸增量Δa对寿命预报影响很大,从预报精度和计算耗时两方面综合考虑给出了合理选择裂纹尺寸增量Δa的方法。形状比对管道疲劳扩展寿命的影响与初始裂纹尺寸有关。当裂纹尺寸扩展到一定值后继续增加,疲劳扩展寿命变化率并不大。所得结论为服役管道的安全性评估提供参考。

Fatigue is one of the main failure modes due to the complex loading environment of submarine pipelines. Due to manufacturing or environmental factors, crack defects are inevitable in submarine pipelines. For submarine pipelines in service, it is more practical to predict the residual fatigue life and study influence factor of prediction results. On the premise of the Conservative Estimation Method, the MTS criterion is used to analyze the crack propagation mode of submarine pipelines. Solving crack stress intensity factor by FEM combined with 1/4 node displacement method, and then the fatigue life of submarine pipelines is predicted by da method based on Paris formula. Finally, the influence factors of numerical prediction results are discussed. The results show that when the crack size increment Δa is set reasonably, the predicted value of crack propagation life of submarine pipeline is close to the experimental value, and this numerical method can effectively predict the fatigue residual life of submarine pipelines. The choice of the crack size increment has a large impact on the life prediction, and the method of reasonable selection of the crack size increment is given in terms of both prediction accuracy and calculation time consumption. The effect of crack shape ratio on fatigue life is related to the initial crack size. When the crack size expansion continues to increase after a certain value, the fatigue propagation life change rate is slower. The results obtained provide a reference for the safety assessment of pipelines in service.