管线钢的裂纹生长预测新模型

氢脆是影响管线钢寿命最严重的破坏机理之一。传统的裂纹生长预测模型没有考虑pH值和温度等环境因素的影响，且只能考虑应力强度较大的加载循环对裂纹生长的影响，忽视了小周期加载的作用。笔者基于氢促进解离（HEDE）和氢增强局部塑性（HELP）两种主流理论，采用氢扩散的动力学模型，建立了一种新的裂纹生长预测模型，并将该模型应用于裂纹生长的预测及小周期对裂纹生长的影响的量化。研究结果表明，建立的裂纹生长模型综合考虑了氢势能、扩散系数、裂纹尖端附近的静水应力和临界加载频率等因素对管线钢裂纹扩展速率的影响，预测值与实验值吻合。利用模型可以将微观裂纹分为惰性、激活、快速增长3个状态，便于管道维护和安全评测；模型将环境因素引入管线钢寿命预测，增强了预测的普适性和准确性；并量化了油气输送中普遍存在的小周期加载对管道裂纹扩展速率的影响。

A new model to predict crack growth rate in pipeline steel

Hydrogen embrittlement is one of the most serious failure mechanisms affecting the life of pipeline steel. The traditional crack growth prediction model does not consider the influences from environmental factors such as pH and temperature, and only those from the loading cycle with large stress on crack growth, ignoring the effect from minor cycles of loading. Based on the two mainstream theories of hydrogen promoted dissociation (HEDE)and hydrogen enhanced local plasticity (HELP), a new crack growth prediction model is created using the kinetic model of hydrogen diffusion, which is applied to the prediction of crack growth and the quantification of the effects from minor cycles of loading on crack growth. The results show that the crack growth model comprehensively considers the effects from hydrogen potential energy, diffusion coefficient, hydrostatic stress near the crack tip and critical loading frequency on the crack growth rate of pipeline steel. The predicted values are consistent with the experimental values. The model can be used to divide the micro-crack into three states:inert, active and rapid growth, which is convenient for pipeline maintenance and safety evaluation. The model introduces environmental factors into pipeline steel life prediction, enhances the universality and accuracy of prediction, and quantifies the effects from minor cycles of loading commonly occurring in oil and gas transport on the crack growth rate of the pipe.