基于爆裂失效的腐蚀压力管道剩余强度研究

Research on residual strength of corrosive pressure pipelines based on burst failure

为真实反应海洋结构物腐蚀压力管道的结构完整性及其剩余强度,文章以爆裂失效作为腐蚀压力管道的失效准则,基于扩展有限元法,提出了腐蚀压力管道爆裂失效数值分析模型,用以评估压力管道在外表面腐蚀工况下的爆裂压力。以矩形缺陷形状表征管道的腐蚀程度,对不同的腐蚀工况进行非线性数值分析,根据分析结果可知:腐蚀区域最大等效应力随内压变化的曲线可分为线弹性阶段和塑性屈服阶段,在塑性屈服阶段的终点,当腐蚀区域中心处单元达到材料失效准则时,开始起裂并沿轴向扩展,其所对应的内部压力即为爆裂压力;腐蚀管道的爆裂压力均随缺陷区域深度、轴向长度、环向长度的增长而呈指数形式下降,将爆裂压力有限元值与ASME B31G、RSTRENG 0.85标准预测值对比可知现有标准的保守性及局限性;轴向双缺陷压力管道的爆裂压力随着轴向间距的增大而呈指数形式上升,而后爆裂压力趋近于单缺陷管道的爆裂压力值;环向间距对环向双缺陷压力管道爆裂压力在60°~90°、90°~140°、140°~180°三个阶段呈现出不同的影响程度。

In order to truly reflect the structural integrity and residual strength of corrosive pressure pipelines in offshore structures,the burst failure is taken as the failure criterion of corrosive pressure pipelines.Based on the extended finite element method,a numerical analysis model of burst failure of corrosive pressure pipes is proposed to evaluate burst pressure under external corrosion conditions.According to the analysis results,it can be seen that the curves of the maximum equivalent stress in the corrosion zone with the variation of the internal pressure can be divided into the linear elastic stage and the plastic yield stage,at the end of the plastic yielding stage,the unit at the center of the corroded area reaches the material failure criterion and begins to crack and expand in the axial direction,the corresponding internal pressure is the burst pressure.The burst pressure of the corroded pipe decreases exponentially with the increase of depth of the defect area,length and circumferential length of the pipelines.Comparing the predicted values of the finite element burst pressure with those predicted by the ASME B31 G and RSTRENG 0.85 standards,the existing standards are conservative and limited.The burst pressure of the double axial pressure pipe rises exponentially with the increase of the axial spacing,and then the burst pressure approaches the burst pressure value of the single-defect pipeline;At the three stages of 60°~90°,90°~140°and 140°~180°,the circumferential spacing of the double-defect pressure pipe showed different degrees of influence on burst pressure.