内压作用下容器和管道“破前漏”评定准则及应用

Leak-before-Break(LBB) Criterion for Defect Assessment of Pressure Vessels and Piping under Internal Pressure

压力容器和管道"破前漏("LBB)准则是一种既安全又经济的评定方法。文章以弹塑性断裂力学为基础,提出了一种压力容器和管道的"破前漏"缺陷评定准则:若容器表面裂纹韧带的极限失稳压力Pu低于相应穿透裂纹的起裂压力Pc,则容器会泄漏失效;若容器表面裂纹韧带的极限失稳压力Pu等于或大于相应穿透裂纹的起裂压力Pc,则容器会爆破失效。同时,分别建立了轴向表面裂纹和周向表面裂纹韧带的极限失稳压力Pu和穿透裂纹的起裂压力Pc的表达式。进而用此方法分析了一些文献提供的实验数据,结果表明,预测的失效形式与实际情况完全相符。

LBB assessment criterion is a simple, reliable and economical safety assessment technology for pressure vessel and piping. In this paper, a new LBB assessment method is introduced based on elastic plastic fracture mechanics. The new criterion is that the failure mode of pressure vessel and piping, leaking or explosion depends on the relative magnitude between plastic collapse stress on ligament and tearing instability stress on cracks tip, if plastic collapse stress on ligament is not smaller than tearing instability stress on cracks tip, explosion failure will happen, otherwise, leaking failure will happen. The formulas calculating plastic collapse stress on ligament and tearing instability stress on cracks tip is established for piping with longitudinal cracks and circumferential cracks respectively. The failure mode for a few cracked piping reported on literatures is forecasted with this method, and the result is consistent with experimental results. It shows that this method is reliable.