Abstract:

In order to determine the impacts of residual stress relaxation and autofrettage pressure on the in-service pressure vessel safety, the relaxation rule of the residual stress was showed by the test results. The equivalent stress distributed along the vessel wall was calculated under the coupling conditions of the operating pressure and residual stress; the safety coefficient was simulated under the different operating pressures and autofrettage pressures, then the optimum autofrettage pressure was deduced. In this case, a high-pressure polyethylene reaction tube was serviced for 10 years. The results show that the vessel tangential stress in the near wall region decayes from -600MPa to -333MPa fast with the attenuation rate reaching 45%. Attenuation was measured in the elastic region and the residual stress peak location was relocated but a little change in its peak value. For the auto-frettaged pressure vessel under the coupling conditions of operating stress and residual stress, with the residual stress relaxation, the equivalent stress of inner wall surface is increased and the largest equivalent stress is at the junction of the elastic and plastic body, where the safety factor should be calculated. According to this case polyethylene pipe size, the operating pressure is at 180MPa, 280MPa, 380MPa respectively, then the best autofrettage treatment pressure is at 606MPa, 677MPa, 743MPa respectively, the safety factor is larger 16%, 26%, 37% respectively than residual stress all attenuation to 0. With the higher operating pressure, the vessel safety factor increased by optimal autofrettage process is higher, but impact caused by the residual stress attenuation is greater.

Key words:  residual stress relaxation, optimal autofrettage pressure, safety factor, pressure vessel, polyethylene reaction tube

摘要：

为了确定残余应力松弛和自增强处理压力对在役高压容器安全性能的影响，通过分析测试结果获得了残余应力的松弛规律，计算了在工作压力、残余应力作用下的当量等效应力沿壁厚分布情况，模拟计算出了不同的工作压力、自增强处理压力下的安全系数，推导出了最佳自增强处理压力。结果表明所研究的高压聚乙烯反应管在使用10年后，环向应力在近内壁区衰减最快，从-600MPa衰减到-333MPa，衰减率达45%；在弹性区衰减较小，残余应力峰值位置外移，但其峰值大小变化不大。对于自增强处理后的压力容器，在工作压力作用下，随着残余应力的松弛，内壁面当量等效应力增大，当量等效应力在弹塑性交界处最大，应该按此处的当量等效应力计算安全系数。依据示例聚乙烯反应管尺寸，模拟计算出在工作压力分别为180、280、380MPa时，经过自增强处理压力分别为606、677、743MPa的最佳自增强处理后，其安全系数比残余应力全部衰减为0时分别高16%、26%、37%。压力容器工作压力越大，经最佳自增强处理后安全系数增大得越多，但残余应力衰减对其安全影响越大。

关键词: 残余应力松弛, 最佳自增强处理压力, 安全系数, 高压容器, 聚乙烯反应管