CNG储气瓶开裂失效分析

Cracking Failure Analysis of a CNG Cylinder

【目的】本文对CNG储气瓶的开裂故障进行了失效分析。文章给出了用户在使用CNG储气瓶时避免出现失效情况的一些建议。另外,对CNG储气瓶厚度进行的超声波测试和水压试验数据,可以用于以后的CNG储气瓶失效数值分析。【方法】用试验调查的方法来确定裂纹产生和气瓶开裂的原因;采用液体渗透的方法来检查CNG储气瓶壳体上的表面破损缺陷和裂纹的位置;采用视觉检查来确定壳体内表面的状况,采用光学显微镜检查裂纹,电子显微镜在适当的放大倍数下,能够检查并描述裂纹表面的精细微观结构,裂纹表面的细微结构显示了断裂起始点的缺陷。最后用光谱分析仪确定了材料的化学成分。另外,还进行了力学性能测试。【结果】CNG储气瓶在水压试验期间发生故障,在低于试验压力的情况下,CNG储气瓶壳体上显示有两条裂纹,并出现了试验液体泄漏的现象。【结论】根据所进行的测试结果,得到结论:压力容器底部的过度腐蚀导致凹坑的形成,成为泄漏裂纹的起始点。

[Purposes] This paper makes cracking failure analysis of a CNG cylinder.Recommendations for avoidance of such scenario with the rest of the user′s compressor cylinder were given.Besides,the ultrasonic test and hydraulic test data of the thickness of the CNG cylinder can be used for the numerical analysis of the failure CNG cylinder.[Methods] Experimental investigation methods were employed to determine possible causes of crack occurrence and vessel rupture.Liquid penetration inspection was performed to check for other surface-breaking defects on the shell and locations of the cracks.Visual examination revealed the condition of the internal surface of the shell.The crack was examined by an optical microscope.The electron microscope can examine and describe the fine microstructure of the crack surface at an appropriate magnification.The fine structure of the crack surface showed the defects at the starting point of the fracture.Finally,the chemical composition of the material was determined by spectral analyzer.In addition,the mechanical properties were tested.[Findings] Cylinder failed during hydraulic test.Under the condition that the test pressure was lower than the test pressure,two cracks were shown on the CNG cylinder shell,and the leakage of the test liquid occurred.[Conclusions] According to results obtained from performed investigations,it was concluded that excessive corrosion at the bottom part of the cylinder caused pits,which were served as initiation points for leakage cracks.