Failure investigation of liquefied petroleum gas cylinder using FAD and XFEM

To assess the reliability and performance of household liquefied petroleum gas (LPG) cylinder is important for safety standard. Such crack-like flaws in material of cylinder might lead to many serious catastrophes like fluid leakage and gas explosion. In this work, the failure assessment diagram (FAD) was determined according to the standard API 579 for inland produced LPG cylinders. A brand-new and used LPG cylinder of the same steel grade were investigated. Metallographic analyses, tensile tests and fracture mechanics tests using a single-edge tension SE(T) specimen were carried out. The direct current potential drop (DCPD) method was applied by the SE(T) test and the critical contour J-Integral for crack initiation was identified. Then, FE simulations of the cylinders afflicted with different crack configurations were performed under varying internal pressures. The corresponding critical pressure loads were determined and the level 3 FAD for a crack onset could be generated. It was found that the mechanical properties of used cylinder were obviously deteriorated that could therefore lead to an earlier failure when an unexpected certain pressure is given. In addition, FE simulations coupled with extended finite element method (XFEM) were conducted in order to describe the crack propagation in both cylinders. The results were firstly verified by comparing the load vs. crack mouth opening displacement (CMOD) curves. It was shown that the crack propagation in the aged LPG cylinder would become considerably stronger when unintended crack is present.