Investigation the causes of failure of LPG Tanks relife valves

The relife valve is a critical part of a device that has great importance to ensure security of related persons life and financial. Use this piece is necessary in the system with possibility of increasing the internal pressure of the system. One of these systems is gas tanks that is such as a mobile bomb and in case of malfunctioning of relife valve, in which place there is a possibility of explosion. In this study, evaluation of valve failure a portable LPG gas cylinder is performed. For this purpose, chemical analysis, metallography, mechanical properties, and in particular the fractography was done on The broken sample. The surface quality of the samples were examined by stereomicroscope and scanning electron microscopy. The results show the fatigue failure. in effect of loss of surface quality due to pitting of the of inappropriate machining. The main factors contributing to this phenomenon was detected reduction of surface quality due to pitting and improper machining.