Fatigue failure mechanisms of a pressure relief valve

Pressure relief valves (PRVs) in systems supporting constant vessel pressure are required to operate over a wide range of valve strokes, of set pressures and external impacts such as adjacent components vibration, ambient temperature, etc. At the same time, valve operation should be stable, reliable and precise. The aim of this work is to broaden the current knowledge of the PRV self-excited oscillation mechanism. The methods employed during the study are time history review with further spectrogram post processing of the valve input and output parameters in its opening and closing modes. Furthermore, the experimental investigations include valve tests under external vibration conditions. Additionally, an experimental verified mathematical model has been developed that can explain the nature of the valve self-excited oscillation onset. The model represents a one-dimensional approach to predict valve dynamics enhanced with a three-dimensional simulation of the flow choked through the valve. The experimental investigation demonstrated low-frequency self-excited oscillation in the range of 1-10 Hz (amounting to 0.04-0.4 of the valve spring-mass eigenfrequency) throughout the valves, but a number of the valves showed their failure proneness at high-frequency self-excited oscillations within the range of 100-120 Hz (amounting to 4.0 to 4.8 of the valve spring-mass eigenfrequency). The experiments have shown that the reasons of this kind of damage are low-frequency self-excited oscillation as well as external vibration coupled with acoustic resonance of the vessel with an attached the pipe leading to fleeting reduction of drag force in the valve and to high-frequency valve chatter. To prevent of high-frequency self-excited oscillation, the developed design features allow constant and appropriate value of friction force required for chatter elimination in all operating modes of the valve.