Evaluation of one-dimensional models to predict chatter in spring-loaded pressure relief valves for gas service

Abstract

Literature models proposed to avoid valve instabilities in safety valves for gas service are evaluated. The phenomena occurring during the opening of the safety valve are described to introduce possible sources of instabilities. Models from the last thirty years are classified based on the hypothesis of the source, creating the classifications balance-based and pressure wave models. The experiments used by their authors to validate the models are evaluated. A sensitivity analysis of five models is conducted based on set pressure, inlet line diameter, ratio of specific heats and moving mass. The model results are also compared to experimental data with different gases and set pressures. In all cases the trends of the balance-based models do not match that of the pressure wave models. Compared to measurements with different set pressures, none of the tested models did both match the trends and predict a reliable inlet line length. Comparing against measurements with varying set pressure, the three percent rule only predicted a reliable inlet line length in 2 out of 5 cases. The predicted increasing trend according to the three percent rule did not match the measured trend of decreasing maximum permissible inlet line length. Based on phenomena like the spindle friction and lubrication not being included as model input parameter, and authors finding non-reproducible measurement setups, it is concluded that the instability of a safety valve is a rather stochastic process without considering additional parameters throughout the lifecycle of the safety valve.