Effect of Steam Hammer Pressure Wave Steepening on Pipe Supports

Abstract

Safety valve closure is employed within power plant piping systems to protect sensitive components from damage due to irregular events causing abrupt pressure variations of the thermal fluid flow. The valve closure creates a sudden obstruction to the flow, generating a pressure wave within the fluid which travels upstream and impacts at the pipe elbows. Such an event is known as steam hammer. This steam hammer pressure wave is capable of producing significant loads and stresses which can disrupt the piping supports as the wave travels throughout the pipe system. Previous studies have shown that the magnitude of these transient loads depend upon the characteristics of the flow, valve closure time, elbow-to-elbow pipe section lengths, the piping system flexibility, and the ‘steepness’ of the pressure transient. The latter effect has been ignored in most steam hammer studies; however, wave steepening has been shown to have a significant effect in cases where the pressure wave travels long distances from the safety valve. This study focuses on Computational Fluid Dynamics (CFD) modeling of rapid valve closure to produce this wave steepening effect and to investigate the significance in terms of transient pipe support loads.