Detailed dynamics. Challenges associated with PRV stability issues for existing installations are not unique to any particular segment of the chemical process industry. This is an industry wide problem that has received a lot of attention from both OSHA and industry associations such as API, ACC, and AFPM. A consistent definition of what constitutes an Engineering Analysis is currently being proposed by API/ACC/AFPM for inclusion in the upcoming revision to API 520.

Screening. In part I of this paper we established a detailed dynamics methodology for the modeling of PRV stability. We demonstrated that (a) the irrecoverable inlet pressure loss due to friction has essentially no impact on PRV stability (also see [3]), (b) PRV instability is caused by the coupling of PRV disk motion with the pressure wave caused by excessive acoustic pressure drop (1/4 wave) during PRV opening/closing, (c) the instability does not amplify, and (d) liquid systems are the most likely to cause damage to piping and piping components..

How to avoid the singing PRV problem. Excitation of acoustic standing waves in a main process flow line closed side branch, such as the inlet line of a pressure relief valve (PRV), can occur due to vortex shedding generated by increased flow in the main process line. The flow velocity for process lines where pressure relief devices are mounted via a side branch should be limited to where ce is the effective isentropic speed of sound of the main process flow pipe fluid system, u is the maximum allowable fluid flow velocity in the main process line, and d/L is the pressure relief device inlet line diameter to length ratio. This limit can be very restrictive for flashing two phase flow.