RISER RELIEF VALVE DYNAMIC INTERACTIONS (EXTENSION TO A PREVIOUS MODEL)

Further investigation of the dynamic stability behavior of a typical p ilot-operated relief valve is reported. The present study is an extens ion to Botros et al. (1997) model, which includes mapping of the oscil lating frequencies and amplitudes with riser dimensionless length L/D; inclusion of the effects of a wedge-O-ring seal in the model; detaile d analyses of the field tests revealing unknown values for model param eters. These model refinements resulted in a better agreement between simulation results and field measurements, Analysis of piston oscillat ion frequencies and amplitudes indicates that the piston oscillation f requency mirrors the riser's one-quarter-wave resonance frequency for lower values of L/D. At L/D = 20 and higher, two modes of oscillations started to emerge with two distinct frequencies. Maximum oscillation amplitudes occurred at L/D corresponding to one-quarter wave. Wedge-O- ring seal mechanism helps in suppressing piston oscillations; bur it m ust be used in conjunction with a proper lubricant, otherwise the pist on may jam partway during the upward stroke.