Pressure relief valves are essential components of natural gas pipelines. To ensure safe operation of the pipeline it is imperative that these valves function properly and reliably. Improper installation or setup can lead to potentially catastrophic problems in the field. In this study the performance of a commonly used pilot operated safety relief valve was examined under both normal and abnormal circumstances. The fundamental operating principles of the valve are reviewed, followed by presentation of experimental data illustrating the blowdown performance of the valve. The experimental techniques employed in the laboratory to simulate pipeline conditions are also described. While the performance of the relief valve was consistent with the manufacturer's specifications under normal setup and operation, significant problems were found to exist when the pilot was incorrectly adjusted, or when pressure pulsations were present. Examples of both cyclic venting and premature relief are shown in the paper. To assist in determining when a pulsation suppressor is required a semi-emperical relationship between pulsation strength, and premature opening pressure, is proposed.


Safety relief valves are installed on pipelines, typically at the discharge of compressor stations, to make certain that the operating pressure within the line never exceeds the conditions for which the system was designed. These valves are essential to the safe operation of the pipeline and must be properly installed in order to function effectively. Several factors that can affect the performance of relief valves are valve design, valve settings, sense line installation and the presence of pressure pulsations in the system to which they are attached.

Numerous researchers have investigated the performance of both pressure and safety relief valves under a variety of conditions. Several have investigated the effect of flow induced pulsation on direct acting safety relief valve performance from the perspective of eliminating the pulsations. Others have analyzed the stability of valves connected to piping, or vessels. Two papers and deal with pressure pulsation affecting the opening pressure of a relief valve. While the information presented in these papers is helpful in understanding relief valve performance, they do not explore the dynamics of pilot operated relief valves. To our knowledge this is the first time that the dynamics of pilot internals have been discussed in the literature as a cause of premature release.

This paper specifically focuses on the behavior of a typical safety relief valve pilot and its effect on overall valve performance. It will be shown that under normal setup and operation, the pilot behaved consistently with the manufacturer's specifications; however, it will also be shown that significant problems result when the pilot is incorrectly set or when pressure pulsation is present at the inlet of the pilot. We will begin by briefly reviewing the normal operation of the pilot.

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