EXPERIMENTAL AND NUMERIC ANALYSIS OF SPRING-LOADED PRESSURE RELIEF VALE

The majority of oil and refined-product pipelines in Brazil have their protection systems design based on pressure relief valves. Thus, the proper design and operation of these valves is essential to ensure the safety of pipelines and loading/unloading terminals during any abnormal operation conditions that generate overpressures. These valves work by relieving the internal pressure in case it exceeds a set value. In simple terms, the spring-type pressure relief valve has a disk which is pressed by a spring against the inlet nozzle of the valve. When the pressure rises, the force generated on the surface of the disc increases and, depending on the pressure relief valve set point, the force due to pressure overcomes the force exerted by the spring, causing the disk to rise and discharge the fluid through the outlet nozzle to the relief line, reducing the pressure level within the pipeline. Using this principle, the relief valve ensures that the pipeline is not subjected to high transient pressures, which could, otherwise, lead to pipeline or equipment rupture and possible product leakage. Despite its importance, the models commercially available to simulate the transient behavior of pressure relief valves do not present a satisfactory performance. The present paper presents an experimental study aimed at determining the dynamic behavior of a commercial spring-type relief valve. The valve was installed in a pipe loop where the flow was established. The valve and the loop were instrumented with pressure and flow transducers. The transient motion of the valve disc was measured with a fast-response displacement transducer. The transient in the flow loop was generated by the controlled closing of a block valve positioned downstream of the relief valve. The recorded transient data for disc position, upstream and downstream pressures, and discharge flow rates were compared with results predicted by different models for relief valve dynamic behavior implemented in a commercial pipeline flow simulation software.