It is a challenge to simulate the surge relief valve behavior accurately and handle the "minor frictional losses" from the pipe fittings in the terminal transient analysis. Some hydraulic engineers model the surge relief valve with the assumption that it will perform as ideal default behavior, and proposed relief set points based on the ideal default behavior may not prevent the maximum surge pressures from exceeding 110% maximum operating pressure (MOP) of terminal piping in real-world operations. Furthermore, aggressive relief settings will limit the mainline's capacity. On the other hand, over-conservative relief settings will cause nuisance pipeline start-up failure and relief shutdown events.
A terminal hydraulic study was performed, which included both steady-state and transient analyses. Steady-state simulation is applied to determine the terminal system design, while transient simulation is used to assess the surge potential in the piping system to prevent the pressure dynamics from exceeding 110% of the maximum allowable operating pressure. A mainline pump trip scenario in the terminal is usually the most severe surge event; therefore, a surge relief system is typically installed at the pump's suction side (the pressure specification break point) to protect the lower pressure rated terminal piping from an over-pressure condition after the pump station trip.
This paper discusses the use of an advanced simulation method to successfully match the real suction surge pressure trends for the worst-case terminal transient scenario: the mainline pump station trip accompanied by a surge relief event. The methodology includes arithmetically coding dynamic relief set points and applications of equivalent length in the terminal transient study.
