On the Influence of the Fluid Dynamics Over the Valve Line Break Set Point in a Dual Phase Gas Pipeline

Abstract

Shut down valves (SDV) actuated by a reaction against a pressure decay are an approach to face pipeline leakages, full ruptures, amidst several other important operational events. They are ordinarily employed at single phase pipelines throughout the world. Their usage at a dual phase gas pipeline is however subjected to specific scenarios in which their actuators (usually line breaks) are not impacted somehow by the presence of liquids, and other particular effects of fluid dynamics. This paper approaches a study based on dual phase numerical flow simulations, using a commercial flow simulator, performed for a Brazilian pipeline, in which a relevant amount of liquid is always present, as well as one or two pigs. The main focus is on the upper bound of the time derivative of pressure distributed along the developed length, aiming to produce a sensitivity analysis, describing situations in which this variable may falsely and appropriately trigger a SDV closure. As most of other important flow events, the critical moment is when the pig approaches the pipeline tail, when major variations on important variables such as flow, pressure and holdup are experienced. Those effects may be deeply augmented when worst case scenarios are imposed and coupled with pigs’ arrivals/withdrawals, such as a pipeline blockage at it’s head or flow rate relevant increase at the tail. These scenarios are simulated and analysed, and the way pressure may relate to the dimensioning of line brakes, is commented.