Boundaries Definition for Modeling Transients in Oil Terminals

Terminals are an integral part of transmission pipelines that can operate in different modes. The two most common modes are single injection and single delivery. Because pressure waves generated after accidental valve closures, pump trips, or others can travel many miles in a few seconds, it is a current practice to simulate the whole mainline to the next pump station, upstream or downstream, due to the lack of a standard method to identify boundaries. This paper proposes a method to define the minimum modeling boundary. This boundary is especially useful when the available data is limited, when multiple suppliers / pipeline owners are connected to a terminal, when advanced simulation software or powerful computers are not available, or when the goal is to avoid unnecessary, complex labor-intensive simulations. The technique consists of identifying a boundary located far enough in the mainline so that pressure waves do not interfere with the development of pressure surges after transient events in the facility piping or in a segment of a pipeline that has the weakest pipe. This straightforward method is supported by concepts published by well-known authorities in the transient hydraulics field and tested with available pipeline simulation software. After reading this paper, the reader will be able to answer these questions: • How much data do I need? • How many permutations? • What info is critical for this method? • Where is the boundary? • What causes a wrong selection? In summary, the hydraulic engineer will be able to shorten the current boundary to small fractions: up to 1/25 in the case of injection facilities and up to 2/25 in the case of delivery facilities. As well, readers will confirm that the hydraulic conditions in the mainlines beyond these boundaries don’t have any effect on the facilities’ piping due to transient events such as accidental valve closures or pumps trips, the most common initiators of large pressure surges.