Smart isolation devices (SIDs) are commonly used in pressurized subsea pipelines to isolate a specific pipeline section that need to be maintained. The sudden stoppage of the SID may cause large water hammer pressures which may threaten both the pipeline and the SID. This paper proposes a novel simulation method by using a coupled dynamic mesh technique to simulate water hammer pressures in pipelines caused by the sudden stoppage of the moving SID. Verifications were conducted in an indoor pipeline system, the reasonable agreement between the results from the two method validated that the proposed method is effective to simulate the water hammer pressures in pipelines with a moving device.
Subsea pipelines have become an important way to transport gas and oil in ocean field. However, corrosions and cracks which threaten the safety of the pipelines and environment are hard to be avoided throughout the lifecycle. As a result, the subsea pipeline maintenance technology using smart isolation devices (SIDs) has been widely developed in recent years (Aleksandersen & Tveit, 2001; Lie & Muangsuankwan, 2015; B. Zhao, Li, Zhang, & Hu, 2010). The schematic diagram of offshore pipelines maintaining using SIDs can be shown in Fig. 1. The SIDs driven by the flowing water moves in the pipeline with a similar velocity as for the flowing water. They start to decelerate suddenly when they approach the targeted section. They will stop at the desired locations which are on the either side of the leak point. Finally, the packers around two SIDs will expand to seal the gap between the SID and the pipeline internal wall to fully stop the water flow. Once the pair of SIDs are in place, then the pipeline section between two SIDs is then isolated and can be repaired. The sudden deceleration of the SIDs may cause severe pressure surges in the pipeline during the application process. This is a key problem which may lead to potential damage to the SID and pipelines. In addition, the SIDs need to be settled at desired locations inside pipeline, the pressure surge is an important parameter to determine the deceleration process and thus the final stopping position of the SIDs. Therefore, the SID stopping position needs to be predicted accurately. This paper aims to develop a simulation method to simulate the water hammer pressures caused by the moving SID inside subsea pipelines. The results can be used to improve the safety of the pipelines and the positioning accuracy of the SID.
