In order to stabilize the supply of gas to its domestic market, China Petroleum Corporation (CPC), Taiwan, the sole natural gas supplier, has established an integrated gas distribution network in the western part of Taiwan with an inland transmission trunk line, offshore transmission trunk line and regional transmission loops. CPC's gas pipeline planning is based on the concept of forming a ring-shaped gas transmission network along the island. The 36-inch diameter Yung-An to Tung-Hsiao offshore pipeline (Figure 1) is the largest and longest transmission pipeline in the entire network, delivering gas from southern Taiwan to northern Taiwan, where the dominant gas market is located. It was discovered that the emergency shutdown valves (ESDV) at both the Yung-An LNG terminal and the Tung-Hsiao gas transfer station, which are connected by a 237.7-km (147.7-mi), 36-inch offshore pipeline, required replacement or maintenance so that
CPC could resume operational pigging of the pipeline and carry out regular in-line inspection (ILI), as required by regulations.
Methods, Procedures, Process: For this project, CPC decided to apply advanced isolation technology known as SmartPlug® in-line isolation and hot tapping and STOPPLE® isolation technology to isolate the pipeline pressure at 60 bar (870 psi) before executing the repair work. The isolation enabled the operator to avoid depressurizing and purging their entire 237.7-km (147.7-mile) gas export pipeline while mitigating safety concerns associated with defective ESDVs and corroded components. This paper describes the steps taken from planning, to site visit and engineering, to safely and successfully executing the isolation.
Novel/Additive Information: Continued operation with defective pipeline isolation valves and corroded components would have been highly undesirable and would have caused many safety concerns for the pipeline's owner. Using SmartPlug with hot tapping and STOPPLE technology allowed the operator to avoid depressurizing and purging the entire gas export line, which would have meant flaring venting a large quantity of natural gas, a huge business opportunity loss and an event of significant environmental impact. It would have taken several days to fully depressurize and flare the entire pipeline, and several more days to reintroduce hydrocarbons into the pipeline before gas deliveries could resume. The project schedule allowed for only seven days of work during the 2019 Chinese New Year holidays, when energy consumption in Taiwan is lower than usual. While the 36-inch pipeline was isolated, CPC also took the opportunity to replace some leaking valves at both the launching and receiving ends of the pipeline.