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. 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. This allowed the company to avoid having to remove the contents of the entire 237.7-km (147.7-mile) gas line, which would have significantly extended the shutdown period.

The chosen isolation method helped CPC secure the “fastest and most efficient” method to resume gas supply to northern Taiwan and increased confidence in the use of this method for inline pipeline inspection in the future. The project only allowed seven days for the work during the 2019 Chinese New Year holidays, when energy consumption in Taiwan is lower than usual. The company also conducted an in-depth risk study and several workshops to assure the risk management of this project before execution. While the 36-inch pipeline was isolated, CPC also took the opportunity to replace other leaking valves at the launching and receiving ends of the pipeline.

The isolation enabled the operator to avoid depressurizing and purging their entire 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.

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