In 2023 an Oil and Gas operator in the East China Sea required upgrading to their 28in Gas Export Pipeline (GEP), including modification of the pig launcher and connecting pipework at one of their offshore production platforms. The 345km long GEP is exporting produced natural gas between the offshore production platforms and onshore processing terminal and is hence one of the most critical pipelines in their network. The work which took place during a 70-day period in 4th quarter of 2023 required temporary stopping of the gas production and depressurizing a section of the GEP and topside piping so that the upgrading work could be done safely. The operator was initially faced with two options to facilitate this work, by either depressurizing the GEP entirely for the duration of the project or provide temporary pressure isolation locally at the platform.

The operator decided on using inline Double Block and Monitor (DBM) pipeline isolation by deploying High-Pressure Isolation Tool (HPIT) provided by T.D. Williamson (TDW), also known as SmartPlug®. One unique thing with this project was that the operator had the opportunity to continue the gas production via a temporary bypass pipeline while continuing the modification work such that days of lost gas production could be kept to a minimum. To facilitate this, two isolations using the same HPIT tool were required in single launch and retrieval. This paper describes the steps taken to plan and execute the isolations from site visit, engineering to successfully executing two isolations during single launch into the GEP.  It also discusses the benefits the HPIT isolation provided to the project and savings to the environment from what otherwise would have been significant CO2 emissions from flaring of a large volume of natural gas to empty the GEP.