Pipeline technology specialist STATS Group has completed its first subsea isolation project in China on a 780-kilometer pipeline crucial for supplying gas to Hong Kong.
STATS Group was contracted by COOEC Subsea Technology to provide a temporary isolation of the Yacheng pipeline in the South China Sea. The pipeline had been damaged by a ship’s anchor and left unpiggable at a location about 280 kilometers from shore and in water depths of 90 meters.
After several detailed engineering studies and comprehensive risk assessments, it was determined the best repair solution was to remove the severely dented section of pipeline and two pipeline end manifolds from the seabed on to a pipelay vessel, while the pipeline remained pressurized at 57 bar.
“Since this pipeline is of crucial importance for the supply of gas to Hong Kong, the shutdown period for the repair work needed to be kept to a minimum. Therefore, the repair had to be done without depressurizing and flooding the entire pipeline,” said, Dale Millward, STATS Group Director of EPRS and Subsea Services.
“To ensure safe recovery of both ends of the pipeline onto the pipelay vessel without depressurizing or allowing water ingress into the pipeline, STATS Tecno Plug and BISEP isolation tools were installed. This enabled only the sections of pipeline that were being recovered from the seabed to be isolated.”
Due to the unpiggable defect on the pipeline it was not possible to pig isolation plugs through the pipeline from the permanent pig launcher. Therefore, STATS proposed deploying their dual seal BISEP isolation plug which is installed at location through a hot tap clamp fitting.
Deployed into the pressurized pipeline downstream of the damaged pipeline, the BISEP provided a fully proved double block and bleed isolation barrier against the pipeline gas pressure. This allowed the pipeline to be depressurized between the rear of the BISEP and the pipeline end manifold, enabling the damaged section of pipeline to then be safely cut and removed.
“The strategic use of the BISEP and Tecno Plug isolation tools ensured that the primary project objectives were successfully achieved,” Millward said. “The pipeline was repaired as safely and quickly as possible, without depressurizing or flooding the entire pipeline and while ensuring that any seawater that may have entered the system was removed before the pipeline resumed operation.”
STATS Group designs, manufactures and installs a range of DNV GL type approved isolation tools used for pressurized isolation, hot tapping and plugging in the global oil and gas sector. Their long established track record includes pressurized isolation and Emergency Pipeline Repair System (EPRS) contracts with international operators and contractors.
Headquarters in Aberdeenshire, U.K., STATS Group is supported on Asian projects from a base in Kuala Lumpur and has engineering, design and storage facilities in Abu Dhabi and Qatar.