STATS Group has completed its first subsea isolation project in China on a 780km pipeline which is crucial for supplying gas to Hong Kong.
STATS 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 280km from shore and in water depths of 90 metres.
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 pressurised at 57 bar.
STATS Group, Dale Millward, Director of EPRS and Subsea Services, said: “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 depressurising and flooding the entire pipeline.
“To ensure safe recovery of both ends of the pipeline onto the pipelay vessel without depressurising 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 pressurised 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 depressurised between the rear of the BISEP and the pipeline end manifold, enabling the damaged section of pipeline to then be safely cut and removed.
Dale Millward said: “The strategic use of the BISEP and Tecno Plug isolation tools ensured that the primary project objectives were successfully achieved. The pipeline was repaired as safely and quickly as possible, without depressurising or flooding the entire pipeline and while ensuring that any seawater that may have entered the system was removed before the pipeline resumed operation.”