Subsea Pipeline Isolation and Repair of Anchor Damage on 28” Gas Export Line

STATS Group were contracted by COOEC Subsea Technology Co.,Ltd. to provide temporary subsea isolation of the YaCheng pipeline, situated in the South China Sea. The 780km 28” subsea gas export pipeline supplies gas to Hong Kong and had become damaged by an anchor approximately 280km from Hong Kong, at a water depth of 90 meters. The dragged anchor damaged one of two subsea Pipeline End Manifolds (PLEM) and made a severe dent in the pipeline adjacent to the downstream PLEM. When the damage was identified, a temporary repair was implemented by installing a 400m 14” bypass between the PLEMs, which enabled the pipeline to continue operating at its normal operating pressure of 70bar, while the permanent repair was being engineered.
As the pipeline is of crucial importance for the supply of gas to Hong Kong, the shut-down period for the repair needed to be kept as short as possible, therefore the repair had to be done without depressurising and flooding the entire pipeline.
To enable safe recovery of both ends of the subsea pipeline onto the pipelay vessel, without depressurising the entire pipeline or allowing water ingress into the pipeline, STATS Tecno Plug and BISEP’s were installed into the pipeline to isolate only the sections of pipeline being recovered to the surface.
To ensure diver and worksite safety, the Tecno Plug and BISEP had to provide; fully proved, fail-safe, Double Block and Bleed (DBB) isolation barriers from the pressurised pipelines, in compliance with industry guidance on Isolation and Intervention for Diver Access to Subsea Systems.
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