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Pipeline isolation holds for 70 days

Published by
World Pipelines,

The restrictions placed by rigorous safety and marine preservation regulations in the environmentally sensitive Tokyo Bay region of Japan make operating a subsea crude pipeline challenging. Moreover, it can make the complex task of pipeline repair even more daunting.

When a typhoon damaged the elbow joint of a 24 in. subsea crude pipeline that was located 4 km (2.3 miles) offshore Tokyo Bay in May 2015, the operator acted immediately to mitigate the situation. Alongside clean-up, the operator took the line out of service and made a temporary repair. That, however, was just a stop-gap measure. The next step was to evaluate how to remove and replace the damaged elbow joint and pipeline end manifold (PLEM) whilst aligning with the regulations that were in place.

Since the pipeline connects the loading single buoy mooring to the 40 in. main subsea crude pipeline that supplys an onshore refinery, keeping the system in service during the replacement project while also ensuring zero spillage in the highly environmentally-controlled waters were priorities.

To achieve these goals, the operator contracted T.D. Williamson (TDW) to create a safe subsea work zone using its hot tapping and STOPPLE® isolation system. This was the first subsea application of STOPPLE isolation technology in Japan.

The STOPPLE system provides temporary isolation of the damaged section so that repairs and maintenance can be performed effectively, even under the demanding environmental and safety conditions.

To ensure a safe and efficient isolation operation without additional delays, before deployment, TDW prepared and tested subsea tapping machines and STOPPLE isolation equipment, conducted divers’ training and completed a mock-up to confirm that the STOPPLE machine would be completely compatible with the subsea mechanical clamp.

Any subsea intervention is demanding, however, there were additional challenges in this case. Chiefly, the Coast Guard limited diver access to the work zone to daylight hours and mandated the use of an air diving wand as opposed to the preferred method of saturation diving. This restriction meant that daily set-up and close-out of diving equipment took almost 90 minutes out of a six or seven hour work day. Combined with inclement weather, the Coast Guard’s requirements extended the project to 70 days – approximately three times the duration of a typical hot tapping and plugging operation.

Even still, using the STOPPLE methodology, TDW achieved a successful first-time isolation just 5 m (16 ft) from the damaged elbow. The isolation remained secure for the entire 70 day project timeframe, allowing the operator to safely complete the replacement with no product loss or interruption of service.

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