SHARJAH, UAE – Abu Dhabi Marine Operating Co. (ADMA-OPCO) has contracted Unique Wellube, a division ofUnique Maritime Group, for the supply and engineering of mechanical seal plugs for a significant pipeline isolation project.
An ADMA-OPCO 8-in. subsea riser was found to have some damages that would require a weld repair at the splash zone on the complex side. The plan was to cut 1.5 m (5 ft) of the riser to below the damaged area and to weld a new spool in place. Since welding was involved, either the pipeline had to be free of hydrocarbon fumes or a positive isolation had to be created to prevent the fumes from reaching the welding area. However, there was no break flange available in the repair location to isolate the pipeline to conduct the repair works.
ADMA’s initial plan was to pig the riser to make the riser free from hydrocarbon fumes. However, the estimated cost to execute pigging was comparatively high and the time required to ensure that the riser was free of hydrocarbon fumes would be very long, making the riser non-functional for the duration.
ADMA-OPCO approached Unique Wellube to look for a cost effective and quick turnaround solution to the 8-in. riser weld problem.
Using Wellube’s experience in line stops and plugging, Wellube’s engineers along with ADMA’s technical team, decided to look at feasibility of using an extended retractable mechanical seal plug. The plug would have to be installed at a distance of 2 m (7 ft) from the top of the riser. A joint risk assessment was conducted and it was decided to go ahead with a workshop trial to study the performance of the extended plug.
Based on the outputs of the meeting and the risk assessments, Unique Wellube designed and manufactured an 8-in. extended plug.
The plug was inserted into a mock-up pipe piece, at a depth of 2-m (7-ft) distance from the top of the pipe and tightened manually from the top. To ensure the integrity of the plug, fire foam was injected into the mock-up pipe for half a meter from the top of the seal plug, creating a head pressure, and kept under observation for three hours. Subsequently, inspection was carried out on the other side of the plug and it was found to be 100% leak proof.