An international operating company detected a leak during an annual ROV inspection of a water injection (WI) pipeline offshore Angola in the Gulf of Guinea. The pipeline owner made the decision to repair the damaged line using clamps, but there were multiple challenges involved in executing the repair. First was the depth of the pipeline, which was on the seabed across an area that ranged from 1,170 m to 1,410 m (3,839 ft – 4,626 ft). Additional challenges included potential complications for clamp installation because of the location of the pipe welds and the physical condition of the pipe, which had experienced considerable wall thinning in multiple areas. Bringing the pipeline back into safe service required repairs to the aging pipe within a scope of work that included site preparation, the installation of two 12-in clamp connectors, and inspection services following clamp placement to verify proper installation.
Because there were welds in the WI pipeline, there was a risk that the clamp installation site would correspond with an area of the pipe that was welded, which would impact the ability of the clamps to fit snugly over the damaged area. Survey data were cross-referenced with the client's data to determine that the weld locations would not interfere with the installation. Coating removal was critical, so a purpose-built mechanical tool was designed to prepare the pipeline for clamp installation. The project also required finite element analysis (FEA) to confirm that the pipeline could withstand the seal load applied by the repair clamps.
The project was carried out in three steps. The objective of the first step was to prepare and stabilize the seabed to ensure it could bear the weight of the clamp installation frame and the impact of the ROV working nearby. The second phase focused on preparing the repair locations for installation of the clamps, a process that included coating removal and surface cleaning to return the WI pipeline to bare metal finish in the clamp areas. The third phase was the preparation and installation of the 12-in repair clamps. This included the inspection and spot cleaning of pipeline surfaces, clamp installation, and clamp seal verification.
The two clamps were successfully installed and passed pressure testing in February 2020, enabling the operator to bring the WI line back online and functioning safely at reduced pressure.
This repair employed the highest-pressure clamp of this type installed to date (138 bar / 2,000 psi).