Getting to the bottom of subsea repairs

03/30/2016


Major pipeline repairs

A damaged pipeline leaking in deepwater highlights the importance of a sound maintenance strategy as well as an established procedure for repairs. Courtesy: OceaneeringMajor repairs require the damaged section of the pipeline to be removed so a replacement "spool section" can be installed using connectors that match the diameter of the pipeline. This more complicated operation requires the pipeline to be shut down, stopping its flow and the revenue it generates. Such severe damage often occurs suddenly due to an accident or extreme weather conditions. Pipeline failures also can pose a threat to the environment, so operators typically respond to them quickly.

As with minor repairs, visual and instrument inspection by divers or ROV is required for major repairs to fully assess the damage. Dredging also is usually required to expose the pipeline over the section to be removed and replaced. Spool sections can range in length from six feet to more than three miles.

For shallow water repairs carried out by divers, the operation usually proceeds with the pipeline resting on the sea floor. During deep-water repairs, subsea pipeline lifting frames are placed on either side of the section to be removed and provide support to the pipeline throughout the repair operation. For sections longer than 100 feet, four lifting frame skids are recommended, two per side—but a minimum of two are required. When the lifting frames elevate the pipe, the service vessel crane is used to support the center of the damaged section during the cutting operation. Concrete and FBE must be removed from the areas to be cut, including sufficient length to hold the pipe end flanged connectors.

A variety of methods for cutting the pipeline are available, including diver-operated "broco"-type cutters; mechanical cutters, which are best for small-diameter lines; diamond wire cutters, which are used on larger pipelines; and chop saws, which are more reliable than wire cutters and are designed for ROV use.

After the damaged pipe section is cut and removed, the exposed pipe ends must be cleaned to bare metal. Any weld seams must be milled down, and burrs must be removed from the pipe ends—both internally and externally—to ensure that connectors can be installed properly. In addition, a pipe end check tool is used to confirm the pipe's roundness. Smart flange connectors are then attached to the exposed pipe ends.

Smart flanges are mechanical connectors that provide metal grips and elastomeric seals, and are available in classes 600 through 2,500, and could be rated up to 10,000 psi. After the repair is complete, smart flanges can be tested before product flows into the pipeline and without over-pressuring the pipeline, avoiding possible damage to other sections of the aged pipeline.

The spool piece is lowered by the service vessel crane, aligned with the pipe, and the flanges are connected with bolts tightened with the right amount of torque to ensure that the ring-type joint (RTJ) gasket achieves a positive seal. In shallow water, divers carry out this operation. In deep-water repairs, the spool piece can be configured with double grip and seal connectors with hydraulic actuators that do not require extensive bolt tightening by the ROV. These double grip and seal connectors provide structural support and high-pressure seals. When activated with hydraulics, they are locked in place by mechanical slips. The spool piece with connectors is placed in an installation frame, which mates with the pipeline lift frames already in place. A laser alignment system is used to line up the spool section with the main pipe, and then the repair connectors are stroked by activating the hydraulic cylinders with ROVs. After installation is complete, the connectors are tested without over-pressuring the pipeline.

The installation frame is then removed, and the dredger is used to level the seabed beneath the repaired section. Concrete or steel mud mats are placed on the seabed to compensate for the additional weight of the connectors. The pipeline is lowered to the seabed, and the lifting frames are retrieved to the surface. The pipeline can then be put into service.

Prepare for pipeline failures

The smart clamp is fully installed on the subsea pipeline. Courtesy: OceaneeringGiven the consequences of subsea pipeline failure, it is important for operators to establish regular pipeline inspection, maintenance, and repair programs to maintain asset integrity. Even after taking these precautions, pipeline failures can occur. To be prepared to respond to these incidents, pipeline repair experts recommend that operators maintain emergency pipeline repair inventories including one clamp and two smart connectors for every size of pipeline in operation. For deep-water pipelines and remote locations, it is good practice to have pipeline lift tools as well as ROV tools for pipeline repair kept on hand and in good working order.

In addition, it is important for operators to understand that pipeline repair is a complex operation that requires engineering, logistics, and deployment of a range of equipment besides clamps and connectors, including a vessel to support lifting, diving, and ROV operations, as well as dredgers, ROVs, and associated tooling. Qualified divers with proper training in pipeline repair, and ROV operators experienced in similar operations, must be assembled and managed, including support staff. Additionally, specialized equipment may need to be modified or built from scratch and deployed on short notice to meet the project's requirements.

Because of these factors, project management is an important aspect of pipeline repair operations. Pipeline owners can benefit from having a single project manager who can effectively coordinate the activities of numerous service disciplines. Suppliers that can provide a range of pipeline repair services and equipment also can improve efficiency through better communication, a common safety program, and shared accountability for results. It also is important for pipeline repair contractors to have facilities close to each area of operation to enable quick response and ongoing support for the repair effort.

Meeting pipeline repair challenges

As pipeline systems age and capital budgets for replacement lines are reduced, operators face the challenges of maintaining product flow and protecting the environment. Fortunately, technology and services are available for regular pipeline inspection and maintenance as well as unplanned repairs, in shallow and deep-water conditions. To prevent lengthy downtime, operators should have plans in place to repair their pipeline, and should build relationships with pipeline repair experts who can respond quickly when a leak is detected or a pipeline fails.

John Charalambides is director of business development at Oceaneering Connection Systems.


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