Composites offer effective offshore pipe repair alternative

Neptune Research Inc. (NRI), has been manufacturing water-activated, fiberglass composite repair systems since the mid-1980s, and has a track record in repairing various offshore pipes and risers, both above and below the water line. Because the pre-impregnated wrap is water activated, it is ideal for application under water, and application of the various epoxy systems has been made friendly to the applicator by using innovative self-mixing application tools designed for both underwater mixing and application. In addition to being applicator friendly, the pre-impregnation process is micro-controlled, which guarantees that the fiber to resin ratio is correct and consistent for each application. This insures that the strength obtained during qualification and quality control testing is same as strength obtained in the field.

Case studies

One company in Thailand recently used the composite repair system Syntho-Glass XT, which is manufactured by NRI. The application came at a critical time for this offshore company, since the wall loss on this 32-in. riser was such that the only other option available was a full cut and replacement of the pipe section needing repair. The damaged pipeline was on an offshore oil rig which supplies the nation’s power plants with fuel. A shutdown would have cost the country roughly $125,000 per hour in lost production, or more than $3 million a day. Replacing the pipeline would have been a major undertaking that would have lasted months and cost millions. Heavy equipment would have needed to be shipped to the oil rig to make the repairs. Since taking the pipeline out of operation would have been financially crippling, the operator decided instead to use a composite repair solution.

The Viper Skin composite wrap provides an effective repair alternative for subsea pipelines.

To promote adhesion, the pipe was cleaned using sand/grit blasting and power tools to remove rust, paint, and other foreign matter. All pitting and corrosion defects on the pipe were filled with a two-part, high-compression-strength epoxy putty to restore the pipe to its original geometric shape, and also to help transfer the load from the pipe to the wrap system. It was then coated with Syntho-SubSea LV epoxy, a high compression-strength, two-part Kevlar reinforced epoxy. The two-part epoxy stops corrosion, promotes bond between the pipe and the wrap, and provides a load transfer medium engineered to cycle and work under extreme pressure strain and aggressive pressure cycling. The line was then wrapped with Syntho-Glass XT, a high-strength, fiberglass composite wrap which provides structural integrity to the repair. The composite product was successfully applied over a length of approximately 10 ft (3 m) to restore this pipeline back to its original design pressure of 1,580 psi (109 bar).

Using the composite repair system, the operator was able to have this pipe repaired in less than 36 hours, a job that otherwise could have taken months to complete. A full pressure test of the repair was performed at 1,700 psi (117 bar) for four hours; the pipe resumed full operation later that afternoon. The gas field is now operating at full capacity of 630 MMcf/d.

Petrobras is another company successfully using composite repair systems on offshore pipe. The range of applications varies by location, and includes both topside repair as well as subsea applications. Diving teams have completed composite repairs for Petrobras with the Syntho-Glass XT repair system in waters down to 100 meters (328 ft). The ability to perform these repairs safely with composite repair systems avoids the costs and dangers of underwater welding or suspending production. It also means safer application techniques for the diver and a more economical solution for the operator.

Splash zone repairs

Splash zone repairs are often a major area of concern since the constant wet/dry atmosphere can cause severe corrosion which may damage the coating. Impact from debris can be an issue, too. This is another area where composite systems are effective. Many of the corrosion coating systems which perform well are not always the best system when it comes to impact or abrasion resistance (such as petrolatum tapes or visco-elastic coatings). By combining an effective corrosion coating system with a protective outer layer of composite material, one can get the benefit of the corrosion coating system and gain a superior mechanical barrier that is both light and strong. The Syntho-Shield system provides such a system for coating repair and protection of riser pipes. The composite outer wrap can be combined with any number of corrosion coatings to meet the coating specifications and to provide a tough, durable composite shell. This helps insure a long-lasting coating life. It also helps prevent the formation of potential corrosion cells which could result in the requirement for a full repair system.

Pipes with holes also may be repaired with composite materials. That said, one cannot overestimate the importance of application experience; a full understanding of composite material capabilities; and proper design. All these factors are critical to insure that the repair system is adequately designed and properly installed. The repair of through-wall defects in a pipe becomes more of an art and requires a skilled technician with experience in applying composite repairs.

Many of these applications have been completed, but usually are considered a temporary means to keep the leak sealed (or at least to slow the leak to a manageable flow), and to reinforce that section of pipe which has lost its original wall strength. One such repair was carried out on several caisson pipes on an offshore platform in the North Sea. The caisson piping had numerous small holes throughout the length of the pipe extending from below the splash zone to the floor of the platform.

The area to be wrapped with the composite was properly prepared to insure adequate bond strength of the repair to the host pipe so the wrap would contain and keep the leak sealed. Surface preparation is crucial for any application where the composite wrap is expected to contain the pressure of the pipe and to keep leaks sealed. Once the surface was properly prepared, the wrap was applied the length of the damaged pipe. After curing, the wrap was painted for UV protection as well as to match the color of the platform piping.

Successful applications

As composite repair usage continues to rise, we will continue to see advances in technologies, new innovations, and new regulations and guidelines for the industry as a whole. There are numerous standards organizations that now recognize composite repair systems as acceptable and suitable repair options. This opens the door wider for operators to continue to use composites in their maintenance programs, and to be comfortable that it is an approved alternative with sound industry backing. This is not a blanket approval for all composite repair systems to be considered for every repair, but it does lay out specific guidelines that allow the operator to make an educated decision based on proper qualification testing and sound engineering practice. Any system being considered for a repair project should be thoroughly reviewed to insure all qualification testing has been completed and that the composite in consideration is compatible with the type of defect and repair being addressed.

Composite systems present new, available options for maintenance or repair for offshore structures. As material, design and capabilities advance, the possibilities increase. Regulatory acceptance and development of specific composite repair standards continue to change the mindset of operators, and open doors to a wider audience for the use of these repairs. Composites are beginning to move from a “Plan C” option to become a more recognized and generally more preferred alternative. It will only go up (and deeper) from here.