This paper describes the method and equipment developed to allow ROVinstallation of a grout-filled reinforcement sleeve on a damaged 18" subsea gaspipeline at a water depth of 2,300 ft. The Williams Canyon Chief pipeline wasdamaged by an anchor drag that pulled pipeline approximately 1,500 feet out ofits original right-of-way, bent the pipeline to an unknown radius, and left asignificant dent in the side of the pipe as well. The damage did not result ina leak and the pipeline was allowed to continue to operate at not only areduced pressure, but also a minimum pressure, while repair plans weredeveloped.
Extensive research and testing determined that the pipeline could be returnedto normal operating pressure and ultimately maximum design pressure if the dentcould be restrained from flexing due to changes in pipeline pressure.Laboratory testing confirmed that cement grout inside a steel sleeve installedaround the dent would provide the necessary reinforcement.
A specially designed, ROV friendly repair sleeve was developed to match thepipeline curvature that was estimated by side scan sonar imaging andphotogrammetry. The sleeve was fabricated as a straight cylinder but the endswere angled and positioned off-center to account for the pipeline curvature.The sleeve was split horizontally so that all clamping screws were vertical. Anarticulated spreader bar, ROV operated pull-down winches, and a large syntacticbuoyancy module allowed the ROV to control the entire installation after theequipment spread was landed on the seafloor.
A project specific metrology tool that measured the curvature of the pipelineat 24 points was built and landed on the pipeline to confirm earlier calculatedestimations. An ROV video record of the gauge readings was then used in theshop along with the metrology tool to fabricate a dimensionally correct mock-upof the pipeline. This mock-up was then placed into the repair sleeve to confirmthat it would fit on the pipeline.
Composite systems are a generally-accepted method for repairing corroded andmechanically-damaged onshore pipelines. The pipeline industry has arrived atthis point after more than 15 years of research and investigation. Because theprimary method of loading for onshore pipelines is in the circumferentialdirection due to internal pressure, most composite systems have been designedand developed to provide hoop strength reinforcement. On the other hand,offshore pipes (especially risers), unlike onshore pipelines, can experiencesignificant tension and bending loads. As a result, there is a need to evaluatethe current state of the art in terms of assessing the use of compositematerials in repairing offshore pipelines and risers.
The paper presents findings conducted as part of a joint industry effortinvolving the Minerals Management Service, the Offshore Technology ResearchCenter at Texas A&M University, Stress Engineering Services, Inc., and fourcomposite repair manufacturers to evaluate the state of the art usingfull-scale testing methods. Loads typical for offshore risers were used in thetest program that integrated internal pressure, tension, and bending loads.This program is the first of its kind and likely to contribute significantly tothe future of offshore riser repairs. The end result of this study was thedevelopment of a carbon-fiber repair system that can be easily deployed toprovide significant reinforcement for repairing risers. It is anticipated thatthe findings of this program will foster future investigations involvingoperators by integrating their insights regarding the need for composite repairbased on emerging technology.