Problem
A 22″ offshore export riser pipeline was experiencing sever external corrosion over a 3 meter section of pipe which required a repair to continue operations without risk of failure. The corrosion issue was on the main line, but also extended onto the secure clamp.
Conditions
With the presence of the extreme corrosion on the area, a repair was required in order to sufficiently reinforce the thinned area to prevent failure and keep the system in working order. The API 5L X70 pipeline of nominal thickness of 0.508-inch operates at a continual pressure of 1,500 psi (103 bar), so the design of the repair system had to account for this, plus safety factors. Due to location, all work was completed on a specially built scaffold with limited working space.
Solution
Due to the heavy external corrosion, surface preparation was limited to hand preparation techniques for fear of rupturing the line with the aggressive surface preparation methods. The corrosion pitting was filled using high compression filler to return the pipe back to its original geometric shape and smooth all surfaces. The filler’s high compression strength liquid epoxy which protects and effectively halts future corrosion while also providing a load transfer medium from the pipe to the composite wrap. An engineered carbon fiber composite repair system which was developed for the repair of high risk pipelines was used for the repair. This high strength composite material utilizes a specialized epoxy system that provides excellent physical properties even in high temperatures conditions while also giving a long working time for the installation on large diameter pipe in hot environments. To help give the riser some stiffness in the vertical direction, two layers of the carbon fiber was applied vertically along the length of the pipe. In addition, fibers were also run vertically from the outside face of the clamp, up unto the main pipeline. The engineered carbon fiber composite wrap was then applied circumstantially at the calculated number of layers over the 9’10” (3m) length and tying into the vertical strips from the clamp, thus fully restoring the integrity of the pipe for continued operation.
Result
In only a few hours, the client was able to repair and restore the section of pipeline to higher than its original design pressure. The pipe could remain in service without the need to reduce operating pressure, thereby fully repairing and reinforcing the section while maintaining the full operating specifications.
