Composite repairs are increasingly used in the oil and gas industry, for temporary repairs and for permanent repairs provided long-term performance is demonstrated. Composite repair systems are mainly used for onshore pipelines or offshore topsides. They are generally made of fibers tapes (aramid, glass …) impregnated with epoxy resin and then wrapped around the pipe. The number of fibers tapes layers and the repair length is determined from design calculations following standards such as ISO/TS 24817 or ASME PCC-2.
For subsea application of composite repair, five main issues must be considered:
pipe preparation: coating removal and surface preparation are necessary to ensure adhesion of the repair,
resin properties: the resin working time must be extended to allow fibers tape preparation above water and application under water,
repair performance: it must be demonstrated that underwater application do not affect repair strength,
repair system application: this is mainly a manual task today which can be performed by divers but is not applicable for deepwater,
design to lateral buckling and collapse: specific design criteria and limit states of composite repair must be determined for deepwater.
Several tests of divers' assisted underwater applications have been performed under third party supervision, using a specifically developed epoxy-resin. The experimental database covers repairs of through thickness defects and localized wall thickness reduction up to 80%. All tests results were comparable to results obtained for above water repairs and evidenced that the original pipe strength was fully restored.
In parallel, a specific tool has been developed to apply automatically the repair system with two main objectives:
to improve quality and repeatability of the wrapping operation, with applying constant tension and winding path,
to allow diverless (ROV) applications, which is a pre-requisite for deepwater applications.
This tool has been already tested underwater in the " semi-automatic" mode (operated by divers) with a positive feedback.
Composite system is, technically and economically, a promising way to repair subsea pipelines. There are no more restrictions to consider composite repair systems for shallow water applications. Additional tests with ROV, as well as collapse and bending resistance tests are now to be performed to open the way to deepwater repairs.