Non-Metallic Clamp for Flexible Risers

Abstract A novel non-metallic clamp for flexible risers with breached outer sheath in the splash zone has been developed, qualified, and installed to restore annulus integrity and enable riser lifetime extension. Flexible riser outer sheath breaches in the splash zone or aerial riser portion have been experienced by operators and reported to occur by Sureflex JIP, due to natural degradation (i.e., UV aging and fatigue), dropped objects, or blocked vent ports of riser end fittings terminated topside. An outer sheath breach in the splash zone or aerial riser portion exposes the structural carbon steel wires to rapid corrosion due to oxygen inflow at the breach location, and because existing cathodic protections are not effective above the mean seawater level. Rapid corrosion in turn decreases both riser strength resistance to pressure and tensile loads, and riser corrosion fatigue resistance, which over relatively short period of time may lead to loss of riser containment. Clamping of the breached outer sheath location has been historically used to mitigate that risk of loss of containment with the use of steel clamps of various design. Three steel clamps were installed over a longitudinal-seam-weld-outer-sheath repair performed at riser installation over the course of a few years, with a new leakage discovered after each clamp installation. This experience has led to the realization the outer-sheath stiffness transition in the vicinity of the steel clamp edge and clamp tightening have driven initiation of new breaches nearby due to the degraded outer-sheath-seam-weld repair. This realization in turn inspired the development of a novel, cost effective non-metallic clamp that eliminates the sharp stiffness transition caused by metallic clamps. This paper describes the development, qualification and installation of a novel non-metallic clamp to enable the lifetime extension of a flexible riser described in OMAE 2023-101167 1. The paper presents the transition from technology readiness level TRL-0 (basic research) to TRL-6 (system installation). It presents the logic of material and component functionality selection, failure mode identification, prototyping, validation testing, system integration, installation, and lessons learned. It concludes with recommendation on scalability of the non-metallic clamp use and further development on adding venting functionality.