Selection and Validation of Flexible Riser Inspection Method

Abstract Corrosion of flexible risers armor wires resulting in wire breakage with subsequent rupture is a credible risk for the offshore energy industry. LLOG has been operating the Who Dat flexible risers since 2011. After 12 years of service, a baseline for annulus condition had not been conducted due to the inspection and monitoring constraints from riser configuration. This paper outlines approach to select and validate suitable inspection technologies to reliably identify tensile armor wire anomalies. The annulus condition can vary significantly for each riser and directly affects the integrity of the armor wires. External non-destructive examination tools were used to assess the armor wire condition and annulus environment of the Who Dat flexible risers since annulus testing is not feasible. Inspection locations were determined based on a risk assessment considering the credible corrosion, fatigue and overstress degradation mechanisms for each riser. The inspection allowed for reliable detection of defects and corrosion on the outermost layer of tensile armor wire, and gather information on the condition of the annulus. Traditional annulus testing methods are not feasible for the LLOG Who Dat flexible risers due to the riser end-fitting hang-off configuration at the hull pontoon and the shared annulus venting system. Additionally, the production risers with 58mm thickness of outer sheath and foam insulation pose inspection challenge. For uninsulated risers, a Magnetic Eddy Current (MEC) based subsea solution was one of the tools selected. This technology, which had been validated and deployed offshore by multiple operators worldwide, offers the key advantage of rapidly scanning large surfaces and reliably detecting armor wire defects. MEC technology was supplemented by a frequency-based ultrasonic measurement system to assess the flooding status of uninsulated risers. For insulated flexible risers, a bespoke High Frequency Eddy Current (HFEC) subsea crawler was selected. The tool underwent extensive onshore validation to detect armor wire defects on a representative insulated sample prior to offshore deployment. The HFEC scanner is used to screen for localized defects including corrosion, cracks, and wire gaps regardless of annulus flooding condition. The inspection data was processed in real time, allowing for an immediate assessment of the asset's integrity and requirement for additional inspection locations. Adoption of available inspection techniques for flexible risers varies significantly based on method and riser configuration. Although, eddy current inspection methods offer the key advantage of rapidly scanning large coated or uncoated surfaces and reliably detecting defects, they have been previously implemented offshore to a limited extent. The approach presented in this paper describes a road map for qualifying and incorporating inspection technologies into a comprehensive flexible riser integrity management program.