Riser Inspections Using a Self-Propelled Ultrasonic Solution

Abstract Inspecting offshore risers using in-line inspection (ILI) technology is inherently complex and involves elevated operational, safety, and environmental risks. These complexities increase significantly when risers were not designed with conventional pigging facilities (launchers/receivers) or when operating conditions preclude product-flow–driven inspections. Many aging offshore assets in the Gulf of Mexico fall into this category, where legacy configurations and limited access can render traditional pigging infeasible or cost prohibitive. In 2024, a major operator managing multiple offshore assets in the region identified two 8" risers with heightened risk of external corrosion in the splash zone, driving a need for high-confidence inspection data from the splash zone to the seabed to support continued safe operation and long-term integrity planning. Ultrasonic testing (UT) was selected as the primary inspection modality due to the risers’ exceptionally heavy wall thickness (1.250–1.500"), which is beyond the optimal range for certain magnetic technologies and well-suited to UT provided an appropriate liquid couplant is used. Diesel was chosen as the couplant to ensure reliable acoustic transmission and consistent wall thickness measurements without disturbing normal operations. However, the risers were categorized as unpiggable due to three decisive constraints: (1) lack of launchers and receivers, (2) a single topside access point per riser, and (3) the operator’s preference to avoid external circulation equipment (pumps or support vessels). These constraints necessitated an inspection approach that was independent of flow and compatible with the existing platform layout, with minimal temporary modifications and no subsea intervention. To address these constraints and mitigate risk, the team developed and deployed a tethered, self-propelled UT inspection solution. The system comprised an electro-crawler propulsion unit for controlled bidirectional movement; a rigid UT scanner ring carrying 96 sensors to deliver high-resolution circumferential coverage and wall thickness mapping; odometer segments to synchronize axial position with probe excitation and data acquisition; and transformer/interface modules for robust topside power, control, and real-time data visualization. The tethered configuration provided operators with immediate feedback on tool performance and data quality, enabling repeat passes, targeted parameter adjustments, and responsive anomaly verification—capabilities not typically possible with free-swimming tools. Prior to offshore mobilization, a structured validation program was executed. In-house functional checks verified mechanical integrity, correct parameter sets, sensor alignment, motor performance, crawler pull/pull-back forces, odometer accuracy, and tool orientation using a pendulum system. A blind test at a specialized facility near Houston utilized a heavy-wall test pipe with artificial defects to confirm detection sensitivity, circumferential/axial positioning fidelity, and sizing accuracy under representative conditions. The tests demonstrated reliable identification and precise sizing of metal loss features across the UT color scale—where color intensity correlates to remaining wall thickness—establishing confidence in the system’s resolution and repeatability for the intended application. The offshore campaign was conducted in Summer 2024 within a planned shutdown window. After setup of the office habitat, umbilical winch, and topside control, the risers were filled with diesel to provide consistent coupling. A customized blind flange with a low-friction feed-through socket sealed the launcher spool around the tether to prevent product egress while minimizing crawler load. The tool train was inserted through the single topside entry point, advanced to the seabed, and then retrieved, generating two complete datasets per riser (down and return runs). Real-time visualization supported parameter refinements and ensured comprehensive coverage of critical elevations, especially the splash zone. Both risers were inspected without subsea modifications and without reliance on flow, fulfilling the operator’s constraints and minimizing logistical complexity. The solution yielded high-confidence UT datasets that clearly indicated wall thickness variations and localized corrosion, enabling targeted maintenance planning and risk mitigation. Operational benefits included reduced support equipment, lower environmental impact (no fluid displacement beyond coupling requirements), and improved safety due to precise tool control and transparent data quality assurance. More broadly, the project demonstrates that tethered, self-propelled UT inspection can extend in-line inspection to risers traditionally deemed unpiggable, delivering actionable integrity data under strict access and operational constraints. The approach offers a practical template for operators managing aging offshore infrastructure in harsh environments, balancing inspection rigor with cost, safety, and sustainability considerations.