Subsea 3D Video Survey of Mooring Chains - Improving Safety, Effectiveness and Efficiency

Abstract

Abstract Production of oil & gas using moored Floating Production Storage and Offloading (FPSO) units has been experiencing a significant growth. As of July 2022, there were 209 FPSOs in use around the world. In addition, there are many moored FSOs and CALM buoys. Moored facilities are located in many different operating areas, environments and water depths. This growth has resulted in a major challenge to operators, mooring component suppliers, regulators, and Class Societies to assure the integrity of these facilities. Mooring chains are safety-critical systems for FPSO and moored facilities in general. They are subject to significant environmental and structural loads as currents, waves, drag forces but also impacts, abrasion with the seabed or the fairlead. Failures in a mooring line can result in dramatic consequences for the safety, the environment, and the productions. Periodic inspections are mandatory and can be performed in air or in situ. Several techniques are available, with their advantages and limitations. This paper discusses the motivation and business driver for developing and implementing a new and cost-effective in situ inspection methodology. The approach is based on 3D video survey performed by inspection class ROVs and robotic crawlers that allows to gather critical integrity information in a safer, effective Due to the conditions and the geometrical configuration, the Subsea 3D Survey of Mooring Chains is challenging. However, by using advanced photogrammetry, and laser triangulation techniques (Video Laser Scan™ or VLS™), it is possible to solve such a challenge from simple ROV (Remotely Operated Vehicles) flights and robotic crawler runs when it comes to tiny spaces (Fairlead). The VLS™ sensor (HD camera and Laser Line Projector) is mounted on the ROV that flies along the chain: the laser line scans the links' surface, and four linear paths along the chain ensure 360 degrees of coverage. The ROV is in flying mode and needs to follow the chain at an average distance of about 1m. The output is a high-accuracy Point Cloud from which dimensions of the links can be computed, as well as the 3D mapping of anomalies such as corrosion pits. Examples are presented, and comparison is made between traditional and new inspection methodologies based on recent mooring chains' inspection campaigns to demonstrate the improvement of inspection effectiveness and efficiency.