FRC: A low-cost service robot for subsea flexible risers

This paper presents the design and development of a semi-autonomous low-cost underwater service robot for subsea flexible risers, used for supplying oil from the deep sea to the offshore platforms and floating production, storage and offloading vessels (FPSO). The robot is designed in a modular way allowing flexibility and variety in use. It can provide various types of services according to user needs, such as carrying equipment for inspection and deploying tooling for repair. The robot moves along the riser like an inchworm does, thanks to a simple, yet versatile crawling mechanism. In addition, the robot can rotate around the riser indefinitely by using a similar principle. Novel under-actuated end-effectors have been conceived and developed to firmly hold the robot on the riser during locomotion, rotation or operation, without affecting riser integrity. In principle, the current design could operate up to 2000m sea depth with minor modifications. In this study, the service robot carries and deploys digital radiographic equipment for the volumetric inspection of flexible risers. Several preliminary tests, as well as a series of underwater tests proved the robot's encouragingly positive performance.