On the development of an unmanned underwater robotic crawler for operation on subsea flexible risers

Flexible risers are used for supplying oil from the deep sea to the offshore platforms and FPSOs. This paper presents the design and development of an unmanned robotic crawler for operation on subsea flexible risers. The goal is to provide the oil industry a tool for carrying equipment on flexible risers. The robot has been developed to crawl on the external surface of flexible risers. It moves along and around the riser using an inch-worm type motion. Novel under-actuated end effectors have been conceived and developed to hold the robot on the riser, without permanent influence to the flexible riser surface and geometry. In principle, the current design with modification could operate up to 2000m sea depth. In this paper, customization of the robot operation principles to carry and deploy digital radiographic equipment for the volumetric inspection of flexible risers is described in detail. Currently, there exists no equipment that can perform reliable non-destructive inspection of subsea flexible risers. Robot performance has been experimentally validated and these results are presented here for the first time. The resulting crawling performance has been proved to be independent of its environment.