Flexible risers are typically used for transporting oil from the sea bed to offshore platforms and Floating Production Storage and Offloading (FPSO) units but there is currently no method of examining in situ, the cross section of underwater risers and flow lines to ensure their continued reliable high-integrity operation.
TWI is leading a consortium, known as FlexiRiserTest, which is developing a prototype system for the inspection of flexible risers. The prototype uses an external gamma radiography technique comprising an oppositely positioned gamma source and marinised digital flat panel detector to image the internal walls of flexible risers. Existing radiography-based inspection of underwater structure uses film or phosphor plates which have to be returned to the surface for development and processing.
It is believed to be the first time that a digital flat panel detector has been used for underwater radiography inspection. The application of a marinised digital detector allows for rapid production of radiographic images of the riser, which can be instantly relayed via an umbilical to a host computer at the FPSO.
A robot has been developed for deployment of the radiography based inspection technique. The robot is capable of crawling along the external surface of the flexible riser, and is also able to rotate 360° about the riser axis so that the riser can be completely imaged. Since this new inspection technique facilitates the acquisition of a significant amount of images, Automated Defect Recognition (ADR) algorithms have been developed to help reduce the number of images presented to the operator. Specifically, ADR has been demonstrated to detect broken tensile wires in flexible risers. The inspection technology has been tested to a depth of 20 metres, but the partners in the project are confident that much greater depths would be possible with further development.
The work is as a result of a two-year European Framework 6 part funded project, shared between nine organisations. The marinised detector technology is deployable now and can be used in underwater inspection solutions for TWI Member companies. Future work includes more underwater trials including sea trials and further development to achieve deployment at greater depth.
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