RiserSure: Automated Deployment of Digital Radiography for Subsea Inspection of Flexible Risers

Abstract

Flexible pipes are used as risers to carry oil and gas from sub-sea wells to Floating Production Storage and Offloading vessels. Due to the harsh nature of the environment, these risers are subject to fatigue over their lifetime. It is important, as part of their integrity management, that regular in-service monitoring is undertaken to track how the asset ages. Current inspection methods for flexible risers are limited. Only radiography can inspect the multiple layers within a flexible riser to produce a volumetric inspection. Automated underwater digital radiography improves on traditional radiography by allowing a shorter inspection time. This paper presents the design and development of a new automated, underwater digital radiography inspection system prototype to survey flexible risers at depths of 100m. This is a cost effective solution using a commercially available underwater Gamma radiation source holder and a high definition, linear digital radiography detector housed in a submersible vessel. The sub-sea deployment of a linear detector for underwater inspection of flexible risers is reported for the first time. The use of a linear detector array offers greater sea depth capability, in a smaller package, and the ability to cope with the high radiation energy demands of the Gamma source compared to flat panel detector solutions. Deployment has been achieved by implementation of a bespoke robotic scanning system that can accurately control the source and detector motion. The prototype was mounted on a flexible riser during shallow water sea trials. Preliminary results are presented which show that the internal inner and outer tensile armour layers in the riser have been successfully imaged.