High-energy computed tomography for inspection and monitoring of flexible riser

Abstract

Flexible risers have been widely used in the offshore oil and gas industry and have many applications, such as production, gas lifting, or gas and water injection. The structure comprises several metal and polymer layers, which allow it to withstand a sizeable bending curve and high internal pressure. Therefore, guaranteeing the integrity of flexible risers throughout their useful life is extremely important. It requires developing and applying effective inspection and monitoring techniques, particularly emphasizing the tensile armor layers. This work evaluated the ability of the High-Energy Computed Tomography (CT) Technique to detect internal defects such as cracks, breaks, and fissures in the riser layers. A flexible riser sample of approximately 2 m in length and 281 mm in external diameter was scanned using a tomography system consisting of a 6 MeV Betatron and a set of 14-bit A-Si digital detectors. The images were acquired in 360° with angular steps of 2°. After acquisition, the images were reconstructed, and 3D models were built for qualitative and quantitative evaluation. Through the segmentation process, the metal layers of the flexible riser could be analyzed individually. Defects were found in the tensile armor layers, indicating ruptures and cracks and the onset of pitting. The results strongly suggest that computed tomography can be used as a non-destructive technique for inspecting flexible risers, with good efficiency in detecting defects, and that its application can be extended to field tests.