Automated radiographic inspection of flexible risers. A feasibility study

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Automated radiographic inspection of flexible risers. A feasibility study

Mallett, R. / Blakeley, B. / Balachandran, W.

Flexible risers are flexible pipes used to bring oil from oil wells deep underwater to the surface, where it can be processed by Floating Production, Storage and Offloading (FPSO) installations. Flexible risers consist of a number of layers of steel and polymer that have a complex structure and some layers are shielded by others, making non-destructive testing particularly difficult. This paper presents some experimental radiography of a sample flexible riser. Both single-wall and double-wall techniques were used with X-rays and gamma rays with both computed radiography imaging plates and an amorphous silicon flat-panel detector. The layer of the riser that is of particular interest is the pressure armour, which is the layer designed to withstand the internal pressure. It is a layer that is particularly difficult to inspect, as it is shielded by a metallic layer on both sides. The resulting images were used to develop an image processing technique designed to detect separations in the pressure armour, which is also presented here. The technique is based on the use of the Hough transform to detect nonstructural lines in the image. This technique has been tested on a defect simulated by image processing and an artificial defect introduced to the flexible riser sample. The technique was found to be successful in detecting the artificial defect in a set of images, with only 4 % of misclassification, which were all false positive results.