The manifold gathers production from four subsea wells and lies 270 metres deep on the seabed in the Draugen oilfield, some 140 km off the coast of Norway. The structure was lifted and brought onshore by the engineering company Kvaerner Oilfield Products to its yard in Agotnes for non-destructive examination and repair.

Shell’s Norwegian arm, Norske Shell, wanted to carry out ultrasonic inspection of the hubs, the forged stainless steel components through which the pipelines connect to the manifold, and the welds which bind the components together.

AGR, which was responsible for project management and providing inspection personnel, turned to Phoenix to design and manufacture ultrasonic equipment and design the inspection process. During the 14-week project, the two companies built up a team of 10 inspectors between them.

Jim Knowles, applications manager at Phoenix and inspection supervisor, said the inspection was complicated by the nature of the material to be tested and the complex geometries involved. Speed of reaction was also a priority in order to minimise lost production time.

“The hubs are forged from super duplex stainless steel,” Jim explains. “While this type of material is excellent in resisting corrosion from seawater, its coarse grain structure makes it particularly difficult to inspect. This was overcome largely by the use of longitudinal wave transducers and ultrasonic scans in all directions.

“The inspection also had to be carried out from deep within the bores of the hubs. The unique scanner design meant it could be used in bores of different diameters. It also took into account the steps and angles for the examination of the steel hubs, the weld and the sides of the pipes beyond.”

Angled longitudinal wave transducers were used throughout the inspection consisting of various angles and creep waves. Additional lower frequency transducers were urgently manufactured by Phoenix to aid in the inspection of the thicker forged sections of course grain material, ensuring near 100 per cent volumetric coverage. While developing the inspection method, the procedures and calibration of equipment were closely monitored by the inspection authority Det Norske Veritas (DNV) and its assistance ensured references and sensitivities could be achieved in all geometries. The final inspection procedure, approved by DNV, could be seen as a model for future examinations of this type.

Jim Knowles adds: “We were delighted to be able to assist AGR in what was a large and complex project. The collaboration between the different parties was vital to the successful outcome of this fast-moving project. All those involved responded to the challenge and worked together to provide imaginative and efficient solutions.”