Faced with the unprecedented task of inspecting the world’s longest subsea gas pipeline in a single run, ROSEN developed a customized RoCorr•MFL/SIC tool. Over and above its unparalleled length of 1,173 km and the resultant tool wear issues, the Langeled pipeline connecting Norway and the UK posed additional challenges, notably its multi-diameter design and high product flow velocity.
In line with the Langeled project objective of gathering accurate corrosion data, the RoCorr•MFL/SIC combines the two complementary corrosion measurement methods magnetic flux leakage (MFL) and shallow internal corrosion (SIC). Whereas MFL is a reliable method for determining relative wall loss and the geometry features of metal loss in pipelines, SIC enables absolute measurements of internal corrosion defects.
The simultaneous application of the two methods ensures an exceptionally high probability of identification (POI), reliable discrimination between internal and non-internal features, and high accuracy in depths, length and width sizing of internal corrosion defects. The RoCorr•MFL/SIC combo tool is thus a highly suitable method for monitoring the degradation process.
To overcome the tool wear issues arising from the exceptionally long inspection run, the RoCorr•MFL/SIC was equipped with three sealing planes, special tool centralization, and guiding disks to reduce cup wear and improve run behaviour. The multi-diameter challenge was met by means of customised polyurethane cups which were designed to limit tool wear during the passage through the narrow section while still providing sufficient sealing capabilities in the wider section of the pipe.
Finally, a speed control unit (SCU) was used to control the bypass flow, enabling a pre-programmed speed and eliminating the need for a costly product flow rate reduction. Since no subsea pipeline of such proportions had ever been inspected in a single run before, the RoCorr•MFL/SIC is a world record holder.