Thunderhorse project benefits from field-joint heat and coat technology

Operating vertically in the J-lay tower, this latest Radyne solution is also being used to treat the hang-off [2] collars located centrally on the pipe.

Having already provided induction heat and coat technologies for the challenging Blue Stream J-lay project in 2002 – a contract that involved the application of a three-layer girth weld coating on a vertical pipe within the confined space available onboard the upgraded lifting barge – Radyne’s technical team set about developing a solution for Hereema Marine Contractors (HMC) for Thunderhorse. The system was required to apply FBE and CMPP adhesive to 1270-mm long field joints with pipe diameters of 12.75in, 10.75in, and 8.625in, as well as ensuring all the collar faces were coated. To complete the process, a 75-mm thick extruded polypropylene layer would be applied by equipment supplied from Norway.

In considering a number of options, including a modified version of the company’s Merlin solution as used on Blue Stream, and a single shot heating/multi-head coatings design, Radyne decided that, in view of the field joint length, the complexities of incorporating the hang-off collar, and the difficulties of working in a vertical plane, a new system was developed: the company’s scan-heater was combined with a variable powder-coating system to ensure that the varying pipe diameters and hang-off collar faces were properly coated to the specified thicknesses. The FBE layer was specified to be in the range of 200-300microns, followed by a 150-micron adhesive layer. The Radyne heat-and-coat unit would apply the first two layers with the third, 75-mm, polypropylene layer being extruded.

Computer-controlled, and designated the Pilgrim 2, the Radyne system was mounted on a hydraulic-actuated robotic arm in order to provide the required level of scanning and movement. The three elements required to complete the coating of the joint were then sited in the lay-vessel’s J-lay tower, where space was understandably at a premium. The blaster, the scan-heating unit, and the extruder all operate in sequence, in a confined area, with a minimum of manual interference.

The system was commissioned in November, 2004, and to date all 311 joints on the flowlines have been successfully completed; coating the 403 SCR joints will be completed this month (June).

Notes:

1. Scan heating technology is a system of progressively heating a pipe by passing it through a narrow-band induction coil, or by passing the induction coil along the pipe. The coil is said therefore to ‘scan’ the pipe. When scan heating and coating a pipe bend, for example, the pipe is progressively heated and coated as the unit traverses the bend. The usual method is to heat the to temperature in a large oven, and then mount the heated bend on mandrels and coat the bend by hand.

2. A hang-off collar is a cast steel insert which is welded onto a pipe string, the purpose of which is to suspend the pipe string vertically in a J-lay tower of a lay vessel while the string itself is welded to the pipeline prior to lowering into the sea. This is carried out progressively, and the pipe strings are usually between 24m and 60m long.

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