TPi November 2015

Orbital welding solutions: offshore umbilicals

I n the field of offshore oil exploration, vital links between the platform or FPSO units and the seabed equipment are provided by umbilical cables. Understandably, these key components must offer impeccable quality and flawless reliability. Umbilical cables – or ‘umbilicals’ – are assemblies consisting of duplex, super-duplex or even hyper-duplex steel tubes, electric wiring harnesses, hoses and fibre-optic cables bundled together in a steel tube with a protective polyethylene casing. The final outside diameter ranges from 75 to 300mm.

wellhead equipment and manifold. They are also used for injecting chemicals designed to improve fluidity or eliminate the formation of scale and hydrates in the production stream. Two-way communication or data transfer between several platforms and the subsea installations is also conducted via umbilicals. Numerous items of Polysoude equipment are used at the various stages of umbilical construction, from the assembly of tubes coiled on spools to the assembly of connectors joining the umbilicals to the equipment. Once in position on the seabed, especially in very deep water, they are practically impossible to repair. Quality is therefore a crucial requirement, and the customer and the manufacturer must have total confidence in the manufacturing process.

Umbilicals supply the electrical and hydraulic power required by the control functions of the wellhead, subsea

Tube production

Library of qualified welding procedures

The process begins with the super-duplex tubing.

A first method consists of joining tubes at least 12m in length and with an inside diameter ranging from 25.4 to 88.9mm (1" to 3½"). Following tube end preparation in the workshop, the tubes are butt welded to form a several-thousand-metre- long pipe coiled on an enormous spool. To tackle this job, Polysoude proposes its MU range of open-head orbital TIG welding equipment with arc voltage control (AVC) and torch oscillation control (OSC) to produce a flawless weld seam over the entire thickness. This head is generally combined with a P6-type power source and a wire feeder. A PC 300 power source can be selected for particularly demanding applications in terms of quality and productivity.

It must be emphasised that only the TIG (GTAW) process can guarantee the integrity of the material by controlling the energy input rate. The high level of flexibility of the TIG process lies in the fact that filler wire speed is independent of the welding current. Obviously qualification of the welding procedure must meet quality requirements relating to the weld and continuity in the mechanical and physical

Spool of butt-welded umbilical cable tubing

Quality assurance with parameter monitoring and storage

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Tube ProducTs INTerNaTIoNal November 2015

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