The problem arose when the swivel and jacket legs for the platform were found to have been fabricated to incorrect dimensions, and would not fit inside each other. Rather than refabricate the whole structure (which would take considerable time) Furmanite, the specialist technical and engineering services company well known for its on-site machining expertise, was called in.

Furmanite’s solution was to machine the bore of the swivel jacket and outside of the swivel leg on site. This involved removing up to 6mm from the bore, 400mm in from each end of the four pipes (each measuring 1.4 metres diameter, 3.5 metres long and 75mm thick). This would enable a fabricated sleeve to be fitted and welded in, and the sleeve machined to size to accept the swivel leg.

The work had to be completed within a tight time window so as not to delay rig construction (which would have incurred financial penalties for the construction company customer), and had to be within critical 3-4mm tolerances.

Each swivel leg needed to rotate within its jacket, but the fabrications were different sizes, so each of the four pairs required different machining dimensions. Additional challenges included the fact that the bores of the swivel jackets were out of round, so that setting up of the boring bar took time to ensure best fit and minimise machining.

Having identified the requirement, Furmanite Malaysia developed customised machines to meet the demands of the project. The work was undertaken using a six inch boring bar, with fabricated legs mounted on the outside of each swivel jacket to hold the bearing housings for the boring bar. Additionally a 60 inch pipe cutter was adapted to machine the shims or sleeves fitted around the outside of the swivel legs using a lateral slide, so that each would rotate within the jacket.

“We were able to complete the work on site in considerably less time than would have been required to refabricate the whole structure. The customer was delighted with the solution,” Furmanite Malaysia operations manager Chris Lord commented.

“Our services are often called upon for operational maintenance projects but many of them, such as on-site machining, are equally valuable at construction stage,” he added. “Where components are manufactured separately off-site and brought together on site for construction they often do not offer the precise dimensions, alignment or surface finish for a perfect fit. On-site machining can rectify this efficiently and cost-effectively.”

Other instances in which Furmanite’s on-site machining expertise has proved valuable on new rig constructions have included milling pump and compressor bases to rectify distortion caused by welding to the platform deck; drilling into superduplex pipework for additional welded fittings where a design change had required additional connections; and milling of drilling derrick topside skid rails in-situ when they were found to be twisted across the face after installation.

Furmanite has the capability to undertake on-site machining projects from plant maintenance requirements to large scale new-build turnkey packages. Applications range from circular structures up to 30 metres diameter, to requirements such as line boring and pipe cutting, achieving workshop tolerances in the most demanding environments. Flange facing, milling, boring, drilling, journal turning, pipe cutting, weld preparation and valve seat lapping are all undertaken using a range of standard and special application portable tools.

Sarah Manwaring-White, Keep in Touch Ltd,
Tel: +44 (0)1451 844 488
Email: sarah_mw@keepintouch.co.uk