Metalock Engineering, which specializes in on-site machining, saved the day for Statoil when it repaired a damaged part in the turret system of the Norne FPSO without production having to be interrupted.
The Gothenburg-based company was called to the ship in the Norwegian Sea when bearing pads came loose in bad weather, causing extensive scratches to the 22 m-diameter bearing surface of the turret. Statoil was concerned that the damage might be bad enough to cause the surface to gall, leading to total breakdown in the system, recalls Ronny Asp, senior supervisor for Metalock's on-site machining division.
Inspection showed that 1 mm had to be machined off around the total diameter of the bearing surface, both axially and radially, and then the machined area had to be polished. Statoil further specified that the work should be done while full production continued, and that no sparks should be caused, as the bearing section is in an area of high explosion risk.
Milling machine performing repair of derrick rails on Sleipner A platform.
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Metalock developed the necessary tools, including two machine holders, one acting in the vertical plane and one in the horizontal. The bearing surface was machined in sectors of 7° at a time, each one first milled and then polished. When one sector was finished, the ship was turned to make the next sector available. Water was sprayed on during the operations to prevent any sparks.
Statoil has since commissioned the company to perform similar work on the Åsgard A production ship. In this case a 110° sector was repaired.
Snorre realignment
Metalock has also worked on other Statoil installations. Last year, for instance, it was called out to the Snorre A tension-leg platform by maintenance contractor ABB when a generator shaft was out of alignment. Repair work involved remachining part of the shaft to a tolerance of ±0.008 mm. In this case Metalock developed a machining tool that rotated around the shaft.
Similar rotating machinery was used when the company machined the surface of a gasket in a heat exchanger on Statoil's Statfjord C platform. It also repaired two 8-m rails which form part of the derrick support on the Sleipner A platform. In this case up to 12 mm had to be removed to a tolerance of less than ±1 mm.
For more information contact Ronny Asp, Metalock Engineering. Tel: +46 31 707 1331, fax +46 31 707 1313. [email protected], www.metalock.org
