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Metalock’s attention to detail rescues auxiliary gearbox for shell north cormorant

On the face of it replacing a bearing on an auxiliary gearbox used to drive a lubricating oil pump on a turbine driven gas compressor is not a difficult task but the engineering team on Shell U.K. Exploration and Production’s (Shell Expro) North Cormorant platform in the northern North Sea experienced two problems.

North Cormorant, operated by Shell Expro, approximately 175km (109 miles) north east of Lerwick, Shetland.

Gearbox failures and in-situ machining

The gearbox had failed on two or three occasions in a short time due to a bearing spinning in its housing and the Shell engineers decided that the best solution was to bore out the housing, insert a sleeve and a new bearing with the necessary interference fits. But the gearbox could not be removed which meant that boring, re-sleeving and alignment had to be done in-situ.

"They knew that alignment was critical to the efficient operation of the gearbox and confirmation of their on-site measurements using an identical gearbox onshore illustrated their professional approach"

Metalock engineers evaluated what was required, took the measurements they needed enabling them to purpose design a boring bar arrangement complete with supports. To ensure accuracy of their figures they also visited Alstom Power in Aberdeen where there was an identical gearbox. Satisfied that their tooling could set up to accurately in-line bore the housing to the tight tolerances required, Metalock began the task. Following the boring, a sleeve and new bearing were fitted. The pump was then reassembled.

Commenting on the Metalock operation Stan Wood, contract maintenance engineer for Shell Expro on North Cormorant was full of praise for the attention to detail paid by Metalock engineers in carrying out their ‘rescue’. “They knew that alignment was critical to the efficient operation of the gearbox and confirmation of their on-site measurements using an identical gearbox onshore illustrated their professional approach”, he added. The pump has now been running for over six months without problems.