gg.pdf - QUESTION 3 PAGE 7 A crack has been discovered in...

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QUESTION 3 PAGE 7 A crack has been discovered in the lower section of a bedplate transverse girder; (a) State with reasons why such a crack could occur. (4) (b) Explain the procedure to be adopted under these circumstances. (8) (c) Explain how future incidents may be minimised. (4) a) Possible reasons for a crack appearing would be 1 Excess load on the transverse girder from High combustion loads due to excessive power output from that cylinder Misalignment of the bedplate 2 Incorrect tension of the tie bolts for a slow speed engine 3 Manufacturing defect b) Due to the position of the crack in a highly stressed area of the engine structure, investigation into the extent of the damage would be required and prevention measures implemented to limit crack growth. Checks would be made of the crankshaft deflections and tie rod tension to ensure that these are correct/acceptable. To investigate the crack, the area around it would be exposed, which could include light grinding to remove the protective paint covering. The best NDT method on-board would be used to find the extent of the crack, and methods such as dye penetrant or magnetic particle investigation (MPI) could be used. Once the extent of the crack is established, then advise would be sought from the engine makers to ensure that the engine is safe to operate. To reduce the loads present in the bedplate, the engine power for those cylinders would be removed by lifting the two fuel pumps. This would be a prudent course of action until the extent of the crack had been fully identified. Class would be informed, especially if repairs are to be actioned, to ensure that any proposed method of repair would be acceptable to them. c) Future incidents would be minimised by preventing the causes stated in part a). Regular checks would be made on the cylinder powers developed by taking indicator cards, and on the crankshaft alignment by taking deflections. Tie bolt tension would be checked every 12 months. Also crankcase inspections would ensure that visual inspections beneath the bedplate are carried out at every inspection.
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