Failure analysis of a leak-off oil pipe from injection valves of an off-shore operating diesel engine

The failure analysis of a four-stroke 3000 kW off-shore operating diesel engine is presented. The failure occurred during engine normal operation period in the leak-off oil pipe from the injection valves, which experienced a fracture through the pipe wall and a diesel engine fire as a result. A detailed analysis of all elements which had an influence on the failure initiation was carried out, namely leak-off oil pipe vibration level, pipe stress level, presence of corrosion pits on the pipe external surface under the zinc coating and engine components temperature distribution in the failure zone. It was found that the crack initiation and propagation of the leak-off oil pipe from injection valves was driven by a fatigue mechanism, which was facilitated by loose pipe supports (excessive pipe vibration) and corrosion pits on the pipe surface that acted as stress concentrators. The contact of leak-off atomized oil due to the pipe through wall fracture with the hot engine exhaust muff (390 °C approximately) caused local fire of the diesel engine.