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Case 4
Fire in Engine Room of Container Ship

Narrative

On 24 August 1998, the 50,350 gt container ship Repulse Bay was on passage from Rotterdam to Port Said. At 1902 alarms sounded indicating low air pressure on the main engine’s exhaust valve springs and a fire in the engine room. At the same time the main engine slowed down automatically.

An investigation found several small fires on the main engine’s exhaust manifold and oil spraying on to it from a broken pipe on No 7 unit. The engineers stopped the main engine and lubricating oil pumps, and promptly tackled the fires with foam fire extinguishers. They were successful.

Bolts securing the exhaust valve actuator housing to the cylinder head were found to have fractured enabling it to move freely. This caused the attached oil pipe to fail and oil to impinge on a small unlagged area of the exhaust manifold around welded support brackets and ignite.

After replacing the exhaust valve, actuator securing bolts and the oil pipe, the remaining spilt oil was cleaned up. The main engine was then restarted and Repulse Bay resumed her passage.

The Lessons

Failure of any component on a diesel engine has the potential to cause significant damage.

Although regarded as ‘static’ items, the securing bolts on this exhaust valve actuator were subjected to cyclic loads and were therefore working under conditions where fatigue could become a problem.

Metallurgical tests showed that these bolts had failed due to fatigue. Some of the precautions which can be taken to reduce this type of failure are:

1. An engine manufacturer may specify the material, method of manufacture and working life of critical bolts and studs. If so, it is important to use specified components and ensure they are renewed when specified working life is expired.

2. The pre-loading of bolts, studs etc has a significant effect on the level of stress induced in service. Too low a pre-load is as likely to promote fatigue failure as too high. If a manufacturer recommends a pre-loading specification, its guidance should be followed.

3. Wear of damage to threads, even if apparently minor, can generate stress concentrations that will, in turn, reduce a component's resistance to fatigue.

4. Where the manufacturer makes no recommendations, or none are available, there are some easily visible features which should disqualify bolts and studs being fitted to critical engine assemblies. These are: rough surface finish, corrosion, sharp internal corners, worn or damaged threads, sign of fretting from previous service and distortion such as bending. Some of these features are also applicable to mating threaded components such as nuts.