021/15 Need for Planned Maintenance Schedules on Critical Equipment

Lessons from UK MAIB’s Marine Accident Reports

The UK MAIB has recently issued the first Safety Digest for this year which includes lessons learnt from maritime accidents. One case refers to over-speed damage and highlights how important planned maintenance schedules on critical equipment are.

Over Speed Damage
Following a main engine overhaul on board a dredger, the engine was started for a trial run. After the initial start, the engine’s speed gradually increased over its normal operating limit. None of the over-speed protection devices, or the operation of the mechanical emergency stop, stopped the engine, which was eventually shut down by covering its air intakes and starving the engine of air. No secondary damage was apparent but two defects, which could have contributed to the over speeding of the engine and the failure to shut down the engine, were rectified. The engine was then tested but the test run did not include the operation of the engine’s protection devices.

A few weeks later, the dredger was stopped while on passage to enable a fractured high pressure fuel line on its main engine to be repaired. Once the repair had been completed, the engine was re-started, but its speed again quickly increased beyond normal operating limits. All of the methods intended to stop the engine in the event of an over-speed, including the manually operated stop lever, failed and the engine suffered a catastrophic failure.

Subsequent investigation identified:

• Routine testing of the over-speed trip mechanism had not been carried out in accordance with the planned maintenance system because the engine tachometer was faulty and did not provide an accurate measurement of the engine’s speed.

• The over-speed trip assembly bracket had broken away from its mountings, which prevented the trip from operating as designed.

• The engine’s governor contained insufficient oil to enable it to operate correctly. The governor oil had leaked over a period of time from a loose pipe fitting.

Lessons Learned

Thorough and regular rounds should be carried out for all running machinery, including checks on the security of fixtures and fittings. Without such checks the opportunity to identify equipment failure or malfunction at an early stage could be missed. A few loose bolts can easily result in a catastrophic failure.

During test runs following maintenance or fault rectification on control systems, a comprehensive testing and trials programmed should be followed to verify the correct operation of the safety devices. Failure to do so is only asking for trouble.

Planned maintenance schedules on critical equipment must be followed at all times. Planned maintenance tasks for critical equipment should not be “closed” if they are unable to be completed. Such tasks should remain “open” or “deferred” but they must be completed as soon as is practicable and not just left until the maintenance becomes due again. In this case, the continual deferral of the testing of the over-speed trip proved to be very costly.

Source: UK MAIB

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Thank you & Best Regards,

Eng. Dimitrios Nikolaos Spanos
Lead Maritime Auditor / Principal Surveyor
Member of IRCA, IIMS, ELINT, HELMEPA & Nautical Institute

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