Preventing auxiliary engine overspeed

Auxiliary engine overspeed incidents can lead to substantial financial repercussions. The average repair expenses in examined cases amounted to around USD 250,000, encompassing repairs, spare parts, specialized labor, and ancillary services. Additionally, the economic loss from operational downtime may surpass the repair costs. Repair durations in the cases analyzed ranged from 22 to 90 days, primarily influenced by the magnitude of damage, spare part availability, and warranty terms. These delays can significantly disrupt vessel operations and commercial timetables.

Key insights from these claims indicate that the mechanical stop transmission often proves to be a weak point. In two instances, shutdown signals and overspeed alarms were triggered, yet mechanical linkage failures impeded the fuel rack from reaching the zero position. The engines persisted in operation until crews manually cut off the fuel supply.

Both episodes resulted in severe engine damage, encompassing bearings, valve gear, and crankshaft components. Routine torque assessments of clamps, examinations of pins and flexible links, and blue paste contact assessments could have averted these failures.

Another incident involved the installation of a new actuator with an incorrect rotation setting, neither the service engineers nor the crew verifying the rotation direction and safety functions prior to engine start-up. This led to immediate overspeed and substantial damage. Initially, the cause was suspected to be a stuck index arm, but testing and dismantling of the governor revealed no defects. Subsequently, the service provider acknowledged that the incorrect actuator setting was the root cause.

In a separate case, extensive damage occurred due to the resilient gearwheel connected to the flywheel and tuning wheel, necessitating reaming damaged bolt holes, manufacturing oversized bolts onboard, and realigning the generator. The investigation uncovered that damaged speed pickups had come into contact with the flywheel, causing the engine to lose its speed signal.

Consequently, the overspeed protection system was unable to initiate a shutdown, and the emergency stop valve failed due to deteriorated O-rings immobilizing its internal components. This prevented the control air from positioning the fuel rack to the zero-fuel setting. A final case saw the crew discover severe roto-cap damage only months after an overhaul, necessitating the replacement of all cylinder units, rods, and pistons during a 22-day repair period.

The critical takeaway is to ensure piston crowns, governors, actuators, and linkage kits are compatible with the specific engine model before installation and to test the entire safety system before returning the engine to service. To mitigate risks and costs, it is advised to conduct a local emergency stop function test after any control, fuel, governor, or actuator work.

Additionally, applying air to the stop cylinder and visually confirming the fuel rack reaches the zero position upon every pump is recommended. Performing weekly visual checks and monthly torque/contact verifications of linkage integrity, along with monthly tests observing the rack being drawn to zero, are also recommended. Maintaining detailed logs of torque values, blue-paste photos, rotation alignment images, overspeed test sheets, and hardness/runout results is essential.