Incident Information on Contamination of Main Engine Lubrication Oil by Seawater

This incident refers to the contamination of a ship’s main engine by seawater. The engine room bilges became flooded due to a leaking sea water pipe. Proper actions were not taken when the alarm sounded, so the leakage was first discovered when water had reached the engine room floor plates. Consequently, the leakage was stopped, bilges emptied and the ship resumed its voyage. Shortly after resuming the voyage, the main engine stopped due to low lubrication oil pressure.

The lubrication oil was analysed and contamination with seawater was identified. The engine was not re-started before the sump tank was cleaned and new lubrication oil added, because possible damage to engine bearings was considered as a potential consequence. This resulted in the vessel drifting for approximately 24 hours.

The lubrication oil was heavily contaminated with sea water, and could not be cleaned up by the separator within reasonable time to continue the voyage. The lubrication oil was therefore replaced. Extent of damage to the main engine bearings was not known. Main engine rubber diaphragm positions (red circles) are showed above.

During bilge flooding, sea water had entered into the lubrication oil sump tank through a cracked rubber diaphragm. Main engine rubber diaphragm positions (red circles) are showed above. The rubber diaphragm is the flexible connection between the engine crankcase and the lubrication oil sump tank in the hull. One purpose of having it is to prevent contamination from entering the sump tank from the engine room. A rubber diaphragm may crack due to the long term exposure to forces from the movement of the engine relative to the hull.

This incident highlights the following lessons to be learned:

• Rubber diaphragms are very important for keeping the lubrication oil system intact, and should get sufficient focus by the engine room crew at times when available for inspection, by example when the lubrication oil sump tank is subject to cleaning.
• If the engine room should become flooded, lubrication oil for the engine is to be checked for contamination. If found contaminated, the rubber diaphragms are to be checked for cracks and the lubrication oil system is to be handled as necessary in order to resume acceptable lubrication oil quality.
• Watch keepers should be proactive and investigate the cause of every alarm in the engine room.

Source: DNV