The UK P&I Club presents a case where a defective lube oil cooler caused pollution. Namely as the ship was alongside, oil sheens were observed floating on the dock water around the stern, which were believed to be from lubricating oil leaking from the stern tube seal.
The incident
As a vessel was alongside, oil sheens were noticed floating on the dock water around the stern. The source was suspected to be lubricating oil leaking from the stern tube seal.
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After mitigation and clean up measures, arrangements were carried out to dry dock the ship and effect necessary repairs. After inspection, pieces of fishing net were fouling the propeller shaft in way of the stern tube seal.
After renewing the seal, the vessel was re-floated and returned to service. A week later when at anchor, oil sheens were again seen around the vessel’s stern upon which the master informing the local authorities and arrangements made for cleaning up the pollution.
As it was believed the oil was again leaking from the stern tube, the vessel went to a nearby shipyard to investigate the problem. More inspection of the stern tube seals did not detect any deficiency or oil leaks but after re-floating and shifting to a lay-by berth, oil sheens were again seen around the vessel’s stern above the main engine lube oil cooler overboard discharge.
A diving inspection confirmed the presence of oil in the discharge water when the lube oil cooling water pump was operating.
Analysis
The main engine lube oil cooler was leaking at the sea water outlet flange and collected water indicated signs of oil contamination.
The owners arranged for the cooler to be repaired which involved the renewal of sealing gaskets and a number of heat exchanger plates and after reassembly, the unit was successfully hydraulically tested.
According to the UK Club, the management assumed the second oil leak came from the stern tube, but with hindsight, all other possibilities for the leakage of oil should have been investigated.
The deficient condition of the lube oil cooler caused not only a pollution incident, but also significant costs regarding clean up, inspections, repairs and off-hire.
Lessons Learned
- Machinery relating to oil systems must be properly maintained according with the manufacturer’s instructions;
- The condition of overboard discharges should be closely monitored;
- Closely monitor LO system storage tank levels for any unusual consumption;
- When oil release from a ship is observed or suspected, respond in accordance with the vessel SOPEP;
- Report any pollution to the proper authorities, inform the Club, take samples and make sure that all possible reasons for leakage are considered and eliminated;
- Poor machinery maintenance can risk the environment and be very expensive.
