The Swedish Club has published some lessons learnt from a machinery failure. The six cylinder, medium speed type engine sustained serious damage serious damage and had to be renewed. Additionally, the turbo charger had to be overhauled.
The vessel in question was in ballast and at anchor, waiting for further instructions. After seven days the weather got worse and the ship’s anchor dragged. The anchor was heaved up and the vessel started to slow steam in the area.
After about a day, the differential pressure alarm of the main engine duplex lubrication oil filter sounded in the engine control room. The crew found aluminium and other metal inside the lubrication filter, and in the crankcase of the main engine, metal particles were found.
The investigation that followed showed that the metal parts found in the lubrication oil filters emanated from piston rings and piston skirts. Three pistons had almost seized. The main engine, a six cylinder medium speed type, had serious damage and the following parts had to be renewed; namely, all cylinder liners, three complete pistons, piston rings on all cylinders, all main and connecting rod bearings.
Moreover, the turbo charger had to be overhauled as the nozzle ring had broken. The complete lubrication system had to be carefully cleaned and flushed. The vessel had to be off hire for about two weeks.
In addition, the pistons in cylinder units numbers 1 and 3 were melted down in certain areas and the skirt in number 4 was torn. Liners were also scuffed. The cylinder lubrication channels were clogged and so cylinder lubrication had been inactive. The lubrication oil pump had deteriorated because of the hard impurities in the lube oil system.
Probable cause
According to the Swedish Club, the engine had been operated on a high thermal load for a long time and the turbocharger efficiency had been affected by fouling. The lubrication oil had actually been contaminated for some time.
There had also been indications that something had gone wrong. Specifically, it was written in the log book that the auto filter had been shooting up to 609 times a day, but the engineers had not been concerned.
Lessons learned
Some of the lessons learned from this incident are:
– Fuel oil samples before and after purifiers were taken and analysed. The result indicated that the purifiers were working satisfactory. All fuel oil analyses from bunkering were within specification;
– Several samples of the damaged piston rings were sent to a laboratory. The conclusion was that the excessive wear of liners and pistons was not caused by catalytic fines;
– The cylinder liner lubrication system was tested and was found to work properly;
– At the time of the casualty the main engine, including turbo charger, had been running 7,300 hours since its previous major overhaul. This overhaul had been carried out 18 months previously;
– Investigation of the maintenance records showed that maintenance had been carried out in accordance with manufacturer’s instructions;
– When reviewing the monthly main engine reports it became obvious that the main engine exhaust temperatures of all cylinder units had increased 30°C – 40°C for the previous six months;
– The turbo charger revolutions had dropped from about 14,500 rpm to 12,000 rpm at 85% load as had the charge air pressure from 1.7 bar to 1.2 bar. These changes also began to appear in the past six months;
– Due to high exhaust gas temperatures, the engine was under a high thermal load, which finally caused it to breakdown.
The company has taken the following actions:
– The follow up of all engine logs has now been improved, especially the understanding of the exhaust gas temperatures and their alarm levels;
– The scope of performance reporting between vessel and office will also be intensified in the future;
The trend logging of reported performance parameters in the shore manager’s engine performance monitoring system has been implemented;
– Engineers will be sent on four stroke engine training courses.
