AIR COOLER RETUBING
In one of the bulk carriers, after 2 days of sailing, the ME speed started slowing down, and ultimately, the engine could not be run. When started, black smoke started coming out and engine stops. The ship was in Indian Ocean, and it was towed to the nearest anchorage at Sychelles.The ER team started decarbonising the units, all units were decarbonised, the units were very dirty, but all the piston rings and the liner conditions, piston conditions were good.
Fuel injector tested and boxedback. Turbo charger overhauled and boxed back. Air cooler opened up and found on the SW side, some dirt, same cleaned and also air side top surface was found slightly dirty. The reason could not be analysed, and it was decided to check the condition of the fins of the air cooler as this was the only thing left to be checked. The air cooler was taken out and on inspection found the bottom side there was too much enlargement of the fins and the top side the fins were of normal size. The enlarged side at the bottom was actually blocking the passage for air to the engine.The air cooler was kept outside, the casing boxed back, SW lines blanked, the engine was started and found starting satisfactorily.
The speed could be picked upto normal rpm with the scavenge temperature going upto 70°C. Now the reason had been narrowed down, the company was requested to send in a new air cooler.The manufacturer of the air cooler was contacted, and he was of the opinion that if aluminium is used for fins as material with brass for tubes, then in case of SW leakage, the aluminium will become aluminium chloride, which will expand enormously blocking the bending other fins. Hence he suggested that even though the job is going to be handled by some local workshop, while retubing, it is better to consult the manufacturer for proper material details.Lessons Learnt: always consult the manufacturer or refer the manual for material specification while repairing or reconditioning.