Lub oil is blood of the machinery; most valuable, so it requires utmost care. This is the only fluid in the machinery which needs to be supplied before starting without fail, rest all fluid, water, fuel etc, can be supplied once machinery started. Common problem of lub oil is contamination, it can be water, fuel, metal particle or in some cases some unexpected foreign particles.
Engine system oil- Usually oil remains in good condition if there is no contamination of water, fuel or foreign particle. Sea water or fresh water ingress from lub oil cooler is most common problem, in plate type cooler it can be through cooler gasket or sometimes through pin holes in cooler plates, nevertheless not rare. Pin holes are difficult to identify by naked eyes, it can be identified by ultrasonic measurement. In case plates are old or material is poor, this reason should not be ignored, and old plates must be inspected by ultrasonic. Other option is to replace plates if they are old, now a days, due to many OEM’s in the market, plates are no more expensive. In tube type cooler, which is very rare now a days, tube leak is most common source of water ingress into lub oil, the reason is again failure of tubes due to poor quality or material erosion.
Care of lubricating oil cooler – Onboard cleaning should be avoided as far as possible. Best practice is to carry out in place chemical cleaning or backwashing, replace gaskets after every cleaning and use professional company or experienced crew to assemble cooler. Before putting the cooler in use, it has to be pressure tested.
Main engine sump and bedplate are separated by a rubber diaphragm fitted between them, this diaphragm takes care of movement between bedplate and sump. This rubber diaphragm gets brittle and leaks over a period of time. It is prudent to replace the diaphragm every 10 years. Some times water is accumulated on the tank top and engine pit, if this diaphragm is old and cracked, water will find its way to sump.
Water can pass through from tank top to engine pit, once engine pit is filled, it will enter to sump via damaged diaphragm. Diaphragm location is shown here.
MAN Engine – There is seal between fuel pump and camcase, very common now a days to have leakage through plunger and barrel due to reduced viscosity of Low Sulphur Marine Gas Oil and Low sulphur fuel oil, fuel leaked off through plunger and barrel usually drains through fuel pump casing drain. The drain to be checked and cleared regularly. There is sight glass fitted on the base of the fuel pump, it has to be kept cleaned and inspected every watch. the seal between pump chamber and camcase to be renewed whenever fuel pump is overhauled
Drawing showing seal between fuel pump and camcase; source – MAN manual.
Lub oil filter failure – Improper maintenance of filter, poor assembly of it or old and damaged filters contribute to lub oil contamination.
Auxiliary engine – Medium speed engines are more prone to damage if system lub oil is poor. Common source of water contamination are; cylinder liner leak, cooling water pump seal leak, lub oil cooler leak, cylinder cover crack etc. Routine maintenance of cooling water pump, lub oil cooler, liner seal ring renewal during overhaul and finally regular crankcase inspection is key for preventing major breakdown due to water ingress. Other source of lub oil contamination is blow past; high liner wear and unbalanced units will cause blow past into the crankcase and cause high carbon content. Third major contaminant is fuel oil, this is caused due to leaky fuel pump and choked drain lines. It is prudent to keep the fuel pump channel clean and if pumps are leaking then replace or overhaul it.
Hydraulic system oil – this grade of oil needs highest standard of purity. Filters in hydraulic systems are one of the finest filters because of high pressure in the system and very fine (in micron) clearances. Hydraulic oil is used mainly in crane, mooring winch, windlass and steering gear system, here impurities are in the form of contamination and high Particle counts. On weather deck equipment, it is usual to have some water ingress in the hydraulic system through storage tank sounding pipe or breather pipe. Winch cover plates, if not properly tightened would alow water ingress into gear case. As per Viswa Lab reports 60% of the hydraulic oil samples received for routine lubricant condition monitoring suffers very high particle counts (or) contamination. Wear and tear of running part is another source of contamination, besides that rust and dirt in the system also caused contamination.
Care of hydraulic system oil – drain off condensate, keep the filters clean, magnetic filter to be used to prevent metal wear and tear going in to the system, proper maintenance of sounding and breather pipe are most common preventive maintenance on hydraulic system oil. Keeping storage tank and new oil clean is another key factor.
Metal particle in lubricating oil – this is after effect of contaminated lub oil. In some cases ,material failure of bearing or running gear is also a source of metal particle in lub oil.
Fresh lub oil – In general, keeping the storage tank clean and sounding pipe and vents secured are applicable for all grade of lub oil. In some cases water ingress has been found in the storage tanks through side water tanks or sounding pipes or vents. Regular draining of even freshly stored tank is also recommended to identify if these is any water ingress.