Marine Engineering Study Materials

Contamination of Lubricating Oil by Water

Causes

1. Leakages from cylinder cooling water system.
2. Leakages from piston cooling water system (for water cooled pistons).
3. LO cooler water leakages (can be seawater or freshwater).
4. Leakages from sump tank heating coils.
5. Condensation of water vapour inside crankcase.

Effects

1. Acid formation in lube oil for trunk type piston engines.
2. Reduction in cooling efficiency.
3. Reduction in load carrying capacity of lube oil.
4. Reduction in lube oil properties such as TBN.
5. Formation of sludge.
6. Corrosion in various parts of the machinery.
7. Microbial degradation of lube oil.

Remedies

1. Proper purification of lube oil with minimum throughput.
2. Renewal of lube oil.

How to Deal With Seawater Contamination in Lube Oil

1. Find and rectify source of seawater leakages immediately.
2. Transfer whole sump oil to LO settling tank, maintain temperature around 60 degree Celsius, drain water and sludge periodically.
3. Clean the sump and inspect.
4. Renew sump with fresh lube oil.
5. Run LO purifier in batch operation at about 78 degree Celsius and optimum efficiency, from LO settling tank to tank.
6. Sent purified LO sample for shore analysis.
7. Shore analysis report will specify whether the LO can be reused or treatment such as water washing to be carried out or not.

Procedure for Batch Purification for Lube Oil

Batch purification of lube oil is carried out when,

• Water leaks into lube oil
• LO is mixed with high insoluble combustion products
• LO sump tank is cleaned and refilled with LO

The procedure for batch purification of LO is given below:

1. Whole LO is transferred from LO sump to settling tank through LO purifier or LO transfer pump.
2. Allow LO to settle for about 24 hrs at around 60 degree Celsius.
3. Drain sludge and water periodically from the tank.
4. Clean the sump thoroughly and examine.
5. Purify oil at optimum efficiency, proper temperature and minimum throughput. Sent the purified oil to the sump tank.

Allowable Limits for Water in Lube Oil

• For cross head type engines water in LO to be less than 0.2%; take immediate action when the water content is between 0.5% to 1.0%; water content above this may damage the engine.
• For trunk type engines water in LO to be less than 0.1%; take immediate action when the water content is above 0.5% ; water content above this may damage the engine.

See Also: Oil Carry Over in Air Compressors

See Also: Main Engine Lube Oil Cooler Fouling