Answer EKG Question 6

Q6. Describe the importance of maintaining the quality of lube oil in maintaining the proper health of marine diesel engines highlighting the role of

(a) Automatic back flushing filters.

(b) Lube oil separators

(c) Magnetic filters

(d) Visual Inspection

(e) Periodic laboratory tests.

Answer: Lube oil health

Functions of a Lubricant:

• The primary function of a lubricant is to prevent friction by creating a boundary layer between two surfaces
• Dissipate heat from surfaces
• Transport contaminants to filters
• Protects from oxidization and corrosion
• Power transmission

The properties of lubricating oil need to be maintained within the specified parameters, in order to the engine to operate smoothly and efficiently. following properties of lubricating oil are desirable:

• Viscosity
• Pour Point
• high Flash point
• high Oxidation stability
• low Carbon residues: To be low
• Total acid number  or TAN
• Total basic number or TBN
• Detergency
• Dispersancy

Effects upon failure to maintaining the quality of lube oil:

1. If very low quality of system lube oil is maintained in circulation ,function of lubrication will be disturbed.
2. Less amount of lube oil in circulation causes rise in temperature thus reducing the viscosity leading the failure of boundary lubrication due to decrease in oil film thickness.
3. Insufficient time for de-aeration and it accelerates the process of oxidation of oil .Due to oxidation Lubrication oil properties are lost Forms sludge and high temperature sludge adhere to metal surface. Formation of acids/corrosive attack. Increase the viscosity of oil.
4. Increase in friction ,wear,heat corrosion,contamination and noise and it reduces the engine performance to critical and in extreme cases engine may seize.
5. Additives will deteriorate faster results in loosing properties like detergency and depersency .

 (A) Role of  Automatic back flushing filters:

Continuous back-flushing ensures constant pressure and long intervals between inspections. auto back wash filter offers considerable man-hour savings due to their high level of reliability and the fact that they require virtually no supervision.

A Controller keeps monitoring the differential pressure across the filter. The backwash cycle starts when the differential pressure reaches at a pre-selected level. Once the backwash process gets completed, the controller resets automatically, and the whole process starts again when differential pressure rise again.

 

(B) Role of lube oil saparator:- 
Lub oil separators which work as purifiers are very essential in maintaining the crank case oil of slow speed engines as well as large medium speed diesel engines water free and this has to be a continuous process , even continued when engines are idle. Apart from removing the water the purifiers also remove the sludge that is generated especially if the system is operating on a medium speed engine. Water finds its way from various sources and they are:

• Condensation of vapour from the atmosphere stagnant in the lube oil sump.
• Occasional leaks from lub oil coolers especially due to cooling water on with leaking water valves when the engines are idle.
• Leakage of water from liners which are unnoticed.
• Improper purification resulting in water remaining in the oil, till it is discovered.
• Leakage of heating steam in sumps and heaters for the purifier.
• Continuous operation of the purifier even during idle time of the engines is necessary to prevent bacterial degradation

(C) role of Magnetic filters:- They are often used in lubricating oil systems, where a large permanent magnet collects any ferrous particles which are circulating in the system. The magnet is surrounded by a cage or basket to simplify cleaning. Magnetic filters play a very important role in filtering ferrous debris collected in the oil as abrasion particles of the liner or piston rings especially in medium speed engines In crank case oils it may be the grit from crank pins and journals which cause wear of these components.

It is an indicative device of detecting a faulty bearing when conducting a crank case examination.

(d) Role of Visual Inspection:-Aim of inspection and test of lube oil is to monitor deterioration of oil, consumption of oil, wear of machinery parts being lubricated further use or rejection of lube oil. monitoring of lube oil condition is a indirect indication of the health of machinery.

Many basic lubrication problems can be found just by simple visual inspections such as level, pressure, temperature, colour and odor  monitoring of the lube oil.

additionally following tests can be carried out on board.

  

alkalinity test:- a drop of methyl orange and phynopthaline  solution on blotting paper followed by a drop of sample oil at the center if previous drop. colour change arround the oil spot can be compared for the results

• red colour is indication of acid 
• blue/green colour is an indication if alkalinity
• yellow colour indicates neutral

Water Crackle test:- this method is to determine water presence in the lube oil where the oil sample drops are heated in an aluminium container over a flame. If water is present crackling sound will come.

Spot test:- In this test a drop of lube oil is put on the blotter paper and it is then dried for few hours.

•  irregular shape of spot indicates presence of water.
• uniform distribution of contaminants indicates good dispersiveness.
• contaminants concentrated at center indicates the poor dispersiveness.
• black colour of the spot indicates heavy contamination.

Odor of oil test:- Rotten egg smells is an indication of microbial degradation of oil , also sliminess of the oil in the crankcase painted surfaces can be observed, additional problems may be observed like increased acidity and water content, filter choking more frequently poor heat exchanger performance, black staining of white metal bearings and corrosion of exposed steel surfaces.

Viscosity Test:- This test is performed by using a Flow stick in which two paths are provided for flow of oil side by side. In one path fresh oil is filled and in other side path used sample oil is filled. Now the flow stick is tilted allowing oil on both paths flowing in the direction of the tilt due to gravity. A finish point is provided along with reference points along the flow stick and the position of used oil is checked when fresh oil reaches the finish point. 

• reduced viscosity indicates dilution with distillate fuel
• increased viscosity indicates contamination with heavy oil, carbon or oxidation of oil.

(e) Role of Periodic laboratory tests:

Laboratory test of lube oil is helpful in knowing the fluid properties, contamination and wear debris.

Various test like Foaming characteristics, water separability, air release value, rust prevention characteristics, oxidation stability, flash point, corrosion test, particle sizing and counting, TAN, Moisture, viscosity measurements etc are carried out by shore based laboratory. 

Typically, an oil analysis report comes with a written summary section that attempts to put the results and recommendations in layman’s terms. But, since the laboratory has never seen the machine or know its full history, these recommended actions are generic and not tailored to your individual circumstances. Therefore, it is the responsibility of the personnel who receive the lab report to take the proper action based on all known facts about the machine, the environment and recent lubrication tasks performed.