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Functions and Properties of Lubricating oil on Ships

Functions and Properties of Lubricating oil on Ships

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What are the functions of a lubricant?

  1. Separate entirely the contact surfaces, thereby reducing static and dynamic friction to least possible value to prevent wear and tear.
  2. Remove heat generated within the bearing.
  3. Protection of the working surfaces against corrosion.
  4. Removal of contaminants.
  5. Dampen noise produced.
  6. Act as a sealant.

What are the Types of Lubrication on Ships?

  • Hydrodynamic Lubrication or Full fluid film lubrication.
  • Boundary Lubrication or Thin film lubrication.
  • Hydrostatic Lubrication or Thick film lubrication.
  • Elasto-hydrodynamic Lubrication or Thin film or square film lubrication.

What are the Properties of crankcase lubricating oil?

  • Viscosity: To be suitable for the purpose
  • Viscosity index: To be high
  • Pour Point: Must be low
  • Flash point: Must be high
  • Oxidation stability: To be high
  • Carbon residues: To be low
  • Total acid number  or TAN: To be suitable for the purpose
  • Total basic number or TBN: To be suitable for the purpose
  • Detergency: For cleaning
  • Dispersancy: To facilitate purification

 What is viscosity?

  • It is a measure of internal resistance to flow between liquid layers.
  • Viscosity of lube oil reduces when temperature rises and vice versa.
  • For engine crankcase lube oil, viscosity is 130 to 240 Redwood No-1 seconds 60°C.
  • For cylinder oil, viscosity is 12.5 – 22 Cst

What is viscosity index?

  • It is the rate of change of viscosity of an oil with respect to change in temperature.
  • An oil with low viscosity index has greater change of viscosity with change in temperature.
  • An oil with high viscosity index has very little change of viscosity with change in temperature, which is a desirable property for lubricating oil.
  • For crankcase oil, viscosity index is 75 to 85.
  • For cylinder oil, viscosity index is 85.
  • Viscosity index of mineral oils is highest, about 115 and this may be raised to about 160 by adding special additives.
  • Hydraulic oils should have high viscosity index for faster response of the system. It is usually around 110.

What is a pour point?

  • It is the lowest temperature below which an oil will stop flow.
  • Pour point indicates that oil is suitable for cold weather or not.
  • Pour point of engine crankcase should be  -18°C.

What is the flash point?

  • It is the lowest temperature at which the oil will give off a sufficient inflammable vapour to produce a momentary flash when a small flame is brought into the surface of the oil.
  • Close flash point for crankcase lubricating oil is around 220°C.

Why flash point is important?

  • Fuel oil flash point is to be high because if it is low, there would be a possibility of fire in storage.
  • Engine crankcase lubricating oil flash point should be as high as possible to prevent crankcase explosion.
  • For safe storage, oil storage tank heating temperature to be limited to at least 14°C lower than flash point to prevent fire.

Average Closed Flash Points

  • Petrol    =  -20°C
  • 70cSt Fuel Oil    =   71°C.
  • Paraffin   =   40°C
  • Lube Oil    =  220°C
  • Diesel Oil  =   65°C

What is Total Acid Number or TAN and Total Base Number or TBN?

  • The ability of an oil to react with a base reagent which indicates the acidity is expressed as TAN.
  • The ability of an oil to react with acidic reagent which indicate the alkalinity is expressed as TBN.
  • The results are expressed in milligrams of potassium hydroxide (KOH) required to neutralise one gram of sample oil for both TAN and TBN.
  • TBN for an oil used for cross head type diesel engine crankcase is 8mg KOH/gram of oil.
  • TBN for an oil used for trunk type engine using heavy oil is 30mg KOH/gram of oil.

What type of engine are using high TBN and why?

If blow pass occur in a trunk type engine using heavy fuel oil, incomplete combustion products reach directly into the crankcase and may cause the contamination of lube oil with acid. Thus in this type of engine to neutralize the acid contamination must be used high TBN oil.

What is detergency and dispersancy ?

  • It is a chemical additive called detergent which has a property of preventing the deposition of carbon deposits and wash away with the lube oil.
  • Dispersant additive is added to divide the larger size deposits into tiny particles to be carried in a colloidal suspension evenly throughout the bulk of oil, which can be removed while filtration of the oil.

Explain the L O sampling procedure to send for LO test ?

  • The sample should be drawn with oil circulation with the system such as a test cock on the discharge side of the LO oil pump.
  • Before taking the sample oil sufficient amount of oil should be drain out to clear the line.
  • The sample is filled into the chemically cleaned container after it is rinsed with the sample oil and immediately closed.
  • The container should be attached with information on engine type, engine running hours, LO running hours, fuel used, draw off point and date of sampling.

Explain Sampling Procedure of lube oil?

  • Draw samples from a connection that comes directly out of the main oil supply line to the engine.
  • Always sample for the same point.
  • Sample only when the oil is up to its operating temperature with the engine running.
  • Depending upon the draw off point, sufficient amount of oil should be drained out of the line prior to drawing the sample.
  • The sample should be filled into a chemically cleaned container after it is rinsed with sample oil and immediately closed.
  • The container should be attached with a label as follows:

 Records for Sample

  1. Date of sample drawn
  2. Point of sample drawn
  3. Type of oil
  4. Type of machinery use
  5. Temperature of sample drawn
  6. The period of time since the last renewal of oils.
  • Avoid sampling from places where the oil may be stagnant or have little or no flow, such as sumps, auxiliary smaller pipelines, purifier suction or discharge lines, drain cocks of filters, coolers etc.
  • Also avoid sampling while engine is stopped.

What is the essential factor effecting the establishment of hydrodynamic lubrication ?

  1. Viscosity of lube oil
  2. Load acting on the bearing
  3. Surface smoothness of moving parts
  4. Speed of rotation
  5. Continuous LO supply
  6. Bearing clearance, bearing length and pin diameter.
  7. There must be convergence between fixed end and moving surface.

Where do locate ME LO sump and its fitting ?

  • It is located under the main engine in the ship double bottom and surrounded by cofferdams.
  • It consist of  1)  level gauge  2)  man holes  3)  air vent pipe  4)  sounding pipes  5)  heating steam coils 6)  suction pipe and  7)  valves for LO p/p and purifier.

Why magnetic fitter is fitted on LO system and where is it fitted ?

  • To prevent pump damage due to ferrous metal particles.
  • Screw p/p used in LO oil system is working in very fine clearance thus to prevent entering the small ferrous particles into the p/p.
  • Magnetic fitter is fitted prior to the main circulation LO p/p.

What are the contaminants in the lube oil ?

  1. Contamination of fresh Water (JW leaking)
  2. Contamination of SW (Cooler leakage)
  3. Contamination of fuel (Poor Atomisation, Unburned Fuel)
  4. Oxidation products (High Exhaust Temperature, Burned Cyl Oil, Carbon from incomplete combustion)
  5. Products of fuel combustion
  6. Foreign mineral matters (Scale formation, Wear and tear)
  7. Biological contamination.

What are the effects of water contamination in lube oil ?

Causes

  1. Condensation of water vapour within the crankcase
  2. Leakage from the cooling water system for cylinder or piston
  3. Leakage from the sump tank heating steam coils.

Effects

  1. Reduce cooling efficiency.
  2. Increase the acid formation in trunk type piston engine.
  3. Can cause corrosion on m/c parts.
  4. Microbial degradation, [Reduce centrifuging efficiency; promote local pitting and corrosion]
  5. Reduce load carrying capacity
  6. Reduce L.O properties, and TBN of oil
  7. Form sludge due to emulsification

 Remedies

  1. Proper purification with minimum throughput
  2. Batch purification if heavy contamination

Maximum Allowable Amount of water in Lube oil?

  • For crosshead type engine , < 0.2 % is satisfactory
  • If water content exceed 0.5 ~ 1.0 %, immediate action should be taken
  • If > 1%, engine can be damaged
  • For trunk type engine , < 0.1% is satisfactory
  • If > 0.5 %, immediate action should be taken and
  • It is maximum permissible content

What are the effects of fuel dilution in lube oil ?

Causes

  1. Poor atomization of a fuel injector and back leak through the fuel injector p/p plunger and barrel.

Effects

  1. Fuel dilution usually diesel oil.
  2. Lower viscosity and low fresh point
  3. Lower viscosity LO reduces this properties ( e.g load carrying capacity )
  4. Lower fresh point will case crankcase explosion.

How to remove contaminants

  1. Filtering: Removes large oil insoluble matter
  2. Gravity separation: Removes heavy matters, sludge and water
  3. Adding special additives: Reduce acids, sludge, finer oil insoluble matter
  4. Centrifuging: Removes sludge, foreign matter and water
  5. Water washing: Only for straight mineral oil or oil without additives, can remove acids.

What will you do if LO is contaminated with FW or SW ?

  1. Batch Purification must be done
  2. Renovating Tank heating and regular draining
  3. For SW contamination, Water Washing is required
  4. Sump to be opened and thoroughly wipe out.

What is meant by batch purification ?

  1. Firstly take the immobilization permit from the port authority.
  2. The entire oil charge should be pumped by the purifier or by main circulation p/p into settling tank.
  3. It should be allowed to settle for at least for 24 hours with heating about 60° C .
  4. Water and sludge should be drained out periodically.
  5. Cleaned the interior of the sump tank and carefully examined.
  6. The oil should be passed through the purifier at its optimum efficiency and than pump back into the sump tank.
  7. When sump tank empty, its interior should be cleaned and examined.

 When do periodic batch purification make ?

  1. If the oil is suspected from containing strong acids
  2. High insoluble contents due to poor combustion or water due to leak cooling system.
  3. It is also made at least once a year when cleaned and examined for sump tank.
  4. Suspecting biological contamination.

What is grease ?

  1. It is a semisolid lubricant consisting of high viscosity mineral oil and metallic soap with filler.
  2. Metallic soaps are compound of Ca, Na, Al.
  3. Filler are lead, zinc, graphite and molybdenum.

What is solid lubrication ?

  • Grease lubrication is known as solid lubrication

At what point cylinder oil is injected ?

  • The cylinder oil is feed to the piston at the time when the top two piston rings pass the lubrication holes in the cylinder during the piston stoke.
  • It is a limited lubrication.

What will be happen temperature is lower than pour point ?

The oil can not freely flow thus effect the pumping system (lubrication system)

Why viscosity of lube oil is important ?

  • Low viscosity is required for fuel oil in order to obtain good atomization at fuel.
  • Lube oil must be chosen which has a suitable viscosity for the working temperature for efficient lubrication.

How to maintain lube oil on board ships?

  1. L.O onboard test is carried out regularly.
  2. Regular cleaned L.O line filter.
  3. L.O purifier should be run during ship is in sea
  4. Maintain L.O purifier performance
  5. Periodic batch purification must be carried out & cleaned L.O sump tank once a year
  6. Maintain L.O temperature within limit
  7. Maintain good L.O cooler efficiency
  8. Keep good fuel combustion system

Why lubricating oil cooler is installed after lube oil filter ?

  • It is more effective to filter the hot oil, as pressure drop through the filter is less and filter is more efficient.

What will you do as 2/E, if main engine lubricating oil temperature abnormally high?

  1. Inform bridge & reduce engine speed
  2. Check engine overload or not (Exhaust temp:, fuel rack,..)
  3. Check L.O sump & L.O cooler & L.O purifier temperature (set value)
  4. Check L.O sump tank heating valve.
  5. Shut L.O cooler by-pass totally after stopping (or) too high temperature not fall
  6. Clean L.O cooler
  7. Check sump tank heating coil leakage
  8. Make L.O onboard test (esp  Viscosity)
  9. Check lubricating oil piping system leakage or blockage
  10. Make inspection & check bearing clearance & loosing attachment
  11. Check ampere (or) load when turn the turning gear

What will you do as 2/E, when increase sump lubricating oil level by marine engineer?

  1. Check piston cooling system (water)
  2. Check L.O purifier (gravity disc is correct or not) [L.O purifier water outlet sight galss]
  3. Check filling valve from storage tank
  4. Check L.O cooler/although oil pressure is greater than sea water pressure.

What will you do as 2/E, when decrease in sump lubricating oil level by marine engineer?

  • Check rate of decreasing if slowly decrease, fill up L.O and find the leakage without stopping engine.
  • If rapidly decrease, inform to bridge and stop the engine. Find the leakage and repair. Possible leakage points are:

* Bed plate crack (check engine room bilge)

* Piston cooling L.O system (check scavenge space & under piston space {entablature})

* L.O cooler & L.O purifier

* All pipes and connection

* Check L.O return valve from crankcase to sump tank close or not

* Check oil scraper rings & stuffing box

What will you do as 2/E, when decrease in lubricating oil pressure observed?

  1. Start stand by pump
  2. Change & clean L.O filter
  3. After engine stopping, check bearing clearance and L.O pipe connection
  4. Check L.O pump discharge & suction pressure
  5. Check L.O temperature

What is meant by hydrodynamic lubrication (full fluid film)?

  1. Moving surfaces are separated completely by the pressure of a continuous unbroken film or a layer of lubricant, generated by the movement of the two surfaces relative to each other.
  2. Essential requirement is formation of a wedge of lubricants between surfaces.
  3. Thickness of film 0.025 – 0.10 mm.
  4. Happens in lubrication for Journal Bearing, Bottom End Bearing, Tilting Pad Thrust Bearing      

What is meant by boundary lubrication?

  1. It exists when a full-fluid film lubrication is not possible.
  2. The sliding surfaces are separated by only a thin film of lubricant.
  3. High friction between the surfaces and some degree of metal to metal contact occurs
  4. Lubricant oil film decreases, until asperities of mating surfaces touch

What is meant by hydrostatic lubrication?

  1. A form of thick film lubrication, but instead of being self- generated, it is supplied from an external source by oil under pressure from a pump.
  2. Lubrication for Crosshead Bearings, with attached pump.

What is meant by elasto-hydrodynamic lubrication?

  1. Applies to line contact or nominal point between rolling or sliding surfaces, such as rolling contact bearings and meshing gear teeth.
  2. Thin film or squeeze film lubrication limits metal to metal contact.
  3. Elastic deformation of the metals occurs, and there is effect of high pressure on the lubricant.

What will you do as 2/E, if lube oil is contaminated with sea water?

  1. When sump oil is contaminated with SW, find sources of leakage (may be from LO cooler during ME stopped) stoppage and rectified.
  2. In port or while ME is stopped, transfer contaminated oil through purifier or transfer pump into settling tank, settled for at least 24 hours at about 60 C°, and water and sludge drained out periodically.
  3. Oil passed through purifier at 78° C with optimum efficiency, and pump back to settling tank.
  4. When sump tank is empty, interior cleaned and examined.
  5. Purified oil sent to laboratory and tested
  6. During this time, new oil should be used
  7. Oil should be reused, if lab results recommended that it is fit for further use. (Straight mineral oil 3% water washed. Additive oil 1% water washed).

What are the difference in Cylinder oil and System oil?

  • Cylinder oil is detergent / dispersant oil
  • System oil is straight mineral oil

What are the lube oil tests carried out on board Ships ?

Viscosity Determination

  • The simplest method is three tube rolling ball viscometer
  • Assuming the oil in the engine to be SAE 30 grade, one tube is filled with minimum safety viscosity (about SAE 20) and another one filled with maximum safety viscosity (about SAE 40). The last tube is to be filled with test sample.
  • All tubes are placed in a bucket of warm water until the oils are at the same temperature.
  • The three tubes then mounted on a tilted board and inverted. An internal hollow ball in each tube then rises to the surface.
  • If the time taken in the test sample is between that of the lower and upper limit oils, the oil is fit for further use. If not, it must be replaced.

Insoluble Content

  • A drop of sample oil is released from a given height onto a special filter paper.
  • Compare the result with the known varying insoluble content. The upper limit for straight mineral oil is 1% to 1.5 % and for detergent dispersant oil is 5%.

Water and other Contaminants

A known amount of sample oil in the test tube is heated and must be shaken the while doing so               

  • If there is no cracking, the oil is dry
  • If there is slightly cracking, the oil having a trace of water
  • If there is a heavily crackling, the oil is heavily diluted with water

 Acidity / Alkalinity Determination

Acidity is tested by extracting the acids from the sample by means of shaking with a known amount of distilled water. The acidic extract is then placed on a watch glass with an indicator solution of known strength. The mixture is then drawn up into a glass tube and its colour compared with a series of colour standards, each representing a known PH value, from which the sample can be determined quite accurately.

Another method   is :

A drop of indicator solution is placed on to blotting paper and this is followed by a drop of sample oil placed at the centre of the drop of previous absorbed indicator.

  • If the change of colour is Red, it is acid
  • If blue/green, it is alkaline.
  • If yellow/green, it is neutral.

Foreign Particles Test

  • This can be done by either Spectrochemical analysis or Ferrographic analysis, each giving particle size less than 10 uM to 100 uM range depending on the tests applied.
  • The most powerful technique is Inductively coupled plasma atomic emission spectrometry (ICP OR PES), which uses a direct spray technique to determine the wear and contaminant elements present in the oil. This technique will in the main only detect the particles below 10 uM size.
  • In ferrographic test, the sample is thinned first with some solvents and allowed to pass slowly down a slide surrounded by powerful magnetic field. Then it is examined by special microscope with red and green filters under lights. The shape of the particles is used to identify the source of the wear debris.
  • The advance ferrography method was added to the PFA (Progressive Fast Analysis) programme where all samples pass through the combination of two machines, a particle quantifier (PQ) and a rotary particle depositor (RPD). These test measures the induced magnetic moment of debris as deposited on a substrate or contained within a specific volume of liquid.
  • These machines provide accurate test by rotating the metal particles and then separating into three different sizes, Theses three bands of particles are examined by very powerful microscope to determine the type of materials and shape.
  • If more detailed examination is necessary, the debris may be subjected to a scanning electron microscope.

 

 

Reference:

Oral Guide by – MIN ZAR TAR

    HP P