Lubricating oil properties and lube oil test carried out on board ship

Lubricating oil properties

Viscosity:

• Viscosity is the internal resistance of a liquid to flow.
• Viscosity varies inversely with temperature.
• Greater the temperature lesser the viscosity, lesser the temperature greater the viscosity.
• The viscosity index of oil is a number that indicates the effect of the temperature changes on the viscosity of the oil.
• Allow viscosity index signifies a relatively large change of viscosity with changes of temperature.
• In other words, the oil becomes extremely thin at high temperatures and extremely thick at low temperatures.
• On the other hand, a high viscosity index signifies relatively little change in viscosity over a wide temperature range.

High viscosity index - 85

Flash point:

• Flash point of liquid fuel is the minimum temperature at which sufficient vapours are produced and if ignited extremely gives off a spark.
• When considering fuels the flash point is determined to indicate the presence of the fire risk.
• This is particularly important when these type of fuels are used: Liquids with a flash point of more than 65 degree Celsius are called as long volatile liquid and the ones with a flash point less than 65 degree Celsius is called as volatile liquids.
• In ships, only non-volatile liquids are used.

                      High flash point of lube oil - 220degree celsius         

Pour point:

• Pour point is the temperature below which a liquid seizes to flow.
• If the liquid seizes to flow the oil pumps get overloaded and eventually get damaged.

Low pour point is -18 degree celsius

Total base number (TBN):

Total base number (TBN) is the indication of the oils ability to neutralize the effect of high sulphur diesel fuels. The higher a lube oils TBN, the more effective, it is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time.

TBN for ME crankcase oil is 6 mgKOH/gm 

 For ME cylinder oil: 10-20mgKOH/gm cyli (sulphur content o.5%), 70mgKOH/gm (sulphur content),

30mgKOH/gm(Aux engine same oil in crankcase and cylinder) 

Lube oil tests we carried out on board ship

There are some lube oil test facilities available onboard, which allows the ship personal to identify the problem and take corrective action.

These are some simple tests performed on board.

Flostick for assessing viscosity:

• The flostick is used to compare the viscosity of the used lube oil with that of fresh lube oil of the same grade.
• The basic method used is to compare the "rate of running down" of the used oil in relation to the fresh oil in a flostick.
• If the used oil does not run down to a specified mark, its viscosity is higher than acceptable and this may be due to the presence of high insoluble content, products of oxidation or ingress of fuel oil of higher viscosity.
• If the used oil passes another specified mark, its viscosity is lower than the acceptable and this may be due to dilution with a lighter distillate fuel.

Water content test:

• Water test kits onboard enable quick and reliable on-board measurement of the amount of freshwater or saltwater contamination of the system lubricating oil.
• The principle of estimating the amount of water is based on measuring the volume of gas generated by the chemical reaction between calcium hydride and the water that may be present in the lubricating oil sample.
• There are test kits comprising glass indicator tubes containing a chemical that reacts with the chlorides in the ingressed saltwater.
• A colour change indicates the presence of chloride(saltwater).

Alkalinity (minimum TBN) test kit:

• The alkalinity test kit is meant for easy determination of the extent of alkalinity (the minimum TBN) retained by the lube oil under test.
• This method can also be used for checking whether the lube oil meets the engine builder recommendations.
• The used oil is mixed with a specific amount of special indicator solution and an acid reagent in a test vial.
• A colour change will take place if the acid reagent neutralizes the alkaline additives in the lube oil.

• The achieved colour is checked against a colour comparator to assess if the TBN is above or below a certain level.
• The purple colour will show that the TBN value is adequate.
• The green colour shows that the TBN value is in borderline and yellow or golden colour formation indicates a very low value of TBN, which in turn shows that the lube oil is unsuitable for further use.

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