A simple A–Z of the terminology we use throughout our marine product portfolio and support services pages, created by our product specialists and industry experts.



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Any substance containing hydrogen in combination with a non-metallic element(s) and capable of producing hydrogen ions in solution. An acid is capable of neutralising or being neutralised by a base.


In lubricants, acidity denotes the presence of acidic constituents whose concentration is usually defined in terms of an acid number.


A chemical compound or compounds added to a lubricating oil for the purpose of imparting new properties or enhancing existing properties.

Aniline point

The lowest temperature at which a hydrocarbon fluid is completely miscible with an equal quantity of aniline. The higher the reading, the lower the aromatic content, and hence the smaller the effect on rubber.

Antifoam agent

An additive used to suppress the foaming tendency of petroleum products in service. May be a silicone oil to break up surface bubbles or a polymer to decrease the number of small entrained bubbles.

Antiwear agent

Additives or their reaction products which form thin, tenacious films on highly loaded parts to prevent metal-to-metal contact.

API gravity

An arbitrary scale adopted by the American Petroleum Institute for expressing the relative density of an oil.

Degrees API =(141.5/rel.density@60°F) - 131.5


Hydrocarbons of ring structure having the smallest hydrogen to carbon ratio.


Some additives, particularly conventional detergent additives, leave behind a powdery residue after combustion. This residue is known as ash and can cause engine malfunction if allowed to build up in the combustion chamber, cylinder liner ports and turbochargers.

Ash (sulphated)

The ash content of an oil, determined by charring the oil and breaking the residue with sulphuric acid and evaporating to dryness. Expressed as % by mass.


Components of asphalt which are insoluble in petroleum naphtha but are soluble in aromatic solvents. They are hard and brittle and made up largely of high molecular weight polynuclear hydrocarbon derivatives containing carbon, hydrogen, sulphur, nitrogen, oxygen and usually nickel, iron and vanadium.



A biocide specifically formulated to kill bacteria.


A unit of volume measurement used for petroleum and petroleum products. A barrel = 42 US Gallons, ~ 35 Imperial Gallons or ~ 159 litres.


A compound which reacts with an acid to produce a salt plus water.

Base Number

A measure of the amount of acid-neutralising additive present in a lubricating oil, previously known as Total Base Number.

Base Stock (Base Oil)

Refined petroleum oil used in the production of lubricants and other products. The base stock may be used alone or blended with other base stocks and/or additives, to manufacture a finished lubricant.


The accumulation of substances within an organism.


The tendency of a substance to breakdown in the environment due to biological action.


A viscous liquid or solid consisting of hydrocarbons and their derivatives which is soluble in an aromatic solvent such as benzene. It is non volatile and softens when heated. Bitumen may be black or brown in colour and possesses waterproofing and adhesive properties. It is obtained from refinery processes but is also found as a natural deposit.

Black Oils

Asphaltic materials are added to lubricants used for open gears and steel cables to impart extra adhesiveness, giving them the characteristic black colour.


The intimate mixing of various components, including base oils and additives, in the preparation of a product of specified properties.

Boundary Lubrication

Lubrication between two rubbing surfaces without the development of a full fluid lubricating film. It occurs under high loads and requires the use of antiwear or EP additives to prevent metal-to-metal contact.



Eccentric lobes attached to a camshaft and driven by a crankshaft which are used in most internal combustion engines to open and close valves and sometimes operate fuel pumps.

Carbon Residue

Coked material remaining after an oil has been exposed to high temperatures under controlled conditions. Carbon residue is thus an indicator of the coke forming tendencies of an oil. It can be expressed as Conradson, Ramsbottom or Micro-Carbon Residue (MCR).

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Catalyst Fines

Small (typically less than 50 micron) particles of aluminium silicate used as a catalyst in catalytic cracking (cat cracker) refineries. They are sometimes carried over in the refinery process and can be found in residual fuels. They are very abrasive and can cause excessive wear in engine parts - particularly fuel pumps, injectors, cylinder liners and piston rings.

Centipoise (cP)

See Poise

Centistoke (cSt)

See Stoke

Cetane Index

A measure of the ignition quality of a distillate fuel, that is the relative ease with which the fuel will ignite when injected into a compression - ignition engine. Cetane Index is calculated from the API gravity and the mid boiling point of the fuel. High Cetane Indices indicate shorter ignition lags and are associated with better combustion performances.

Cetane Number

Similar to Cetane Index but is derived from a standard engine test rather than by calculation.

Cloud Point

The temperature at which a cloud or haze begins to appear when an oil, which has been previously dried, is cooled under prescribed conditions. Such a cloud or haze is usually due to the separation of wax from the oil.

Cold Filter Plugging Point (CFPP)

A measure of the ability of diesel fuels to flow at low temperature. A fuel with a low CFPP is capable of being used satisfactorily at low ambient temperatures and not cause blockages in fuel systems through the precipitation of wax particles.

Copper Strip Corrosion

A qualitative measure of the tendency of a petroleum product to corrode pure copper.

Crosshead Diesel Engine

Slow-speed marine diesel engine with separate lubrication systems for cylinders and crankcase. Invariably operating on the 2-stroke cycle these engines derive their name from the crosshead bearing which couples the piston rod and the connecting rod.


The top of the piston of an internal combustion engine above the firing ring which is exposed to direct flame impingement.

Cylinder Oil

Lubricating oil having a high BN for the lubrication of the cylinders of crosshead marine diesel engines and some types of trunk piston engines.



The ability of lubricant to withstand the formation of an emulsion with water. This property is measured by a test which times the separation of a well-mixed sample of oil and water, and gives a 'Demulsification Number' or 'Value'.


Mass per unit volume.


A substance added to a lubricant to keep engine parts clean. In engine oil formulations, the detergents most commonly used are metallic soaps with a reserve of basicity to neutralise acids formed during combustion.

Dew Point

The temperature at which water vapour in the air starts to condense to liquid.


An additive designed to disperse oil insoluble sludge in suspension, thus preventing harmful deposition in oilways.


Any product obtained by condensing the vapours distilled from petroleum or its products.

Distillation Range

The range of temperatures, usually determined at atmospheric pressure by standard apparatus, over which boiling, or distillation, of a liquid proceeds. Only a pure substance has one definite boiling point at a particular pressure. Petroleum distillates contain a complex range of hydrocarbon compounds and consequently a range of boiling points is determined which is different for different distillates.

Drop Point

The temperature at which a grease passes from a semi-solid to a liquid under specified test conditions



The ability of an oil or other non-water soluble fluid to form an emulsion with water.


A type of surfactant effective at producing stable emulsions.


An intimate mixture of fine particles of one liquid in another. An emulsion is said to "break" when the particles join up and the liquids separate.

End Point (Final Boiling Point)

The highest temperature indicated on the distillation thermometer when a light distillate is subjected to one of the standard laboratory methods of distillation.

Engine Deposits

Accumulations of sludge, varnish and carbonaceous residues due to blow-by of unburned and partially burned fuel, or from partial breakdown of the crankcase lubricant. Water from condensation of combustion products, carbon, residues from fuel or lubricating oil additives, dust and metal particles also contribute.

Engine Test

Use of an internal combustion engine to evaluate lubricants. Parameters such as piston ring groove fill, piston varnish, component wear, oil viscosity etc. are measured.


Compounds of alcohols and fatty acids which form the major constituent of many synthetic lubricating oils.

Extreme Pressure (EP) Lubricants

EP oils and greases contain additives (usually based on sulphur, phosphorus or chlorine) which, under the effects of high temperature and pressure, form a protective film on metallic surfaces, preventing metal-to-metal contact if the normal hydrodynamic film breaks down under high pressure.


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Fire Point

The lowest temperature at which an oil vaporises rapidly enough to burn for at least five seconds after ignition under standard conditions.

Flash Point

The temperature to which a combustible liquid must be heated to give off sufficient vapour to form a momentarily flammable mixture with air when ignited under specified conditions.

Floc Point

A measure of the tendency of an oil to flocculate - or precipitate wax - under prescribed conditions. It is mainly applicable to refrigeration oils.

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four ball EP test

Method for determining extreme pressure (EP) properties of fluids. One steel ball under load rotates against three stationary balls in the form of a cradle. Heated test fluid is subjected to a series of timed tests at increasing loads until welding occurs. Wear is described by scar diameter plus load to weld in kg.


The resisting force encountered at the common boundary between two bodies when, under the action of an external force, one body moves, or tends to move, relative to the other.

FZG Gear Test Rig

A method for determining the load carrying ability of lubricants. Calibrated spur gears are operated at fixed speed and controlled initial oil temperatures for 15 minute stages. The load on the gear teeth is increased after each stage. Performance is judged by the number of stages run up to a defined weight loss of the test gears or visual assessment of damage to the tooth flanks. Maximum number of stages is 12.


Gas Oil

A petroleum distillate having a viscosity and distillation range between those of kerosene and light lubricating oil. The distillation range of gas oils usually extends from 200°C to 380°C. Gas oil is used as a fuel in medium and high speed diesel engines and as a burner fuel in heating installations.


A lubricant composed of an oil, or oils, thickened with a soap or other thickener, to a semi-solid or to a solid consistency.



Chemical compounds which consist entirely of carbon and hydrogen. They form the basic composition of all fuels and lubricants derived from petroleum.



Incapable of being mixed to form a homogeneous mixture, eg. oil plus water.


A substance which is added in a small proportion to a lubricant to prevent or retard undesirable changes in the quality of the lubricant, or in the condition of the equipment in which the lubricant is used.



Kinematic Viscosity

Measure of a fluid's resistance to flow under gravity at a specific temperature (usually 40°C or 100°C).



The vertical surfaces of the piston crown and the areas between the piston rings.

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Any substance interposed between rubbing surfaces for the purpose of reducing friction between them.



US Military specifications.

Mineral Oil

Oil derived from mineral sources, notably petroleum.


Descriptive of substances, usually liquids, which mix together to form a homogeneous mixture.


'Multigrade' is a term used to describe an oil for which the viscosity/temperature characteristics are such that its low temperature and high temperature viscosities fall within the limits of two different SAE numbers.


Naphthenic Base Stock

A type of base stock prepared from Naphthenic crudes (crudes containing a high percentage of ring type aliphatic hydrocarbons). They are characterised by high specific gravity plus low viscosity index.

Neutralisation Number

A measure of the acidity or alkalinity of an oil. The number is the mass in milligrams of the amount of acid (HCI) or base (KOH) required to neutralise one gram of oil.


The process whereby nitrogen oxides attack petroleum fluids at high temperature, often resulting in viscosity increase and deposit formation.


A numerical scale devised by the U.S. National Lubricating Grease Institute for classifying the consistency range of lubricating greases. The higher the number, the 'stiffer' or more viscous the grease and vice versa.



A process by which oxygen combines with a material (eg oil), to form another substance.

Oxidation Inhibitor

An additive which slows down the rate of oxidation of an oil.

Oxidation Stability

A measure of resistance of a product to deterioration through exposure to air.


Paraffinic Base Stock

A type of base stock prepared from Paraffinic crudes (crudes containing a high percentage of open-chain aliphatic hydrocarbons). They are characterised by low specific gravity and high viscosity index.


Measure of consistency (hardness) of a grease. All penetration measurements are in inverse scale of consistency - that is, the softer the consistency, the higher the penetration number.


Also referred to as "mineral jelly" or "petroleum jelly", petrolatum is a salve like mixture of oil and microcrystalline wax obtained from petroleum.

Petter (WI)

Single cylinder gasoline engine. Evaluates oil oxidation by viscosity increases and copper/lead bearing weight loss. Duration is 36 hours at 1500 rpm with sump oil temperature at 137°C.


A measure of acidity or alkalinity in terms of the logarithm of the hydrogen ion concentration with the sign reversed.

pH 0 = extreme of acidity

pH 7 = neutral

pH 14 = extreme of alkalinity


The standard unit of dynamic viscosity, usually quoted as centipoise (cP).


Excessive smoothing out of the surface finish of the cylinder bore or cylinder liner in an engine to a mirror-like appearance, resulting in depreciation of the ring sealing efficiency and adhesion of the oil to the liner surface, leading to high oil consumption and possible ring scuffing. Bore polishing can be produced by excessive quantities of combustion products which build up on the piston lands and rub on the liner.


A synthetic lubricant produced by polymerisation of unsaturated hydrocarbons.

Pour Point

The lowest temperature at which a lubricant will pour or flow under specified conditions. Gives an indication of the lowest operating temperature for which an oil is suitable.

Pour Point Depressant

An additive used in a small proportion to lower the pour point of a lubricant by modifying the formation of wax crystals so that they do not agglomerate.

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The characteristics of an oil that permit satisfactory flow to and from the engine oil pump and subsequent lubrication of moving components.



Readily Biodegradable

A substance that rapidly breaks down in the marine environment through the action of micro-organisms.


Series of processes for converting crude oil and its fractions to finished petroleum products, including thermal cracking, catalytic cracking, polymerisation, alkylation, reforming, hydrocracking, hydroforming, hydrogenation, hydrogen treating, solvent extraction, dewaxing, deoiling, acid treating, clay filtration and de-asphalting.

Residual Fuel Oil

Very heavy fuel oils produced from the residue of the fractional distillation process rather than from the distilled fractions.

Ring Sticking

The situation when the piston grooves become sufficiently full of deposits or covered with lacquer to prevent the piston rings from moving freely.


The circular metallic elements that ride in the grooves of a piston and provide compression sealing during combustion. Also used to spread oil for lubrication of the cylinder liners.

Rust Preventive

Compound for coating metal surfaces with a film that protects against rust. Commonly used for the preservation of equipment in storage.



Sulzer Integrated Piston ring Wear detecting Arrangement. This equipment monitors the rate at which piston rings wear in crosshead engines, which in turn provides an indication of the cylinder liner wear rate and the performance of cylinder oils.


Abnormal wear occurring in engines due to localised welding and fracture. It can be prevented through the use of antiwear, extreme pressure and friction modifier additives.

Shear Stability

The property of resisting physical change under high rates of shear. When applied to a Viscosity Index Improver, it is the ability of the VI improver molecules to withstand breakdown into smaller molecules.


Oil insoluble products formed from lubricants and/or fuels used in internal combustion engines, and deposited on engine parts other than those in contact with the combustion space.

Solvent Extraction

Refining process used to separate reactive components (unsaturated hydrocarbons) from lube distillates in order to improve the oils oxidation stability, viscosity index and response to additives.

Stoke (ST)

The unit of kinematic viscosity, ie, the measurement of a fluid's resistance to flow defined by the ratio of the fluid's dynamic viscosity to its density; usually quoted as 'centistokes (cSt)'.

Straight Run

Fuels produced by distillation without cracking or alteration to the structure of the constituent hydrocarbons.


A compound able to reduce surface tension and commonly used to achieve emulsification, wetting or detergency.


Thermal Cracking (Visbreaking)

An oil refinery process in which the reaction is produced by the action of heat and pressure.

Timken Ok Load

Measure of the EP properties of a lubricant. Lubricated by the product under investigation, a standard steel roller rotates against a block. Timken OK load is the heaviest load that can be carried without scoring.


The ability of a substance to cause harmful effect across the marine food chain including algae, crustaceans and fish.


The science of lubrication, friction and wear.

Trunk Piston Diesel Engine

Medium-Speed, or High-speed, diesel engine generally using the same oil for both cylinder and crankcase lubrication, and utilising connecting rods to transmit piston power directly to the crankshaft rather than through a crosshead.


A piece of equipment in which a shaft is steadily rotated by the impact of a current of steam, air, water, or other fluid directed from jets or nozzles upon blades of a wheel or series of wheels.


Compressor driven by exhaust gas driven turbine supplying air at higher pressure to the engine to increase power.




That property of a liquid by virtue of which it offers resistance to motion or flow. It is commonly regarded as the 'thickness' of the liquid. Viscosity decreases with increasing temperature.

Viscosity Index (Vi)

An arbitrary scale used to measure a fluid's change of viscosity with temperature. The higher the viscosity index, the lower the rate of change of viscosity with temperature and vice versa

Viscosity Index Improver

An additive employed to raise the VI of a mineral oil and other products.






Commonly used name for zinc dithiophosphate, an antiwear/oxidation inhibitor chemical.