Technical information....

Oil analysis tests......

This is where we have outlined in more detail the processes behind a typical oil sample taken from an engine.

Wear Metals

Perhaps the most important and central test of used engine oil analysis is the analysis of wear metals, contaminants, and additive elements using ICP-OES (Inductively Couple Plasma Optical Emission Spectrometry), which analyses over 20 elements simultaneously by nebulising and vaporising a diluted sample into a very hot argon plasma. This atomises, ionises and excites the elements which in turn release this absorbed energy in the form of light, the wavelength of which is specific to the element in question, and the intensity of which is proportional to the concentration.

The level of wear metals used to assess abnormal conditions differs with application; indeed they differ slightly for particular units of one type. The information required must, therefore, be built up for each unit by regular monitoring, and guidelines developed for each unit. Nevertheless, regular condition monitoring on a particular machine ultimately relies, not on the actual metal values, but on the sudden CHANGES from the average.

Only particles <10 micron can be measured via this technique: when catastrophic failure occurs larger particles are produced. Condition monitoring would not be able to predict this event but could be used to help detect the cause.

Physical Properties

This starts with a visual assessment of lube oils to identify gross contamination. Large metal and dirt particles and foreign bodies that are too big to be analysed by ICP-OES would go unnoticed without this simple check.

Viscosity

The resistance to flow is measured by the time taken for a given volume of oil to flow under gravity between 2 points in a calibrated viscometer tube.

Viscosity measurements are essential to establish the correct grade of the oil in use, eg SAE 30 or 15w40. Slight changes in viscosity are to be expected during use, but abnormal changes must be detected and reported.

Abnormalities are indicative of one or more of the following problems:

Overheating

Fuel Dilution

High Insolubles

Excessive use

General contaminants

Wrong Oil Grade

All lubricating oils have a standard unused oil viscosity which is used to determine tolerances in the analysis of the in-service oil:

A 15% change from the unused is considered to be cautionary and a 20% change considered abnormal. For example an oil of ISO 100 grade will be subject to the following limits:

Normal - between 85Cst and 115Cst (Centistokes, the units of kinematic viscosity)

Caution - between 80Cst and 85Cst or between 115Cst and 120Cst

Serious - less than 80Cst or more than 120Cst.

Acidity & Alkalinity

The TAN test is usually performed in relation to two methods, IP139 and IP177 and can determine if any acidic compounds are forming within the machine, which will reduce the life and quality of the lubricating oil.

TBN

The TBN test determines the amount of reserve alkalinity present in the lubricant. This reserve alkalinity is part of additive packages found in engine oils and its function is to protect the crankcase from the corrosive acidic components produced in the combustion chamber.

Diesel fuel contains sulphur; this burns and forms SO2 and SO3 in the combustion chamber of the engine. Diesel also burns to produce CO2 and water, while the Nitrogen from the air produces Nitrogen Oxides (NOX) compounds. The water and Sulphur Oxides mix to form Sulphuric acid, and the Nitrogen Oxides combine with the water to form Nitric acids.

This acid mixture would destroy engine parts rapidly. Therefore it is essential to remove these acids as quickly as possible. This is done by introducing an alkali solution into the oil to neutralise the acids before they attack the engine. All unused oils will have a reference TBN value: it is the change in this value from the unused, which measures the reserve alkalinity remaining in the lubricant.

The TBN value is obtained by titrating the engine oils with acids and the results are expressed as mg/KOH/g.

Contamination

In addition to wear metals, ferrous debris, and combustion products in lubrication oils, other contaminants can include:

A major cause of engine or machine failure is dirt contamination. It acts as an abrasive on most metallic surfaces and can cause severe problems. The presence of excessive dirt contamination can be picked up by a visual appearance of a sample but can also be seen in the spectrometric (ICP-OES) analysis of the samples.

The type of dirt found depends on the material being handled and the working conditions of the equipment, but generally dirt is silicon based. Off-highway plant machinery and road vehicles are generally in contact with silicate dirt or grit from roads and concrete. Special processes, however, may also include titanium oxides, limestone or coal etc as the major dirt component, whilst marine vessels will of course include cargo debris, sand and salt.

It is essential to be aware of these factors during the diagnosis of results. We therefore base our interpretations on the analysis of over 20 elements, which cover most, if not all of these possibilities.

A ratio of 3:1 of Silicon to Aluminium on a sample report is indicative of environmental dirt.

Fuel Dilution is measured by various methods namely, viscosity, FTIR (Fourier Transform Infra-Red Spectrometry), flash point, fuel sniffer and Gas Chromatography. These tests are essential to detect over rich mixtures, faulty injector systems and leaking pipework. An excess of fuel dilution can lead to poor lubrication and excessive wear or failure.

Abnormal - More than 2% fuel

Serious - More than 4.5% fuel

Glycol is one of the worst enemies of lubricating oils. Found in most antifreeze solutions, glycol can enter oil supplies in many of the same ways water does. When mixed with oil at operating temperatures, the glycol/oil mixture changes chemically to form highly corrosive sludge deposits.

Rapid deposit formation causes a marked increase in oil viscosity (thickness) impairing the oil´s flow characteristics, totally plugging up component systems, causing lubricant starvation. The resulting excessive wear problems are sometimes catastrophic.

If present for any length of time, these deposits will readily bond themselves to moving parts, totally displacing the oil and in extreme cases, causing components to seize.

If a coolant leak is the source of the water contamination, then glycol may be present.

To check for glycol we can analyse the samples with FTIR (Fourier Transform Infra-Red Spectrometry) or Gas Chromatography.

Water can be found as a contaminant in any lubricated system and can rapidly reduce the lubricants’ quality as well as increasing the levels of wear debris in the equipment.

Water can be introduced into a system via poor sampling or storage procedures, or can be derived from the atmosphere, sea or rainwater and can be introduced by leaking seals, and air breathers with no desiccators. Water is also a problem with machinery which has cooling system problems.

Water can readily be detected by the simple crackle test. Indeed, qualitatively, the crackle test is an extremely reliable test. Simply by dropping an oil onto a hot plate at over 100oC will cause the water if present, to crackle (just like dropping your chips into a chip pan!)

No crackling noise confirms the there is less than 500ppm of water present. However it does not mean that there is no coolant leak: the water may have evaporated off from the hot oil.

If water is present, it is then quantified by various laboratory methods to determine the concentration. In some larger turbine systems it is necessary to measure the water down to single figures of parts per million. Such samples are analysed using a Karl Fischer instrument.