The throughput of the group in 1987 was 2,000 samples a year, which has grown to around 40,000 samples a year today. The Belgian company performs used oil analysis for Belgium, the Netherlands and Luxembourg, France, and other countries within an 8-hour transportation radius, so that results can be produced within a day.

WearCheck Belgium’s clients are mainly oil companies, as would be expected, who make up 64% of the work; the marine sector is 29%, and industry 7%. The distribution of lubricants and fluids that are analysed is: engine oils 62%, hydraulic oils 22%, transmission oils 12%, greases and emulsions 1%, and other oils 3%. The laboratory can handle over 90 different types and standards of test for the following materials: lubricating oils, water-emulsion and solutions, fuels, oils, and disel oil. Tests performed include property tests, such as aniline point, corrosiveness, and flashpoint, performance test, eg. Falex EP, and analytical determinations via spectrometry, microscopy, IR, and emissions ICP.

The acidity of an oil shows whether the oil is oxidised as a result of operation at high temperature, if there is a high percentage of moisture, or whether the oil has been in service for too long. The viscosity of the oil is a very important parameter and must be in conformity with the requirements of the machine builder. The alkalinity or the loss of alkalinity of the oil, proves that the oil is in contact with inorganic acids such as sulphuric acid or nitric acid.

Impurities can also come from the settings and processes in which the lubricants work, e.g. manufacturing can produce welding debris, assembling involves dust, perhaps also silicones or polishing powder, while maintenance can introduce impurities via dirty rags or deteriorated joints, and lubrication systems may need or involve aspiration, or open tanks.

The lubricant itself can produce or contain contaminants - wear, sludge (deterioration of the oil), soot, acids (oxidation of the oil, sulphur from fuel), temperature changes or extremes, fuel, anti-freeze, deterioration of packings and seals (e.g. deteriorating through the action of synthetic oils or brake fluids).

The type of contamination can vary according to the source. Thus dust, for example, can arise within a shipyard as sand, i.e. Si, Al. In metallurgy, one can find the oxides or iron. On a ship, there are problems with salt water. Industrial and automotive settings are filled with potential contaminants, for example chemical products, or coal powder. Liquid contaminants can include water, acids, solvents, anti-freeze.

Adhesive wear
This occurs as a result of metal-to-metal contact, due to overheating or insufficient lubrication. This in turn causes the formation of microwelds, with often a subsequent deposition of soft metal onto heavy metal (e.g., aluminum onto iron, lead onto steel). Consequently, there is a shearing of the junctions and a transfer of metal particles.

Figure 1 Abrasive wear

There are two types of adhesive wear - heavy, liberating relatively large metal particles (50 to 200 microns), called ‘scuffing’, and eventually leads to a failure of the engine; and moderate - the formation of very small metal oxides which is termed ‘soft’ or ‘normal adhesive’ wear (see Figure 1). Adhesive wear can be avoided by the use of an appropriate lubricant containing extreme pressure (EP) additives, and the choice of the correct viscosity oil.

Abrasive wear
This form of wear results from the grooving of a surface by hard asperities or by particles of rust or dust which have entered the oil. When these particles are very small, the phenomenon is known as ‘abrasive erosion’ (which is especially the case in hydraulic systems). Abrasive wear can be avoided by eliminating potentially abrasive particles through filtration.

Corrosive wear
This is chemical or galvanic attack, followed by the removal of the reaction products (chemical complexes) by mechanical action (friction). It can be avoided by the use of effective materials, also by the use of neutralizing additives in the oil. It may also be minimized by changing the oil in time.

Figure 2 Fretting

Wear by fatigue
This means the removal of spalled away particles by fatigue resulting from contact, aided by vibration, high pressure, high temperature and other aggressive conditions. This type of wear may be reduced by re-equilibration of the system.

Contact corrosion (fretting corrosion)
Corrosion due to contact means the removal of material between two surfaces which are in almost static contact but subject to mechanical vibration and oscillation. Consequently, there is oxidation of certain particles. Thus, for iron materials, there is an accumulation of ‘red powder’. An example of this is the bearings of cars transported by railway (see Figure 2).

Erosion by cavitation
The formation of cavities by entrainment of air of gas bubbles present in the fluid in movement is a destructive phenomenon, which can provoke the removal of material particles (see Figure 3).

Figure 3 Cavitation

Wear of electrical origin
This refers to the erosion by sparks, produced by inadequate electrical insulation in motors of alternators.

Acids
Too high an acidity of the oil can cause corrosive wear. These acids can be neutralized by the presence of an alkaline additive in the oil. The presence of acids will be measured by the Total Base Number, TBN.

Water
This is the worst enemy of the oil and the machine. Too high a water content can influence the viscosity of the oil by formation of an emulsion, and/or by reacting with certain additives. Water can restrict the functioning of inhibitors, and can also hydrolze additives containing zinc.

Temperature
High temperature and the presence of oxygen or water accelerate the oxidation of oil by the formation of acids and increasing the oil viscosity, as well as by provoking metal corrosion. For most mineral oils, oxidation starts at about 80°C, and doubles with every increase of 10°C. To avoid this problem of oxidation, one can use lubricants containing anti-oxidant additives and/or detergent or dispersant additives, or synthetic oils, which have better oxidation resistance at high temperatures, e.g., polyalphaolefin oils.

Those small particles are a good indication of general wear, except in cases of sudden metallic rupture, where there will be relatively more large particles liberated (50 microns and more). The human eye can detect particles of a size starting from 50 microns, which allows them to be visualized using more conventional means. Thus, complementary analysis of such larger particles can be done by spectrometry (after acid attack), by ferrography (or related systems) or by optical or electronic microscopy.

SAE viscosity grade crankcase oils

Industrial oils
The viscosity of industrial oils, by contrast, is mostly measured at 40°C, and must correspond with the ISO table below, i.e., the viscosity of an ISO class oil must be within the minimum and maximum for that class. (Moves are in hand to make the viscosity class statement contain more data, to reflect changes in the oil in use.)

It is evident that heavy dilution of the oil is unfavourable for the engine, since it involves a lower viscosity and reduces the resistance of the oil film. The principal causes of dilution are a defective fuel injection system, a defective air inlet (obstructed air filter), incomplete combustion due to too low a working temperature, and badly regulated valves, or insufficient compression.

Cooling water contains most often an anti-freeze based on glycol. Therefore a glycol test should be performed when water infiltration is suspected. The inhibitor in the anti-freeze agent is usually a sodium borate type.

Too low a TBN volume can be due to: heavy oxidation of the oil, when the oil has been in service for too long, of the oil level was insufficient, or due to a defective cooling system, producing overheating; use of a fuel containing a high sulphur content; use of an inappropriate lubricant; or contamination of the oil by fuel or water.

>5µ;>15µ;>25µ;>50µ;>100µ.

Or differentially:

>5-15µ;>15-25µ;>25-50µ;>50-100µ;>100µ.

The results of particle counting can be expressed according to either ISO 4406 or NAS 1638. According to ISO 4406, the results are expressed cumulatively, and the ISO classification is deduced from the two first classes, >5µ and >15µ, following the ISO table.

ISO 4406

According to NAS 1638, the results are expressed differentially, in five classes. In each class one can get a NAS quotation, and the NAS code is the figure given to the first class.

NAS 1638

this is differentially written as

According to ISO 4406, the classification is in this case 19/16. According to NAS 1638 the NAS class is 11.

• white or brilliant metal particles (demonstrating recent wear).
• black metal particles (already oxidized)
• rust particles
• silt (i.e., very small particles below 5µ, responsible for erosive wear)
• silica (sand, dust)
• polymers (from oil additives)
• welds
• paint flakes
• other impurities (fibre, plastics, and so on)

APPENDIX:
INTERPRETATION OF AN OIL ANALYSIS REPORT

Wear metals
The determination of the wear level is related to several parameters, e.g.

• make and type of engine
• running hours or kilometrage of the oil
• running hours or kilometrage of the engine
• oil addition (top-up)
• volume of the sump
• oil type
• individual particularities: running-in period, mechanical intervention
• place where the sample has been taken

Water content
Limit = 0.2%

TBN
50% of decrease is tolerated (in comparison with the TBN of the fresh oil).

Dilution
Diesel fuel (a) on the road - 0 to 4% = normal, >4% = problematic (b) stop-go service >6% = problematic

Gasoline (a) on the road - 0 to 4% = normal, >4% = problematic (b) stop-go service >8% = dangerous

TAN
1 mg KOH/g for a non-additivated oil, 2 mg KOH/g for an additivated oil.

Water content

Particle counting
The limits for particle counting are generally given by the manufacturers of the equipment. The following limits can apply.