The Value of Oil Analysis & Wear Particle Analysis

Oil Analysis is a series of tests designed to measure the physical properties of lubricating oil. The presence of wear, corrosion, and contamination can be detected, as well as an assessment of the oils serviceability. Testing of a new fluid can provide information about oil quality and application.

Wear Particle Analysis is a microscopic evaluation of wear debris and solid contamination separated from lubricating oil. By examining such debris, many determinations can be made about the condition of a piece of equipment.

Both Oil and Wear Particle Analysis have the distinction of being able to detect oncoming problems before any damage occurs. Early warning signs of abnormalities will show up in oil long before the equipment heats up or starts to vibrate.

Testing personnel will take the oil sample directly from the sample point, follow it through the testing process, write a report on the oil and unit condition, and finally hand deliver the report and answer any questions there may be about the sample or testing.

Standard Tests Include:

SpectroChemical Analysis

Method: Inductively Coupled Plasma (ICP)

Instrument: Spectrometer

Description: Oil is introduced into a plasma flame causing the atoms to become more active and emit light. Light intensity is measured at twenty different frequencies, each characteristic of an individual element. Readings are reported in parts per million.

Significance: By measuring levels of elements associated with wear, contamination, and additives, several determinations can be made concerning the condition of the oil and the unit being sampled. Specific elements tested and typical sources are listed below.

Wear Metal Limits

Typical levels of wear metal elements can vary greatly depending on the type of equipment being sampled. For example, a differential will normally have much higher levels of iron than an engine.

Levels of wear metals can even vary in different units of the same type, depending on oil hours, operating conditions, and loading levels to name just a few. For this reason it is impossible to establish firm limits for any piece of equipment based solely on the equipment type. To take full advantage of monitoring wear metals, a trend should be established to provide an operational baseline of data. This will ensure detection of abnormal wear rates as they develop.

While a baseline should be established for most accurate analysis of wear metal levels, the table shown below indicates some typical limits for various equipment types. These limits are used as guidelines when a first-time sample is submitted for testing. These limits may be adjusted according to additional information such as oil time or original equipment manufacturer (OEM) recommendations.

Typical Wear Metal Limits

Viscosity

Method: ASTM D-445

Instrument: Viscometer

Description: Oil is drawn into a calibrated capillary tube in a constant temperature bath. Once the sample has come to temperature it is pulled to the top of the capillary and allowed to flow back down past two timing sensors. The viscosity is the product of the flow time and tube calibration factor. Results are reported in centistokes (cSt).

Significance: Viscosity is defined as a fluids' resistance to flow. It is considered the most important property of a lubricating oil, and a key indicator of an oils' serviceability. Engine oils are assigned an SAE grade based on their viscosity at 100° C. This rating is generally referred to as the oils' weight. Industrial oils are typically rated by an ISO grade representing its viscosity at 40° C. The chart below outlines several common oil grades and their acceptable viscosity ranges (these limits are for new oils).

High Viscosity: When an oils viscosity increases, it means the oil is getting thicker. The most common cause of oil thickening is oxidation. Oxidation is a natural process and is the principal reason that oil changes are necessary. High operating temperatures, overloading, and water/coolant contamination are examples of conditions that can accelerate oxidation causing oil to thicken prematurely. Contamination with soot or excessive dirt can also cause increased viscosity. High viscosity can cause overheating, restricted oil flow, and can ultimately lead to catastrophic failure.

Low Viscosity: Decreased viscosity (oil thinning) is typically the result of contamination with fuel or a different grade oil. Low viscosity can lead to increased friction, overheating, metal to metal contact, and ultimately failure.

Water by Karl Fischer

Method: ASTM D-1744

Instrument: Karl Fischer Titrator

Description: A sample of oil is introduced into a titration chamber in known volume. The solution is titrated with Karl Fischer reagent to an electrometric endpoint. The amount of reagent used and the sample volume are calculated and converted to ppm or % by volume.

Significance: Moisture in a lubricating oil can cause oxidation of the oil, corrosion of equipment components, and can alter the load-handling ability of an oil. By monitoring oil for water contamination action can be taken before any damage occurs. In most systems, water levels should not exceed 0.05% (500 ppm).

Sources: As a unit cools after operation, the change in temperature can cause water condensation. Normally, moisture evaporates when unit comes back to operating temperature. However if the unit operates at low temperatures or has a large reservoir, water can accumulate and cause damage. Water can also be introduced to a unit through internal water leaks. Examples in an engine would include a cracked block, deteriorating head gasket, or corroded oil cooler. In the case of an engine, the coolant can also be detected by spectrochemical analysis and glycol testing.

Particle Count

Method: NFPA/T2.9.16-1995 & ISO 4406 (OLD) For new table 4406-1999

Instrument: Automatic Particle Counter

Description: The sample is passed through a small orifice that has a light source on one side and an optical sensor on the other side. Particles interrupting the light beam are counted and size is determined by the duration of the interruption. The particles are categorized by size and totals are calculated in 5 size ranges. Results are reported as particles per ml or particles per 100 ml. ISO cleanliness codes are also assigned based on particles in 5 and 15 micron ranges.

Significance: Particulate contamination can cause operational problems in many types of equipment. ISO cleanliness codes allow us to monitor particle levels to ensure that they stay within acceptable ranges. Equipment manufacturers provide recommendations for cleanliness in the form of ISO cleanliness targets. It is recommended to follow the guidlines of the equipment manufacturer. Some typical ISO targets are listed below.

High particle levels can come from two sources, wear and contamination. Particles associated with wear are typically larger in size than those from contamination. High levels of particles in the 5 micron range would indicate a contamination problem, while excessive levels in the higher size ranges may indicate a wear related problem. SpectroChemical analysis and Wear Particle Analysis can help to identify the source of high particle counts.

Cleanliness Correlation Table:

Wear Particle Analysis

Method: Analytical Ferrography

Instrument: Bi-Chromatic Microscope

Description: The sample is diluted in a filtered solvent and passed over a specially treated substraight positioned in a strong magnetic field. The debris is deposited along the substraight in an increasing size distribution. The debris found on the slide is evaluated microscopically for size, color, shape, and condition. Conclusions are drawn as to component condition and wear rates.

Significance: By analyzing wear debris found in oils, many determinations can be made regarding the condition and wear rate of the unit being tested. Conditions such as overloading, overheating, poor lubrication, surface fatigue, and abrasive wear can be identified. The charts below outline typical wear and contamination particles.