In some cases the analytical data will identify an obvious problem. A high level of water combined with high levels of boron and/or sodium is a strong indication of contamination from anti-freeze, often from a coolant leak. A high particle count and high levels of silicon indicate contamination from dirt or dust, probably from a plugged air filter or someone leaving the reservoir cap off.

In most situations, however, the analytical data alone from an individual sample does not provide enough information to make more subtle judgments about oi or equipment condition. To provide more meaningful information about operating conditions, it is necessary to compare current sample data to previous samples, or to data from the same type of equipment in similar service. This is particularly important in the use of wear metals data, since normal wear metal levels may vary significantly between different types of equipment and different applications.

These subtle judgments of oil and equipment condition, while more difficult to determine, offer the greatest potential for reducing system downtime and increasing equipment life. For instance, by continuously monitoring the levels of wear metals such as iron, lead, tin and copper, it is possible to detect the early stages of bearing failure. Awareness of an impending bearing failure can allow proper maintenance scheduling without unexpected or excessive downtime. In some situations, replacement parts can be ordered in advance, reducing the amount of downtime even more. With unscheduled downtime costs ranging rrom hundreds to even thousands of dollars an hour, this advance warning can be worth many times the cost of the entire oil analysis program.

One way for an analytical lab to improve the reliability of their recommendations is to compare individual sample data to other similar operations. Comparisons can be made of engine types, operating climate or environment, severity of service, frequency of use, and/or fleet size. Industrial operations can be compared according to equipment tyupe, intermittent or continuous service, operating environment and severity of duty. In this way one operator benefits from the experience the lab has had with other oil analysis customers.

Comparisons can be made of engine types, operating climate or environment, severity of service, frequency of use, and/or fleet size. Industrial operations can be compared according to equipment type, intermittent or continuous service, operating environment and severity of duty. In this way one operator benefits from the experience a lab has had with other oil analysis customers.

In summary, experience is the key to effective data interpretation. Lab technicians must have experience interpreting data from a variety of equipment types, each having different operating conditions and system problems. The more experience they have, the greater likelihood that they will have seen your particular type of operation before and solved similar problems.

The following outlines data interpretation for some of the most common applications. The outlines provide only the most general information about oil condition and the sources of contamination or wear metals, and are not meant to be recommendations for specific equipment or operating situations. These outlines should be helpful, however, in your understanding the specific data interpretation that your lab will provide with each sample analysis.

Periodic oil analysis was originally used as a tool to detect diesel and gasoline engine problems before they became serious and expensive. Tests could determine excessive fuel dilution, coolant contamination and dirt ingestion, and would also provide information on engine wear as well as whether or not the oil needed to be changed.

The value of oil analysis has steadily increased due to the rapidly increasing cost of equipment, labor and downtime. In addition, the higher cost of lubricants and the growing acceptance of synthetic based oils has made it much more practical and cost effective to change oil only when needed, rather than at a fixed time interval. The interpretation of oil analysis data, therefore, is directed at three areas in particular: oil condition, contamination, and engine wear.

Engine oil condition
One measure of the degradation of an engine oil is its increase in viscosity. This increase is sue partly to the evaporation of lighter base oil fractions as well as the loss of volatile oil degradation products. In addition, some of the degradation products chemically combine to form long polymers that are extremely viscous. Normally a 25% increase in viscosity is a warning that the oil is reaching the end of its useful life.

Boron -- Oil additive, anti-freeze additive Zinc/phosphorus/ calcium/magnesium/ barium -- Oil Additives Iron -- cylinders, liners, pistons, rings, valves, valve guides, anti-friction bearings, gears, shafts, clutch plates, rust Aluminum -- Pistons, bearings, blower/turbo chargers, pump vanes, thrust washers Chromium -- Compression rings, anti-friction bearings, shafts, coolant additive Copper -- Bearings, bushings, thrust washers, valve guides, injector shields, oil cooler tubes, wet clutches Lead -- Bearings, platings, gear oil additives, fuel additives Tin -- Bearings, platings Silver -- Anti-friction bearings, silver solder, wrist pin bushings Silicon -- Sand, dirt, anti-foam oil additive, gasket sealant material, anti-freeze additive

Most engine oils are formulated with a variety of additives that enhance lubricity, retard oxidation and corrosion, and reduce the tendency for sludge and deposit formation. The level of the more critical additives can be determined by monitoring the total base number (TBN), which is essentially a measure of the ability of the oil to continue to resist metal corrosion. Through use, the TBN will decrease, indicating a depletion of the oil's additive package. Generally, most laboratories will suggest the oil be changed when a 50% reduction in TBN is noted, or it falls below 2.0. different engine oils may have different additive packages and therefore different TBN's, so it is important to always measure change in TBN from new. The TBN of an engine oil may be obtained from data sheets, or measured by analyzing a sample of new oil.

Additive levels may also be measured with spectrographic metals analysis. Normal metals analysis will detect the levels of zinc, phosphorous, calcium and barium, which are common elements in most additive packages. Again, a 50% reduction in parts-er-million of metals indicates that the oil should be changed.

Engine oil contamination
The most serious engine oil contaminants are fuel, coolant and dirt. Fuel dilution is serious in that it can significantly reduce oil viscosity and cause excessive engine wear. Since most engine oils gradually increase in viscosity over their useful life, a noticeable reduction in viscosity is a strong indication of fuel dilution. In some cases there will be a detectable fuel odor from the oil sample, but if there is any doubt, additional testing can confirm the presence and level of fuel dilution.

Coolant is one of the most common engine oil contaminants and probably the most serious. The water reduces lubricity and causes metal corrosion, while the glycol breaks down at high engine temperatures and forms sludge. In most situations simply monitoring water content is not reliable enough, since high engine temperatures will vaporize water quickly and keep detectable levels as low as 0.05%. coolant contamination levels can be measured by doing a chemical analysis for the presence of glycol, or measuring the level of boron or sodium spectrographically. Since some oils contain boron or sodium additives, a significant change in their spectrographic levels is a good indication of a cooler leak.

Dirt is probably the most common engine oil contaminant, and high levels can lead to excessive engine wear. The most effective way to detect dust or dirt contamination is to monitor the silicon level by spectrochemical analysis, though some tests can indicate total solids by centrifugal separation or filtering through a fine membrane filter. Contamination levels will vary according to the type of engine and application, with off-highway equipment often having the highest levels. Again, it is important to measure the change in silicon or solids level, rather than look at any individual analysis. Only when there is a substantial change in this level is it time to look for missing reservoir caps, check for plugged or missing air filters, and consider changing the oil.

Normal engine wear
In many instances the most important value of periodic oil analysis is to keep the equipment running and reduce unexpected downtime. Analysis of the types and levels of wear metals can be used to determine which engine components are wearing and if the level of wear is becoming critical. In some cases this has made the difference between minor component repairs and major equipment overhauls.

Most tests measure wear metal levels spectrographically. One technique is atomic absorption in which the oil sample is burned in a high temperature flame, and the equipment detects how much energy was absorbed by a particular chemical element such as tin or iron. Another technique, emission spectroscopy, simultaneously measures the levels of as many as 18 different wear metals and contaminants. Both techniques provide the level, in parts-per-million, of each of the common metals found in engine parts. These include iron, aluminum, chromium, copper, lead, tin, nickel, and silver. The chart provides a summary of the most common wear metals and where they can be found in an engine.

These charts also indicate that effective wear metals analysis is more than simply plotting analytical data on a graph. Wear metals can be generated from any of a dozen different parts and engine locations, making it difficult to isolate any one part that is wearing excessively. Most labs will therefore compare the wear trends to similar operations using the same type of equipment in order to more reliably predict component failure. Because of this, it is extremely important and valuable to work with a lab that has many years of experience, and extensive experience with your particular type of equipment and operation. Some of the larger labs have data from hundreds of thousands of samples in their files, and your operation will benefit from the practical experience that these analyses have provided.

One final note. The interpretation of spectrographic oil analysis data is perhaps the most subjective of any oil analysis technique. Claims for accuracy and reliability will vary from lab to lab, and probably from salesman to salesman. The time to question the experience and reliability of any particular lab is before you begin a program, rather than after the results of your first analysis comes back. There are countless stories of operators who neglected to act on lab recommendations, only to experience engine failure and costly equipment downtime. It is important to trust the lab you work with, and to be able to freely discuss your operating requirements with their technicians. Only with that type of open dialogue can you take advantage of the full benefits that periodic oil analysis can provide.

Periodic hydraulic fluid analysis is used primarily to determine when to change the fluid and to detect contamination before it seriously affects system components. These considerations have become even more significant with the rapidly rising cost of hydraulic fluid, new restrictions on waste oil disposal, and the ever increasing cost of equipment downtime and repair. The interpretation of oil analysis data, therefore, is aimed at two areas in particular: fluid condition, and type/level of contamination.

Hydraulic fluid condition
One measure of the degradation of a hydraulic fluid is its viscosity, often measured in Saybolt Universal Seconds (SUS). In most cases the viscosity should increase slowly, and at a bulk system temperature less than 150 deg. F, service life should be in the thousands of hours. Normally a 10% increase in viscosity is an indication that the fluid is breaking down and nearing the end of its useful life. Any significant change from this steady and gradual increase usually means there is a hot spot in the system, or there has been contamination from fuel or other fluid types. Higher temperatures can result from the failure of the cooling system, loss of shielding from high temperature areas, or simply a change in operations that is making the fluid run hotter. Fuel dilution will lower the viscosity, while contamination from other fluids can either raise or lower the viscosity depending on their type.

To further define the cause of a change in viscosity, it is helpful to look at the change in total acid number (TAN), measured as milligrams of potassium hydroxide per gram of fluid. As hydraulic fluids break down they form acidic byproducts, and the greater the degradation, the greater the level of acidity. Therefore, a significant increase in viscosity without a simultaneous increase in acidity is often an indication of contamination from fuel or other fluid types.

Some hydraulic fluids have additives which are themselves acidic, so the most meaningful measure is the change in acidity from new fluid. A overall change of more than 1.0 mgKOH/gm in acidity is a warning that the fluid is nearing the end of its useful life, and should be scheduled for a change. One final note, acidity increases more rapidly as the fluid is degraded. If it too 5000 hours for the acidity to go from 0.10 mgKPH/gm to 0.60, it will take it considerably less then 5000 hours to increase further to 1.10 mgKOH/gm.

Hydraulic fluid contamination
Contamination is one of the greatest threats to a hydraulic system. The most common contaminants are water and dirt, though serious damage can also be caused by adding the wrong fluid type, fuel dilution or seal deterioration. The chart above indicates that the most common characteristics are and where they are most likely to come from.

Water is one of the worst contaminants because it is a poor lubricant and promotes metal corrosion. Most petroleum hydraulic fluids will dissolve or suspend less than 1% water, and a good warning level is 0.2%. Gross water contamination will often not show up in oil analysis because the water will collect in a layer on the bottom of the reservoir where samples are not normally taken. Water contamination gives a milky white appearance to petroleum fluids which can be detected visually, or there are a number of common laboratory tests which can be run.

Another measure of contamination is the particle count. This can be done visually with a patch test kit, or with any of several automatic particle counters. Small particles (less than 5 microns) are the most damaging to close tolerance valve surfaces, while larger particles can accumulate and restrict flow through small orifices. In either case, high levels of particles are often damaging to system components.

The patch test is the easiest to use, and can even be done on site. A sample of oil is passed through a filter patch, collecting most of the particles and forming a gray layer on the surfaces. The patch is compared to a series of standards which represent different particle levels, the darkest representing the greatest contamination. In addition to providing a general level of contamination, the patch can be viewed with a microscope to further define the type and origin of the particles.

Some labs provide a similar patch test service in which they actually count the different particle sizes with the help of a grid on the microscope. This provides more detailed information than comparing colored patches, and often indicates the type and origin of much smaller particles. Automatic particle counters are also available which provide accurate counts in a much shorter time period. One drawback of the automatic counters is that there is no visual capability to further define particle type and origin.

In each case, particle counts provide the user with a lot of numbers and information that needs to be properly interpreted. It is important to recognize that each hydraulic system has its own "stead-state" particle level at which the system will normally operate. In this condition the level of newly generated particles is offset by particles that are removed by filtration, settle into low spots, and become small enough that they actually dissolve in the fluid. This "steady-state" may vary from system to system, and can be properly determined only by analyzing several samples over a 3-6 month period. The experience of the lab technicians is also quite helpful in defining what the normal particle levels should be.

Subsequent oil analysis will then monitor changes in particle count which could indicate outside contamination. The level and size of the particles is a measure of the seriousness of the problem. Further visual analysis can determine if the particles are metallic, sand or dirt, or deteriorated seals or packings. In many operations, contamination will start out as relatively large particles (over 25 microns), which will be gradually pulverized into much smaller particles (less than 10 microns). Contamination can also create metallic wear particles which normally are less than 10 microns in size.