The key element in any analysis program is to balance accuracy with cost and the time required to complete each test. In most situations the real value of the data is in determining trends rather than in the accuracy of any one individual test. There is little value in measuring viscosity to within +/- 0.1 Saybolt Universal Seconds (SUS) if the normal sample variation is +/- SUS. In fact, pre-occupation with excessive test accuracy can undermine the ability to distinguish longer term trends in oil properties.

Another important aspect is the importance of the equipment being sampled. A large bearing on a 10-cylinder diesel is much more expensive to replace than the main bearings on a gasoline engine. An oil analysis program should take into consideration the cost of equipment repairs and downtime, and the importance of that particular equipment in the overall plant production cycle. critical equipment may warrant specialized oil analysis testing that would not be cost effective on less important equipment.

In general there are two different classes of analytical tests, those that measure the physical properties of the oil, and those that measure the level of contamination. The physical properties are a good indication of the condition of the oil, and are often used to determine oil drain intervals. Some of the most common physical property tests are: viscosity, total aid number (TAN) and total base number (TBN). The level of contamination is important in identifying equipment malfunctions such as radiator leaks or damaged air filters, and in determining equipment wear rates. Common contamination tests include: water content, fuel dilution, particle count and wear metals analysis.

In some cases independent laboratories have set up standard programs that offer a series of tests for a fixed cost. By running hundreds of samples through each procedure they can offer reasonable accuracy at a much lower cost per sample. In addition, the user benefits by having his data in a format that can be easily compared to other similar operations. Standard programs are most common for diesel and gasoline engine oil analysis, though there are a growing number of programs for turbine oils and hydraulic fluids. Costs vary from $10 per sample for some engine oil analysis, to over $100 per sample for some hydraulic fluid programs.

Engine Oils
Periodic engine oil analysis is an important element in extending oil drain intervals and prolonging engine life. Rising prices for motor oils and questions of future availability have made it increasingly important to extend oil drain intervals whenever possible. Periodic analysis is the only reliable method to determine exactly when the oil needs to be changed. In addition, analysis of the types and levels of contamination can identify potential engine problems before they become serious enough to cause downtime and major repairs. An effective engine oil analysis program should include the following tests:

Viscosity -- One measure of the degradation of a motor oil is its viscosity, often measured in Saybolt Universal Seconds (SUS) at 100 deg. F. As petroleum based motor oils bread down their viscosity increases. Normally a 25% increase (getting thicker) is a warning that the oil is reaching the end of its useful life. Synthetic or partial synthetic base motor oils also increase in viscosity when they degrade, but the rate of increase is usually much slower. Fuel dilution can cause a reduction in viscosity and should be monitored as well. In most cases, however, additive depletion or contamination will be the factor determining oil change interval.

Total Base Number -- Most motor oils are formulated with a variety of additives that enhance lubricity, retard oxidation and corrosion, improve viscosity characteristics and pour point, and reduce the tendency for sludge and deposit formation. The level of additives can be determined by measuring the total base number (TBN) or the oil, usually expressed in mgKOH/gm. Since there are many different oil formulations, it is best to measure the change in TBN from new. The TBN of the new oil should be listed in the data sheets, or can be obtained by sampling the oil just after an oil change. A 50% reduction in TBN (or down to a TBN level of 3 or 4) is a warning that the additives are becoming depleted and an oil change should be scheduled.

Coolant Contamination -- Cooling system leakage is one of the most serious hazards for engine lubrication. The water reduces lubricity and causes corrosion of metal parts. The glycol from anti-freeze breaks down at high engine temperatures and forms sludge and deposits. In most cases analyzing for water content is not reliable enough, as high engine temperatures can vaporize water quickly and keep detected levels as low as 0.05%. One alternative test measures the level of glycol in the oil, while emission spectroscopy will detect levels of boron or sodium from the additives in antifreeze. In either case, once coolant leakage is detected, the leak should be repaired and the oil changed.

Wear Metals -- 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. Most tests measure levels of iron and aluminum to determine the amount of wear in piston rings and cylinder walls. High levels of cooper, lead and tin are indications of main bearing wear and represent a more serious problem. Some tests also determine the level of silicon as a measure of ingested dirt or dust, the levels of lubricant additives and the levels of sodium or boron which indicate contamination from antifreeze.

In some instances this information has made the difference between minor component repairs and major engine overhauls. Often there is a distinct correlation between contamination or additive depletion and increased wear metal content, making it relatively easy to not only isolate the problem, but recommend specific action as well. Analytical techniques include atomic absorption, emission spectroscopy and Ferrographic analysis, with each technique offering a slightly different perspective on wear metals.

Industrial Hydraulic Fluids
Periodic analysis of industrial hydraulic fluid is an important element in extending useful life, ot only of the fluid itself, but of the hydraulic components as well. Early detection of fluid degradation or contamination can greatly reduce the damage from corrosive acids, water or particulate matter. This means longer component life, reduced equipment downtime and greater production efficiency. An effective hydraulic fluid analysis program should include the following tests:

Viscosity -- One measure of the degradation of a hydraulic fluid is its viscosity, often measured in Saybolt Universal Seconds (SUS). As petroleum based hydraulic fluids bread down, their viscosity increases. Normally a 10% increase in viscosity is a warning that the fluid is reaching the end of its useful life and should be scheduled for a change-out. In most cases the viscosity should increase slowly over the life of the fluid, and at a bulk system temperature less than 150 deg. F, this should be thousands of service hours. A more rapid increase in viscosity can indicate a cooling system failure or an unexpected hot spot in the system. Viscosity can decrease if there is fuel dilution or contamination from a lower viscosity oil so it is best to also look at the acidity and specific gravity to determine the level of degradation.

Acidity -- Another measure of degradation is acidity, measured as milligrams of potassium hydroxide needed to neutralize a gram of sample (mgKOH/gm). As hydraulic fluids break down they generally form acidic byproducts which can be corrosive to metal components. The greater the fluid degradation, the greater the level of corrosive acids and the greater the danger of component failure. Some hydraulic fluids have additives which are themselves acidic, so the most meaningful measure is the change in acidity from new fluid. you can determine the new fluid acidity by checking the product data sheets, or have a sample of new fluid analyzed just after system change-out. A change of more than 1.0 mgKOH/gm in acidity is a warning that6 degradation is increasing.

Water Content -- One of the greatest threats to a hydraulic system is water contamination. water is not only a poor lubricant, but it also promotes metal corrosion. Most petroleum hydraulic fluids will dissolve less than 1% water, and a good warning point is a level of 0.2%. At higher levels there is a tendency for water to collect in vapor areas of the system such as relief valves or other control valves that are not used on a regular basis. In some cases these can rust completely and will not function properly when actuated. Water contamination can be detected visually because it gives a milky white appearance to the fluid. A more accurate measurement of the percent water content can be made with any one of a number of common laboratory tests.

Particle Count -- Another measure of contamination is the particle count. A 100 ml sample of fluid is analyzed to determine how many particles are present in different size ranges. Particle counting can be done visually through a microscope, or with an electronic particle counter. Small particles (less than 5 microns) are the most damaging in close tolerance areas such as the knifeedges of servovalves, while larger particles can accumulate and restrict flow through filters or small orifices. Large particles are often ingested dirt while smaller particles are often generated by the system itself in the form of wear debris. In either case, high levels of particles are damaging to system components. Their source should be identified and eliminated, and their presence reduced with filtration.