Oil is everywhere in the fabricated metals industry. There are machining oils, cutting fluids, lubricating oils, and greases. Few industries have such a pronounced need to have an oil analysis program that ensures its manufacturing processes and equipment function as designed. Establishing and operating a cost effective oil analysis program that produces real results is driven by planning, and the selection of the appropriate oil analysis technologies. Let's focus on the process of establishing and operating an effective oil analysis program based on contemporary systems thinking in condition based maintenance.

Planning an oil analysis program
The key to success with a program begins with proper planning. Too many well intentioned programs fail from lack of planning. The process begins with an assessment of the current situation. What is currently being done? How is it being done? What have the results been? An objective look at the current situation provides a framework for the steps that follow.

To plan properly, it is necessary to establish a budget. If the funds are not available, planning is futile. Also, you must know what human resources are available for tasks such as taking samples, reviewing test results, making maintenance action recommendations, managing data and information, and administering the program. Oil analysis programs often fail, as do small businesses, from lack of adequate financial and human resources.

After assessing the current situation and allocating resources, the program manager conducts a survey of the operation to determine the specific equipment to be be monitored. The manager creates a list or database of the potential pieces of equipment that could be monitored using oil analysis. The list should be prioritized based on a simple set of criteria:
 

•  the critical nature of the equipment to the manufacturing process or operation,
•  the capital cost of the equipment,
•  the availability of redundant systems, and
•  the cost to repair the equipment.

After identifying the equipment, gather information about each piece. Develop some form of equipment data sheet to capture information for eventual inclusion in a database. This database may be developed and maintained on-site or maintained by the laboratory that supplies the oil analysis service. Information that typically appears on an equipment data sheet includes a description of the equipment, the type of power, coolant, oil filter, lubrication system, shaft speed, shaft motion, service rating, oil change interval, oil temperature, reservoir capacity, lubricant type and manufacturer, and viscosity specifications. The program is enhanced if you gathered specific information about the mechanical and wear components of the equipment, for example, bearing type and metallurgy of the components, gear type and metallurgy, type of pumps, and so forth. The more that is known about the equipment, the more effectively the oil analysis technology diagnoses potential equipment failures. The key is selecting the appropriate oil analysis technologies for the specific equipment being monitored.

Appropriate technologies
Oil analysis falls into two categories, lubricant or used oil analysis that determines the condition of the lubricant and ferrography or wear particle analysis that determines the condition of the equipment.

Lubricant condition testing
Conducting laboratory tests that measure the lubricant's physical properties determines the condition of the lubricant. There are many tests that a laboratory can perform, however, there are a few that are critical to determining the condition of the lubricant. They include the following.

Viscosity is the single most important physical property of any lubricant. In simple terms, viscosity is a measure of the lubricant's ability to flow. Viscosity varies with temperature. The higher the temperature the lower the viscosity. When selecting lubricants for specific applications, viscosity must be given primary consideration.
 

Fourier transform infrared analysis determines the presence of water and coolant contamination and identifies and monitors the depletion of additives, and the buildup of oxidation products.

Total acid number and total base number are titration analyses that measure the level of acidity or alkalinity of a lubricant indicate of the lubricant's condition. An increase in the total acid number may indicate lubricant oxidation or contamination from an acidic byproduct, while a decrease in the total base number may indicate that a lubricant is losing its ability to neutralize acid contamination.

There are several methods for determining water content in a lubricant. The crackle test is a crude--but often reliable--method for determining if there is 500 parts per million or more water in lubricants. The test calls for heating the lubricant on a hot plate to 100 degrees C. If the lubricant crackles, it's probably contaminated with water. A more sophisticated method, using a coulometric Karl Fisher titration, can also be done. This method can detect water to concentrations as low as 10 ppm.

Spectrographic analysis quantifies the amounts of various elements--iron, copper, lead, tin, silicon, potassium, phosphorous, zinc, and so on. Common methods of analysis include atomic absorption, atomic emission spectroscopy, or inductively coupled plasma.

Analysts use atomic emission technology most frequently in lubricant analysis. The technology relies on detecting light emitted by the elements using a rotating disk emission technique. Spectrographic analysis provides information on the concentration of the various elements in parts per million and determines the level of metals, contaminants, or additives in the lubricant. This method can only see dissolved elements or particles that are less than 8 microns. It is not capable of determining the presence of larger wear particles-- 10 to 300 microns. A common misconception is that spectrographic analysis used in lubricant condition analysis provides for the detection of wear metals and wear particles. This is simply not the case.

Equipment condition testing
Often, used oil analysis that determines the condition of the lubricant is used exclusively in an oil analysis program. Used oil analysis cannot give the kind of information needed to determine the condition of monitored equipment. The only technology available in oil analysis that determines the equipment condition is ferrographic wear particle analysis.

Ferrographic wear particle analysis is a machine condition monitoring technology that determines the condition of lubricated equipment. This technology provides insight into the condition of a machine's lubricated components--bearings, gears, pistons, and so on--through the examination of particles entrained in the lubricant. Particle morphology--size, shape, color, surface texture--provides information on types and sources of abnormal component wear in monitored equipment. This technology is common in many industries including the fabricated metals industry to predict impending wear related failures prior to catastrophic loss.
 

A two-stage process
Ferrographic wear particle analysis is a two-stage process. The first stage involves monitoring and trending wear particle concentration using a direct reading. The ferrograph quantifies ferrous wear particles less than 5 microns (Ds) and greater than 5 microns (Dl). The wear particle concentration illustrates the sum of Ds and Dl as a trend for each piece of equipment. An increase in the wear particle analysis provides the earliest possible indication that a machine is experiencing the onset of abnormal wear. This indication triggers the need for analytical ferrography.

Analytical ferrography involves a ferrogram using a ferrogram maker. A prepared sample of lubricant flows down an inclined glass slide that rests on a strong magnet. The magnet attracts ferrous particles in strings perpendicular to the flow. The strings are aligned with the direction of the magnetic field created by the magnet.

Once the slide is made, an analyst reviews it using a three-power bichromatic microscope. Under magnifications of 100X, 500X, and 800X, and both transmitted and reflected light, the analyst distinguishes size, shape, color, and surface texture of ferrous, nonferrous, and nonmetallic wear particles.

There are many types of particles identified using ferrographic wear particle analysis and each one provides important clues as to the nature of normal and abnormal machine wear. The six most common types of particles include the following.

All types of equipment generate normal rubbing wear particles continuously. They consist of flat platelets generally 5-10 microns in size. There is little or no visible texturing of the surface and the thickness is one micron or less.

Cutting wear particles result from one surface penetrating another. These particles are thin to thick curled strips of either ferrous or nonferrous material.

A common misconception is that spectrographic analysis used in
lubricant condition analysis provides for the detection of wear metals and wear
particles. This is simply not the case.

Cutting wear particles arise two ways. First, hard components become misaligned or fractured resulting in a hard, sharp edge penetrating a softer surface. These particles are coarse and large, averaging 2 to 10 microns wide and 25 microns to 100 microns long. Second, abrasive contaminants in the lubricant become embedded in a soft wear surface such as a lead and tin alloy bearing. The abrasive particles protrude from the soft surface and penetrate the opposing wear surface. This generates very fine wire-like particles with thicknesses as low as 0.25 micron. Any signs of cutting wear particles signifies an abnormal situation. The larger widths and the longer lengths is a strong indication of a failure mode in process.

Bearing fatigue cracks generate spherical particles and appear before any actual spalling occurs. Rolling bearing fatigue is not the only source of spherical metallic particles, however. Welding, grinding, or sandblasting processes also generate them. Rolling fatigue generates few spheres over 15 microns in diameter while welding, grinding, and sandblasting generate spheres over 20 microns in diameter. Also, spheres caused by outside contamination processes usually appear coarse and oxidized.

Severe sliding wear particles are an indication of excessive load on surfaces in contact. These particles are long and flat and their sliding striations make them easily identifiable. Severe sliding wear particles are larger than 30 microns and sometimes appear tempered in color due to the extreme temperatures and pressures associated with their production.

The passage of a wear particle through a rolling contact forms bearing wear particles--laminar wear particles. When a particle passes between surfaces of rolling elements, the particle flattens, the edges split, and holes form. A bearing generates laminar particles throughout its life, but at the onset of fatigue spalling the quantity increases. An increasing quantity of bearing wear particles in addition to spherical wear indicates rolling bearing fatigue.

There are two primary mechanisms associated with gear wear-- pitch line fatigue and scuffing or scoring. Particles from a gear pitch line are similar to rolling-element bearing fatigue particles. They usually have a flat surface and irregular shape. These particles result from stresses on the gear surface causing the cracks to spread deeper into the gear tooth prior to spalling. Excessive loads and speed cause scuffing or scoring. These particles tend to have a rough surface and jagged border. Some of the large particles have striations on their surfaces indicating sliding contact.

Equipment specific analysis
The specific monitored equipment dictates the types of tests for both used oil and ferrographic wear particle analysis. The table above lists machines found in the fabricated metals industry and the recommended suite of tests that they require.

Equipment specific recommendations are based on the type of equipment, lubricant, operating environment, and many other factors.

Program benefits
A properly planned and well run oil analysis program provides many financially justifiable benefits, including:
 

•  asset life extension,
•  ensures that the correct lubricants are being used,
•  identifies probable equipment failure,
•  reduces downtime,
•  deduces risk of catastrophic loss,
•  reduces oil change frequencies, and
•  reduces waste disposal costs.

Know what your are getting
When it comes to oil analysis and condition monitoring, make sure that you understand that used oil analysis provides lubricant condition and ferrographic wear particle analysis provides machine condition. You need a combination of both if you plan to run a comprehensive condition monitoring program based on oil analysis.