7/27/2019 Detecting Premature Bearing Failure.doc http://slidepdf.com/reader/full/detecting-premature-bearing-failuredoc 1/71 Detecting Premature Bearing Failure • • • • Eugene MatzanTags: bearing lubrication Bearing manufacturers have long been aware of the relationship of heat to bearing life and have designed formulas to accurately calculate safe operating temperatures. The results show a temperature band in which both bearings and lubricants will operate at peak performance with the least stress. Once outside the ideal temperature range, they will degrade at an accelerated rate. So how do you interpret temperature readings, and how should they affect your maintenance procedures? This article describes some temperature- oriented methods for determining bearing health and life expectancy, both in the plant and in the field. Figure 1. Heat Ranges of Bearings 1 Figure 1 shows the thermal range of a typical rolling element bearing. Note that bearing metal temperature is often higher (10 to 25 degrees Celsius) than the oil temperature in the bearing within an oil circulation system. The green zone represents the sweet spot for bearing and lubrication temperature; operating in the yellow zone reduces lubricant and bearing life; and if your bearings are in the red zone, expect both the bearing and the lubricant to be destroyed rapidly. There are different temperature bands for different combinations of bearing and lubricant, but they will have the same general trend regarding the best operating temperature and its effect on accelerated wear and failure. In most standard lubricants, for every 15°C1 increase in temperature above 70°C, the lubricant life is more than halved and there is a negative effect on bearing life. Any mineral oil operating at a temperature above 80°C or 90°C will have a greatly diminished life. In no case should bearing temperature ever exceed the maximum rating of either the bearing or the lubricant. Monitoring Bearing Condition Machine bearings are generally monitored through vibration analysis, oil analysis and/or ultrasound techniques. Through these, it is possible to compare current data to historical data and accurately assess the life of the bearings. Temperature increase due to increased
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Bearing manufacturers have long been aware of the relationship of heat to bearing life and
have designed formulas to accurately calculate safe operating temperatures. The results
show a temperature band in which both bearings and lubricants will operate at peak
performance with the least stress. Once outside the ideal temperature range, they will
degrade at an accelerated rate. So how do you interpret temperature readings, and how
should they affect your maintenance procedures? This article describes some temperature-
oriented methods for determining bearing health and life expectancy, both in the plant andin the field.
Figure 1. Heat Ranges of Bearings1
Figure 1 shows the thermal range of a typical rolling element bearing. Note that bearing
metal temperature is often higher (10 to 25 degrees Celsius) than the oil temperature in the
bearing within an oil circulation system. The green zone represents the sweet spot for
bearing and lubrication temperature; operating in the yellow zone reduces lubricant and
bearing life; and if your bearings are in the red zone, expect both the bearing and the
lubricant to be destroyed rapidly. There are different temperature bands for different
combinations of bearing and lubricant, but they will have the same general trend regarding
the best operating temperature and its effect on accelerated wear and failure. In most
standard lubricants, for every 15°C1 increase in temperature above 70°C, the lubricant life
is more than halved and there is a negative effect on bearing life. Any mineral oil operatingat a temperature above 80°C or 90°C will have a greatly diminished life. In no case should
bearing temperature ever exceed the maximum rating of either the bearing or the lubricant.
Monitoring Bearing Condition
Machine bearings are generally monitored through vibration analysis, oil analysis and/or
ultrasound techniques. Through these, it is possible to compare current data to historical
data and accurately assess the life of the bearings. Temperature increase due to increased
friction is not even considered as a symptom of bearing failure in many bearing analysis
texts2 until Stage 3 bearing failure occurs.
If temperature is a reliable method of bearing life prediction, why is it ignored until after it's
too late? The monitoring of temperatures with thermography has been considered unreliable
because so many variables such as ambient temperature, speed, load and runtime all havea pronounced influence on bearing temperature. This article compares identical or near-
identical bearings on the same shaft which cancels the effects of these variables because
they are common to both bearings. The remaining temperature differences between the two
bearings on a common shaft with the same load, can only be the result of friction, an
indicator of bearing problems.
Perhaps subtle changes are hidden because there are so many variables that can potentially
contribute to bearing temperature. In addition to friction, other factors that can contribute
to temperature variation are load, speed, ambient environment temperature and runtime
duration. If these conditions could be predicted and accounted for accurately, then increases
in temperature would reliably indicate bearing problems.
In most cases vibration analysis and oil analysis are still the best ways to determine bearing
health. Unfortunately, it's not always possible or affordable to use these methods in hostile
production environments. Any environments where staff or technicians cannot easily access
the machine without taking it offline, or cannot access the machine due to hazardous
conditions or inconvenient locations make vibration or oil analysis expensive at best, or
even impossible. There are many industries and production environments where bearing
failure represents catastrophic loss, yet vibration analysis is not practical. Photographic film
and paper manufacturing, chemical processing and metalworking plants are a few examples
of industries that depend greatly on bearings, but where bearing accessibility can be a
major problem. Most manufacturers have at least some vital equipment in areas that are
not easily accessible.
Infrared Sensors
Outside of manufacturing, other industries are similarly affected. Wheel bearings on railroad
cars are a specific case in point: they are underneath trains, which are not hospitable places
for performing these tests while the cars are moving. Secondly, there is no practical method
of checking all such wheel bearings in a timely manner because of the sheer number of
them in use. Currently in the railroad industry, the only practical method for detecting
impending bearing failure is to use so-called hotbox detectors. These are infrared sensors
located along the train tracks that detect high temperatures in wheel bearings as the trainpasses. These are extremely limited and can detect bearings only in Stage 4 failure where
catastrophic failure (a wheel burn-off) is imminent. An alarm requires immediate emergency
action, disrupts train schedules, and is extremely costly. When these detectors miss bad
bearings or the alarm is not tended to immediately, the resulting wheel burn-off may lead to
a train derailment, widespread hazardous chemical spill, loss or severe damage of client
merchandise, or loss of human life. Because the consequences are so dire, every false
positive results in delays and inspections that can negatively affect the entire industry.
If bearing temperature changes due to maintenance-related problems could be isolated
from all the other factors that contribute to bearing heat, a properly designed monitoring
device could detect bearing failure at the Stage 2 level. A newly patented technique is being
evaluated that could have significant benefit to industries that need to analyze bearing and
lubrication life in difficult-to-reach areas, such as under train cars. The heart of the patent isa technique that cancels all thermal variables except the increase in bearing temperature
due to wear or lubrication failure.
The procedure takes heat data from each bearing on a common shaft and compares the
data. Because the load, speed, ambient temperature, and run duration are common to all
the bearings common to the shaft, their effects on temperature are canceled. Any recorded
temperature variation is the result of unwanted maintenance- or repair-related conditions
such as over- or underlubrication, bearing damage, misalignment, or loose-foot condition. If
one bearing is more than 15°C greater than another on the same shaft, the bearing health
is in question and the root cause of the increased bearing temperature must be determined.
The bearing comparison is accomplished with electronic temperature sensors and
comparators powered by a self-contained power supply that recharges its battery through
the motion of the equipment.
The methodology involves the following:
• Temperature sensors are attached in close proximity to all the bearings on a
common shaft or axle.
• The sensors apply input to a sensing unit that is self-contained and has wireless
technology for communication with warning devices.
• The temperature data of each unit is analyzed and compared electronically.
• If any bearing temperature varies more that 15°C, an alarm is transmitted and an
LED indicator will light.
• The system is self-powered by a small power supply which is actuated by the
movement of the equipment.
• There is a maximum allowable temperature in case all bearings are out of normal
operating range.
This technique will never be as accurate as oil or vibration analysis, but in remote or
hazardous locations where these tools are not an option, it will provide an increased level of
condition monitoring that was not available in the past.
liters per minute to eight turbine bearings from one reservoir. The oil flows from the
reservoir by a single pump and filter, then separates to the eight bearings. We take the oil
samples from the return lines before they join for the return to the reservoir. None of the
samples show much wear. On the last sampling when there was a sign of bearing failure,
the sample for that bearing showed only 4 ppm iron, 2 ppm tin, 1 ppm aluminum, 2 ppm
silicon, 2 ppm sodium, 2 ppm magnesium, and everything else 0. Viscosity was 66.7 on
Regal 68 at 1,000 hours (6,200 on the unit). Why would samples not show that there was a
problem?"
The answer to your question can likely be summed up in one word — dilution! Assuming, as
you state, that you are sampling on the return lines from each bearing, the reason for the
low wear metal levels is likely due to the comparatively high oil volume in the return lines.
In oil analysis, wear debris is measured in parts per million. When you state "2 ppm tin,"
what you are actually saying is "2 mg of tin for every kilogram of oil."
So the same amount of wear debris distributed in a large volume of oil, such as a circulating
turbine, will generate a much lower ppm than the same amount of wear in a small wet
sump system where the volume of oil is typically much smaller.
To minimize the effects, try to ensure the sample is taken as close to the bearings aspossible. In addition, ensure that the sampling method is precisely controlled with the same
method used every time, including flushing volumes. You might also need to tighten your
alarms considerably to the extent where "normal" really means 0 ppm of tin (and other key
elements), and any slight increase (even just 1 to 2 ppm) is considered "cautionary."
Other possible causes of the low wear metal limits could be a failure mechanism, which
really doesn't generate significant amounts of wear debris, or one that creates larger sized
particles (in excess of 5 microns), which do not show up in conventional elemental
spectroscopy techniques. However, given the nature of this application, dilution is the most
likely cause.
While most lubrication teams grasp the importance of good oil sampling, they are not
exactly sure how to address the specifics. The good news is that instituting a quality oilsampling program in a plant is generally a relatively inexpensive exercise with high, short-
term paybacks. If you haven’t instituted a world-class oil sampling program, now is a good
time to start. If a sampling program is in place, maybe now is the right time to review it for
compatibility with reliability goals. Don’t let a poor oil sampling program shoot your oil
analysis program from the sky.
Mapping Oil Pressure to MeasureBearing Wear
••
•
• Gary Blevins, Wearcheck Africa Dan Burger, Wearcheck Africa Tags: bearing lubrication
One of the buzzwords used in regard to condition monitoring is oil pressure mapping. This
article explains oil pressure mapping, why this diagnostic technique was developed and how
it is used to measure engine bearing wear.
Testing for Bearing Wear
Traditionally, testing for abnormal wear or damage to the main or big end bearings was
carried out by measuring engine oil pressure at idle and maximum engine speeds. The
reasoning was that excessive bearing clearance would cause excessive oil leakage and a
resulting drop in oil pressure.
This test is no longer reliable as modern diesel engines are fitted with high-capacity oil
pumps, which are needed to deliver oil to the spray jets used to cool the pistons. As a
result, the pumps can cope with higher oil leakage rates, so there is little noticeable drop-off
in oil pressure. This is why oil pressure mapping is used.
Before discussing oil mapping in more detail, it’s helpful to take an in-depth look at
bearings, their importance in maintaining healthy equipment, and why oil pressure affects
bearing wear.
Bearings and Oil
A bearing is often an inexpensive part in a machine, but the failure of a bearing results in aconsiderable amount of consequential damage to other components. It is for this reason
that maintenance personnel are concerned about the health of bearings.
Oil analysis is an important tool used to assess the soundness of a bearing. Once a problem
is detected through oil analysis, it must be investigated to establish the cause and extent of
the problem.
The following are a few of the common causes of bearing faults:
• overloading or shock loading
• contamination of lubricating oil
• overheating of lubricating oil
• overheating of the bearing
• misalignment or incorrect assembly of the bearing
• insufficient pressure and/or volume of the lubricating oil
The secret to long bearing life, after installation and operational problems have been
corrected, is to ensure that the bearing is supplied with the correct grade of oil in sufficient
quantities, and that the oil is clean and runs at the correct temperature.
Plain bearings, in particular, are sensitive to oil volume and pressure. Insufficient pressure
will normally result in insufficient oil volume being delivered to the bearing. The decreased
oil volume causes the bearing to wear out faster, due to increased operating temperatures
and contact between the journal and bearing.
Antifriction (roller or ball-type) bearings can normally run on relatively small volumes of oil.
However, a drop-off in oil volume will cause wear on the cage due to the increased sliding
contact in this area. The wear then allows the rollers or balls to move out of position and
accelerate wear of the bearing races.
Oil Mapping
An oil pump, like most other pumps, produces a rapid increase in output as speed increases
until a critical point is reached, after which the output drops off again.
To prevent erosion damage to the bearing from the excessively high oil pressures possible
with the high-capacity oil pumps fitted to modern diesel engines, a pressure-relief valve is
Any change or drop-off in the graphs should be investigated. First, check the pump and
pressure-relief valve. If no fault is found with the pump, the engine itself should be
inspected for excessive leakage.
Engines Fitted with Scavenge Pumps
Engines on some earthmoving equipment are designed for operating on slopes and arefitted with scavenge pumps. It is generally not possible to check the function of the
scavenge pump. It tends to wear out faster than the main pump due to oil aeration in the
scavenge pump when the engine is running level. An undetected scavenge pump failure will
soon result in bearing failure. Engines fitted with this type of pump must have the pump
stripped and checked for damage at planned intervals of at least every 10,000 hours of
If you regularly read this column, you have likely seen my articles on grease application and
selection. In the past, I have focused on manual grease application. For this issue, I decided
to offer opinions on the topic of automatic grease application - specifically, single-pointautomatic grease applicators.
There are two primary reasons to select automatic application: improved quality of
lubrication and/or reducing man-hour requirements for grease application. Like most other
lubrication methods, the successful use of single-point grease applicators requires some
knowledge of lubrication fundamentals; many common mistakes are made. In order to get
positive results from such devices, you must select the right type of applicator for a given
application, install the device correctly and determine the optimum application rate.
Comparing Methods
There are certainly advantages to automatic application when compared to manualapplication. Theoretically, it is preferable to apply small amounts of grease at short intervals
rather than large amounts of grease at long intervals.
With manual application, the trick is to apply as much grease as possible without causing
harm due to over-greasing, thereby maximizing the relubrication interval. While this is fine
for most grease-lubricated components, there are many applications that may benefit from
more frequent application or could be harmed by large application volumes. Of course, you
centralized grease systems and the benefits they offer, the various types, concerns to watch
out for and tips on how to maintain them properly.
Advantages of Centralized Grease Lubrication Systems
Centralized grease systems are designed principally to make the work environment safer for
maintenance personnel by simplifying the process of accessing remote grease points,especially in confined spaces, when equipment is in operation. However, the primary benefit
is derived from the continuous application of small amounts of grease resulting in improved
equipment life, due to the uniform supply of grease.
Hand application is typically performed infrequently and may result in uneven amounts of
grease being applied, which can lead to overgreasing resulting in damaged seals and
elevated bearing temperatures caused by grease churn.
It is important for maintenance professionals to realize that many centralized grease
systems have long lines, precise metering valves, fittings and numerous connections that
can malfunction due to vibration, air entrainment and other environmental impacts. Thus,
carefully monitoring and maintaining the systems on a consistent basis is critical.
Types of Centralized Grease Systems
Centralized grease lubrication systems are designed to lubricate the broadest range of
stationary and mobile equipment. As the lubrication application becomes more complex, the
design of the system also becomes more complex as additional features are added.
Most centralized grease systems fall into two categories. The first is a direct system in which
a pump is used to pressurize the grease and meter it out to the application point. The
second and more complex type is an indirect system in which a pump pressurizes the
grease. Valves built into the distribution line are then utilized to meter the grease into the
bearings.
Indirect systems are further broken down into two basic types, parallel and nonparallel. In
parallel systems, also known as nonprogressive, the system is pressurized and the metering
valves operate simultaneously. The disadvantage of a parallel system is that it can be
difficult to identify a failed (blocked) valve, as grease will continue to be dispensed through
the remaining valves. Pump pressure will not increase and there will be no outward sign of a
injectors represent the key to quality performance. In single-line systems, injectors are
responsible for metering the correct amount of grease to the bearing or other surfaces
requiring grease lubrication. When advancing to a new cycle, one must always vent the
injectors.
The other type of system, the dual- or two-line system, uses two supply lines to providegrease to the injectors. A four-way valve is used to direct grease alternately to each of the
grease lines while relieving pressure on the other line. The second line provides a safety
margin but involves additional cost and complexity related to installation.
There are a number of ways to control both the single- and dual-line systems. The valves
can be operated manually, cycled by a timer or controlled by a counter that measures
grease flow.
Various strainers, filters, alarms and monitoring devices may also be included in the system.
These systems are set up in one, two or three stages, depending on the number of
lubrication points.
Besides injector valves, all centralized grease lubrication systems incorporate a reservoir of
grease, pump, controller, lines and metering blocks as shown in Figure 1.
A constant-level oiler is used to maintain the fluid level in a piece of equipment that
naturally depletes fluid through use, wear, friction, misting or evaporation.
As oil is depleted in equipment, such as bearings, gearboxes, pillow blocks or pump
housings due to its natural operation and the generation of heat from friction, the level of
fluid changes. A constant-level oiler can be used to maintain optimum performance.
The operation is based on the liquid seal principle: as fluid is depleted in the equipment, the
liquid seal on the spout inside the constant-level oiler is broken. When this occurs, air enters
into the oil reservoir from the air vent. This releases the fluid from the reservoir and allows
it to flow into the equipment until the liquid seal reestablishes itself.
An automatic constant-level oiler can be used for antifriction, sleeve, roller, ball, tapered,
spherical or slinger bearings involving excessive backpressure. Applications include fans,
motors, blowers, gearboxes or other equipment where a constant level of fluid needs to be
maintained. Constant-level oilers are most useful in paper mills, cement plants, coal
handling mills or industries with similarly dirty environments, because the sumps are
opened less frequently.
Basic Design and Operation
In situations where pressure or a vacuum is generated in the sump, it is preferable to
provide a vent line back to the equipment housing above the oil level to equalize thepressure. By equalizing the pressure between the oiler and the equipment (Figure 1), the
level is more accurately maintained, creating a closed-loop system. In the event that there
is no place to pipe the air vent back to the equipment, a filtered vent plug at the reservoir
can be used to prevent environmental contaminants from entering the system. Figures 2
and 3 show the two fluid connection points, of which either point can be used for installation
or drain. One is located on the side of the housing while the other one is on the bottom.
If we assume the technician is satisfied with two strokes (if he doesn’t see any grease
coming out of the seals), then after a year the bearing will receive 156 grams (52 weeks
times 3 grams per week) instead of 104 grams (52 weeks times 2 grams per week). Thismeans that up to 52 grams (50 percent) of grease will be wasted.
This example shows the benefit of accurately delivering the right quantity of lubricant (the
second “R”), but what about the frequency of lubrication (the third “R”)?
Extending relubrication intervals beyond the calculated limits will expose the lubricant to
excessive degradation and the bearing to lubricant starvation conditions. On the contrary,
shortened relubrication intervals with adjusted quantities would renew the lubricant’s
properties.
To illustrate this point, consider that on average, a human being requires about 2,000calories per day. Would you rather consume your weekly total of 14,000 calories once a
Lubricant contamination will also affect bearing life and increase the risk of failure. In
manual lubrication programs, avoiding grease contamination can be a challenge. Processes
must be clean to ensure no external contamination ingress to the grease, and eachlubrication point should have a cap on its grease fitting. In addition, the utmost clean
relubrication process for each point must be followed every time.
In the previous example, the technician will relubricate the given point 52 times a year. As a
result, the bearing will be exposed 52 times to external contamination as well as to over-
and under-lubrication. By comparison, a properly installed single-point automatic lubricator
can supply a continuous and accurate flow of fresh and clean lubricant, keeping the
application in proper condition while at the same time preventing contaminant ingress.
Labor Savings
The simple task of pushing a lever on a grease gun to provide manual lubrication can be
easily replaced by a machine. However, the real issue is whether you are getting the
maximum value from your skilled maintenance technicians. Such personnel can manage a
lubrication program through:
• Continuous improvement of the lubrication routes
• Implementation of a contamination control and oil reconditioning program
• Implementation of a leakage control program
Keep in mind that while deploying automatic lubrication systems can free personnel from
time-consuming basic activities to provide extra value, it cannot replace staff who can
deliver value at this level.
Environmental Health and Safety
Improper relubrication activities can have a significant impact on the environment. Consider
again the grease waste calculations in the previous example. Now try to estimate the impact
of this waste on the environment. Naturally, it depends on the disposal practices you
implement at your facilities, but in basic environmental terms, the less waste the better.
Next, consider points that are difficult or even hazardous to access and the potential impact
to your personnel. This is another area where automatic lubrication systems offer real
benefits.
Common Problems
Simply using automation doesn’t guarantee success. The technology must be considered an
instrument to achieve a goal. Basic decisions and activities must still be performed. The
following are typical mistakes that can jeopardize the potential benefits of deploying
automatic lubrication.
Lack of Inspections
Having an automatic lubrication device doesn’t mean that the system won’t require any
inspection. Regular inspection will help ensure the best results from an automated system.
Inspection also will help to identify installation issues (damaged fittings, leaking or blocked
pipes, lubricators not dispensing at the right pace, etc.) and spot when it’s time to change
or refill lubricants.
Moreover, lubrication routes must be updated, and manual lubrication tasks must be
replaced with inspection tasks at an adequate interval. The frequency of inspection is lessthan that required for manual relubrication, but it still must be planned.
Improper Lubricant Selection
As a fundamental in any lubrication program, the lubricant selection must precede the
lubrication system selection. After all, the lubricant that goes into the application is what
The lubricant and the automatic lubrication device must complement each other to ensure a
better overall performance. Needless to say, not all lubricants are suitable for all automatic
lubrication systems, and the impact of a lubrication system on the structure of the lubricant
depends on the technology of that given lubrication system.
Consequently, parameters like pumpability and oil separation must be taken into accountwhen an automatic lubrication system is to be installed. Furthermore, relubrication intervals
must be defined in a way that prevents the lubricant from being stationary inside the
lubrication ducts, especially when exposed to extreme temperatures that could promote
premature degradation. Failure to understand and act on these issues can affect the
performance and associated benefits of deploying an automatic lubrication system.
Investment Costs
Of course, deploying an automatic lubrication system requires some level of investment. To
maximize the return on that investment, the key is to choose the right solution based on
the requirements and criticality of the application. Typical solutions range from inexpensive
single-point automatic lubricators to very complex centralized systems with various options
for online monitoring. Determining which option is best for your application depends to a
great extent on your criticality analysis.
When to Use Automatic Lubrication
Automatic lubrication alone certainly is not the solution to all your lubrication issues. It must
be properly understood to boost its potential benefits. However, there are solutions
available in the market for virtually every application, so it is difficult to imagine that a
critical application is not worth equipping with an automatic lubrication device.
Perhaps some of the most abundant components industry wide are bearings, more
specifically rolling element bearings. These bearings are found in everything from electricmotors to gearboxes and conveyor systems. Basically, if a shaft needs to spin, it can be
(and most of the time is) supported by a rolling element bearing. What some people fail to
realize is the actual makeup of these devices can be quite different based on the application.
Rolling element bearings are composed of two races separated by a group of rollers. The
shape of these rollers determines the load a particular bearing can hold as well as the
lubrication requirements.
The first type of roller we will discuss is one of the more common types - the ball bearing.
Ball bearings come in as many sizes, materials and finishes as can be imagined. This
provides incredible flexibility in their use. The balls in these bearings simply roll between the
two races, and it doesn’t matter which direction the elements are facing.
As their name suggests, cylindrical roller bearings are cylinders that are arranged between
the inner and outer races. These cylinders, which are shaped like soda cans, roll along their
sides in the tracks of the races. The elements can only roll along a single axis, unlike balls
Oils have a property known as the pressure-viscosity coefficient. This is a measure of how
well they can momentarily turn into a solid. Water does not have this property and thus can
lead to boundary conditions when it is present in rolling element bearings. It is important to
monitor water levels in the lube oil to keep this from occurring. In some cases, bearings can
lose 70 percent of their life because of water before the oil even gets cloudy.
58%
of lubrication professionals use ball bearings
at their plant, based on survey results from
machinerylubrication.com
There are two types of loads that bearings undergo: radial loads and thrust loads. Radial
loads are experienced as shear forces. These loads occur across the races of the bearing, as
opposed to thrust loads, which are forces that push into the face of a bearing. In other
words, the radial load of an electric motor would be found by any load pushing the shaft of
the motor up or down, while the thrust load would be any load pushing the shaft back into
the motor. The amount and type of loads your bearing is experiencing determine the type of
bearing you need, as well as the rolling elements within it.
Understanding the basics of how rolling element bearings work and their design can helpyou achieve added reliability at your plant. Determining the type of loads you wish the
bearing to handle as well as the ambient conditions will further assist you in the selection of
the proper bearing. The possibilities for bearings are endless, so you can guarantee there is
one that is perfectly suited for your application.
"We are experiencing sleeve bearing failures on a piece
of equipment. The main cause of failure is bearing wear due to mechanical misapplication of
the equipment. We are not in a position to change the bearing type yet because we have to
meet current production demands. Would a simple magnetic plug help to remove 'free'
particles of entrained bearing material and slow down the rate of wear until we can correct
the root cause?”
Unfortunately, magnetic plugs trap only large ferromagnetic wear debris (typically larger
than 100 microns). Non-ferrous particles associated with babbitt used in sleeve bearings
would not be removed, nor would ferrous particles (shaft metal, for instance) smaller than
100 microns.
Therefore, wear metal is unlikely to be trapped by a magnetic plug. Instead, try the
following:
- Fitting a couple of quick connects to the bearing housing (top and bottom) would allow a
small portable filtering unit to clean up the oil very rapidly. On the assumption that you
would need to turn over the volume seven times, a 5-liter-per-minute pump would take less
than 10 minutes to clean up the oil to a very clean level. In conjunction with the new
breather unit, this would minimize the main cause of wear.
- Upgrade the breather/vent units if these are fitted. Bear in mind that a 10-micron particle
entering through a vent plug is like a snooker/pool ball rolling through a doorway — there islittle chance of stopping it. A good breather will help ensure that no additional
contamination is entering.
- If the machine is being stressed, oil temperatures are probably higher. The OEM-specified
oil may be too thin at the higher temperatures. Consider a change of lubricant viscosity
specification, perhaps even to a multi-grade or synthetic.
iron count was high, about 30, yet the particle count was fairly clean at 17/14. I would
expect the iron count to be low if the system was clean. Can you offer any insight into what
we are seeing?"
In a mission-critical hydraulic system, an X/17/14 cleanliness level may not be all thatdesirable. When looking at a scale for average hydraulic system cleanliness, a level such as
this is borderline between clean and dirty. Generally, a cleanliness level of 16/14/11 or
better would be recommended for this type of application.
You mention a cleanliness level of 17/14. This provides the cleanliness at the greater than 6
micron and greater than 14 micron levels (assuming ISO 11171 calibration). If the
spectrometer is showing 30 ppm of iron, we know this is measuring particles less than 5
microns due to the inherent limitation of this test. Do you have a cleanliness level for the
greater than 4 micron level?
You would also expect the iron count to be low if the system is clean ... provided there areno mechanical conditions that would create iron debris as a leading indicator.
It is possible for a system to be "clean" of environmental and external contamination and
still show wear. In fact, this is what we'd prefer to see. Then we can focus our attention on
repairing the mechanical problem right away rather than dealing with external
contamination control just to find a mechanical problem shortly thereafter.
in Minneapolis, we attempted to start the engine of a dozer that had been sitting outside for
several days. Since last running the engine, outside temperatures had slowly dropped to
around minus 13 degrees F (minus 25 degrees C). The dozer's motor oil viscosity is SAE 10W-30. The engine cranked slowly but still started. However, the oil pressure was very low
and stayed low. What might have caused this? What risks or damage to the engine can
result?"
The high viscosity of the engine oil did not allow oil pressure to build quickly and may also
have caused the system to go into bypass, thus the low oil pressure. Severe damage can
result to the engine from lack of lubrication, including seizure of main and connecting rod
bearings, piston scuffing/seizure, etc.
One solution to the problem would be better storage of the machine exposed to these
severe low temperatures. Covering the engine with insulating material or raising the entiremachine temperature with space heaters within a tent-type cover before attempting to start
the engine might be an option.
If starting in such low temperatures is expected, using a lower viscosity oil like an SAE 5W-
30 may help. The oil should be replaced before the winter season, not at the time the cold-
viscosity at 40 degrees C. At the same time, our lube supplier is testing samples from the
same system regularly. However, our viscosity numbers are often up to 10 percent different
from the lube suppliers. What are we doing wrong?”
Because the viscosity of an oil is probably its single most important property, it makes
sense to measure viscosity frequently, using onsite test equipment. However, like all onsite
equipment, it’s important to understand how these instruments work and their relative
strengths and weaknesses.
When it comes to viscosity, there are two determinable parameters — absolute and
kinematic viscosity. Kinematic viscosity measures the resistance of an oil to flow and shear
under gravity, such as oil flowing through a funnel. Absolute viscosity, on the other hand,determines an oil’s internal resistance to flow and shear. To visualize absolute viscosity,
imagine the force needed to stir an oil using a metal rod.
The viscosity reported by your lube supplier and oil analysis lab is likely the kinematic
viscosity. There are two main reasons why your onsite measurements may not correlate
directly with the lab data.
First, most onsite test equipment actually measures absolute viscosity, but calculates the
kinematic viscosity by dividing absolute viscosity by density. Because the onsite viscometers
don’t actually measure density but rather estimate it from the oil’s spec sheets, an error can
occur when translating absolute viscosity into kinematic viscosity. The measure of theabsolute viscosity is correct, but because the density of the oil is only estimated, the
conversion to kinematic viscosity can become overstated. Contamination and oxidation,
among other things, can cause a rise in the density of used oil.
Second, if your onsite instrument does not heat the oil to 40 degrees C, and most do not,
you are likely determining the oil’s viscosity at the temperature of the onsite lab (typically in
the 20 to 25 degrees C range), and extrapolating, again using a software algorithm to
An oil's viscosity is measured most commonly by kinematic viscosity and reported in a unit
called the centistoke (cSt). Kinematic viscosity is measured in the time it takes for a specific
volume of oil to flow through a special device called a capillary tube.
Not all oils respond in the same way to a given change in temperature. Many oils contain an
ability to resist changes in viscosity due to a change in temperature. This property isreferred to as the oil's viscosity index or VI. The higher the VI of an oil, the less its viscosity
is altered by temperature changes.
The benefits of oils with a higher VI are:
1. A general increase in viscosity at higher temperatures, which results in lower oil
consumption and less wear.
2. A reduced viscosity at lower temperatures, which will improve starting and lower fuel
consumption.
Another factor in the measurement of viscosity is the ability of an oil to resist shearing orthe "tearing away of one plane of lubricant from another" during the hydrodynamic
lubrication function.
However, under certain conditions, such as shock loads, continuous heavy loading,
extremely high temperatures and/or critically low (thin) viscosity, lubricants may not remain
in their normal hydrodynamic film state.
A condition begins where there is intermittent contact between the wear surfaces. This
intermittent contact is called boundary lubrication, and damage starts to occur. If the
conditions noted above are not corrected immediately and boundary lubrication continues, a
failure due to the lack of an oil film can occur within hours.
Kinematic viscosity, viscosity index and shear stress/shear rate are all factors that should be
taken into account by a lubricant manufacturer when blending lubricating oils, but what
does all this mean to the end user? It means that the viscosity of an oil is the first and most
important consideration when selecting an oil for a specific application.
Remember, for the most effective lubrication, the viscosity must conform to the speed, load
and temperature conditions of the lubricated parts.
"Is there any way to tell if an improper lubricant is
being used without performing an oil analysis or without a part or system failure? We
currently have an oil analysis program in place, but I still find that wrong oils and fluids are
being used from time to time in between the oil analysis."
The most effective way to determine if wrong oil has been used is by oil analysis, by looking
at either a change in viscosity and/or a change in additive concentration, etc. Unless there
is a significant difference in oil type (viscosity, base oil type, additives, etc.) or any dye thatmay be used in the oil or grease, it is unlikely that a sensory inspection is sufficient.
However, your problem probably has little to do with oil analysis but is more of a procedural
issue. The bottom line is that you need to make those who are empowered with
adding/changing oil understand why adding the wrong oil is bad.
The first stage is understanding through education, whether it be formal training or simply
internal training sessions. Secondly, you need to make the process of adding oil as foolproof
as possible. The best way to achieve this is to practice lube tagging. In this approach, new
oils are tagged with a designated color and shape. For example, ISO VG 220 gear oil is
given a red circle, AW 46 hydraulic fluid a green square, etc.
The next step is to similarly label dedicated oil transfer equipment such as oil top-off
containers, funnels, filter carts, etc.
Finally, label the gearboxes, etc., with the same red circle, green square, etc. The strategy
is simple: Red-circle oil gets added to red-circle components using red-circle hardware. This
can be applied to all components and hardware, including greases, grease guns, etc.
A good example of lube tagging occurred at the General Motors Linden Assembly Plant in
New Jersey. Management addressed the need to coordinate the equipment requirements
with the labeling of lubricant storage and delivery containers. It created a coding system
that used words, images and colors to define the specific product for each application. Once
identified, the products were then matched with the correct storage and transfer container.
The result was a visual system that clearly communicated which lubricant the machine
required and which container held that particular lubricant. The technician or mechanic
needed no special knowledge to use the simple matching system.
Existing Methods for Analyzing LubricantDispersancy
To date, no rigorous analytical method makes possible the measurement of the dispersancy
capacity of the lubricant. The blotter spot method could provide an answer to this need, butthe only method practiced to date is based on a visual evaluation. This subjective visual
interpretation is not rigorous and consequently limits the information that could be provided
by the method.
Engine Test
The objective of the engine test (DV4TD – CEC-L-93-04) is to evaluate the effect of
combustion soot on engine oil viscosity increase and piston cleanliness. This procedure
simulates high-speed highway service in a diesel-powered passenger car. The procedure
fixture is an engine dynamometer procedure stand with a Peugeot DV4TD/L4 four-cylinder,in-line, common rail diesel engine installed. Pistons and rings are future rated for lacquer
deposits and ring sticking. Kinematic viscosity at 100 degrees C, soot content and iron
content in the used oil are evaluated at 24-hour intervals during the procedure. The final oil
drain is used in conjunction with the intermediate samples to interpolate the absolute
viscosity increase at 6 percent soot.
This approach has the merit of exactly reproducing the behavior of the lubricant under
definite conditions of the test. However, the evaluation methods on the engine are very long
and expensive. In addition, the precision of this test is not at the level of a laboratory
method.
Blotter Test Method
Several versions of this old method exist in industry. Many studies show the value of this
method as being rich in practical information on in-service lubricants, but it remains mainly
manual and homemade. The interpretation of the blotter spot continues to be subjective
and not formalized by a universally recognized method.
To conduct the test, a small quantity of a homogenized sample is heated to 240 degrees C
(464 degrees F) for 5 minutes. The purpose of this short period of intense heating is to
stress any oil that is close to thermal or oxidative failure so that the blotter spot shows apositive response. Any oil that is still in good shape will not be affected by such a short
heating period, which will be reflected in the dispersion pattern of the blotter spot.
obtained between various laboratories. Moreover, with the introduction of new oils and fuels
(e.g., biodiesel, ethanol, etc.), the appearance of multiple rings caused by various pollutants
(carbon particles, etc.) is noted. For these reasons, the visual/manual interpretation of the
various rings is very complicated and not easily exploitable.
There exists an automated apparatus that facilitates the interpretation of the spot andeliminates the subjective aspect from the manual method. This instrument is equipped with
a monochromic charge coupled device (CCD) camera and does not use the information color
of the spot or differentiate each ring of the spot. The apparatus compares the diameter of
the spot with a theoretical diameter and analyzes the opacity homogeneity of the spot. Of
these two parameters, the device calculates a dispersancy index that varies from 0 to 100
(with 100 being the ideal dispersancy).
A New Approach
The goal of this new approach was not to reinvent the blotter test. A computer is used withdedicated software that was specifically developed for recognition and analysis of color
images. With the digital imaging analysis of the spot, in particular its opacity and its
spreading out by means of a dedicated algorithm and the choice of perfectly adapted filter
paper, it becomes possible to evaluate in an objective and quantified way the residual power
of a lubricant to disperse insoluble matter.
The general principle of the method for the preparation of the spot remains virtually
unchanged. It consists of depositing a volume of 15 microliters of oil on a specific filter
paper and analyzing the rings of the spot, which are representative of the dispersion of the
pollutants. The sample volume was decreased from 20 microliters to 15 microliters to limit
the size of the spot and to make it compatible with the image-analysis system, as well as tobe able to analyze all types of lubricants.
The deposit of the oil on the filter paper is carried out at room temperature or in certain
cases at 200 degrees C in order to free itself from the viscosity of the sample. The filter
paper is then placed in a drying oven at 100 degrees C for 24 hours.
The instrument used for this new approach features a light source positioned above the
measurement table (direct light) and a color CCD camera equipped with a high resolution. It
also has dedicated software that is capable of monitoring both the light source and the
camera. The software memorizes the numeric color picture of the spot.
This instrument makes it possible to take a digital color picture of the spot as the human
eye sees it but with higher resolution. The image is memorized for the treatment and added
to the test report, which enables you to visually check the results reported by the software.
The use of a color camera allows you to identify the various rings by obtaining chromatic
In order to analyze the spot under the same conditions of lighting for optimized
reproducibility, the calibration of the device is carried out on a white sheet of filter paper.
The software reports the following data:
•The color image of the spot as the human eye perceives it.
• The digital model in levels of gray associated with an opacity of the delimited ring by
its real form.
• The number of rings present in the spot, with ring 1 being the last external ring.
• The diameter of each ring.
• The surface of each ring.
• The average opacity of each ring.
The software was designed to be able to analyze a series of spots coming from the same oilat various stages of degradation. This possibility was created in order to carry out a follow-
up of each value measured during artificial life tests and also during the engine follow-up.
The new approach makes it possible to obtain results of dispersancy analysis in a numeric
format. With this technique, the detection of the rings is much more precise and repeatable.
Case Study #1: Thermal Qualification of an
Engine Oil
Before testing the new method on lubricants contaminated by biofuel, two lubricants
considered internal references were tested.
• RH 2010 engine oil was qualified as a high-level reference.
• RL 2010 engine oil was qualified as a low-level reference (judged as “borderline”).
For the evaluation of the thermal behavior of engine oil, new and pure engine oil was
stressed with an accelerated aging, including a thermal stress (170 degrees C) in the
presence of oxygen and an oxidation proprietary catalyst. After 72, 96, 120 and 144 hours,
samples were taken. Each sample was then analyzed with the new method and instrument
described previously.
A spreading out of the high-level reference oil RH2010 in comparison to the borderline oil
RL2010 was observed. In addition, it was noticed that opacities of the central rings were
much darker. These tests carried out with the new blotter test method confirmed the
respective quality level of the two engine oils. In this particular case, their capacity to
Case Study #2: Thermal Qualification of anEngine Oil in the Presence of Biofuel
The same two qualified engine oils, the high-level reference and the borderline reference,
were stressed with the aging method, but diesel B10 was added starting from 72 hours of the test. Then, the contamination level of diesel B10 was maintained to 10 percent during
the remainder of the test.
A reduction in spreading out and a more important opacity in the presence of biofuel
GOPSA10LUB for the high-level reference oil was observed. The RH2010 oil approached the
rupture limit at the end of the 144 hours, but the total result according to the criteria
remained satisfactory, although the bad dispersancy in the presence of biofuel was
highlighted.
With this engine oil evaluated as borderline, a reduction in spreading out in the presence of
biofuel GOPSA10 was observed. This result becomes critical with respect to the acceptable
requirements that are based over the duration of 120 hours.
Conclusion
Although a relevant mathematical model must still be developed, this new method will make
it possible to determine the dispersancy of an oil by its capacity to disperse insoluble
matter. It also is able to precisely evaluate the resistance of a new oil to disperse insoluble
matter when submitted to an oxidation test and/or thermal behavior test. In addition, it can
determine the impact of pollutants such as biofuel on the dispersancy capacity of oils thanks
to the precise measurement of each ring.
The process and the instrument of the new method are usable in the laboratory and on
engine benches or rolling vehicles for any mechanical parts lubricated with oil, such as a
marine engine or a wind turbine, and for many types of oils, including industrial oils, cutting
oils, etc. Specific calculation criteria for oils resulting from rolling bench or in-service
vehicles can also be defined.
By analyzing the measured parameters in each ring, it should be possible to determine the
types of pollutants present in the oil and their implication on dispersancy. Thus, it becomes
possible to have an indication on the cleanliness of the bodies and to quantify in a precise
way the pollutants in oil (soot resulting from the combustion of the fuel, metal particles due
to the wear and corrosion of the bodies, products resulting from the aging of oil, etc.).
This illustration shows how particles cause damage
to parts in contact. (Ref. Triple-R Oil Cleaner)
The Sampler
The main concern of the sampler is to produce a homogenous sample that is representative
of the bulk volume of oil in the system. The presence of particles complicates the task of the
sampler, as particles tend to settle at the bottom of the tank/sump.
Prior to sampling, oil should be hot and well agitated to ensure that the sample includes
particles that have settled. For routine oil analysis, the container must not be filled morethan 80 percent to enable the laboratory to agitate the sample prior to analysis.
Improper sample handling includes overfilling containers, decanting samples that were
originally filled to the top and sampling when the oil has not been circulated sufficiently prior
to sampling. Overfilling a container leads to insufficient agitation. Shaking the container
prior to decanting will result in large particles remaining at the bottom of the container.
There’s also the possibility that the less contaminated portion is decanted, causing the
Once the samples reach the laboratory, the presence of particles directs the tasks and
methods that the chemical analyst will use to analyze the samples. The method of sample
preparation, the analytical techniques and instrumentation required to ensure that the
results are representative of the condition existing in the application all depend on the type,
size, properties and distribution of the particles present in the samples.
Various analytical techniques, including inductively coupled plasma (ICP) spectrometers, theflow cell of Fourier transform infrared (FTIR) spectrometers and some particle counters, rely
on peristaltic pumps and transport systems (tubing) to introduce samples to the various
instruments. When large particles are present in samples, the possibility exists that the
Analysts also must be aware of the tendency of particles to settle at the bottom of the
container. Prior to each analysis, samples should be agitated sufficiently to ensure a
homogenous state. Lowering of the fluid’s viscosity either due to fuel dilution in the engine
or dilution due to analytical requirements (e.g., ICP) aggravates the tendency of particles to
settle. With ICP analysis, the samples must be diluted to assist with the transportation
process. Due to dilution, suspended particles are more prone to settle out on the bottom of
the test tube and will not be available for analysis. However, no dilution is required with
rotating disk electrode (RDE) analysis.
The Diagnostician
Particles can be of value to a diagnostician who studies the shape and nature of particlesfound in a sample. A scanning electron microscope (SEM) can assist in investigating the root
cause of mechanical failure by allowing the diagnostician to pay special attention to
evidence such as scratch marks on particles and methods of particle formation.
Fine filtration is a proactive process aimed at removing contamination and wear particles
from the system. If this process is not executed with special care, knowledge and sensitivity
to the value that particles add for the diagnostician in root-cause analysis, crucial evidence
can be lost.
Case Study #1: RDE vs. ICP SpectrometryIn 2002 the Eskom laboratory changed from ICP to RDE spectrometry to perform wear
metal analysis on used oils. To obtain a new baseline, it was essential to perform both
spectrometric methods as well as the ferrous particle quantifier (PQ) on all samples received
for a three-month period.
When the spectrometric results were plotted against the PQ values, it was determined that
the higher the PQ value was for a sample, the greater the difference between the ICP and
RDE results. For a PQ value of 15 milligrams of iron per liter (mg/l Fe), the expected
difference between the two techniques was about 0 to 5 ppm. However, above a PQ value of
approximately 75 mg/l Fe, the relation seemed to become non-linear, where the differences
between ICP and RDE results were from 50 to more than 500 ppm.
As soon as the vibration problem was eliminated, scratching noises were audible. Everything
was checked, yet the source of this noise could not be traced. The maintenance engineer
decided to involve the laboratory that performed the oil monitoring program in the
investigation.
Since the engine was recently refurbished and the original source was unknown, thelaboratory had no history on which to base the diagnosis. To obtain more knowledge about
the solid content of the oil sample, the lab employed specialized methods, such as the
electron diffraction X-ray (EDX) scan technique using the SEM.
To find out if the noise was due to insufficient lubrication, the laboratory determined the
oil’s viscosity. This was to establish if metal-to-metal contact had occurred as a result of the
oil being too thin. A new oil sample of the specified lubricant was submitted for comparison
with the oil sample taken from the engine.
A PQ analysis was then conducted to determine the magnetic property of the oil, followed
by spectrometric elemental analysis using RDE spectrometry. An EDX scan using the SEM
was performed on particles caught after the sample was filtered through a 0.8-micron-filter
membrane and rinsed with pentane to remove oil residue.
The results revealed that the viscosity was acceptable when compared to that of the
reference sample, while the PQ values were very high (more than 1,000 mg/l Fe). The RDE
spectrometric analysis indicated an increase in copper, iron and zinc when compared to that
of the reference sample.
The EDX scan using the SEM found the following components on the filter:
• High occurrence of white metal bearing material
• Metal frets
• Iron, lead and copper shavings with scratch marks
The available ionization energy to energize large particles reaches a plateau, which is one of
the reasons different spectrometric methods have limitations concerning particle size (3
microns maximum for ICP and 8 to 10 microns maximum for an RDE spectrometer).
Spectrometers, as they are applied today, are blind to large particles. Traditional methods
of determining large particles (larger than 10 microns) are acid digestion (expensive andhazardous), microwave digestion (expensive and time consuming) and direct ferrography
(does not include non-ferrous metals).
Rotrode filter spectroscopy (RFS) was developed to provide an improved spectroscopic
method for analysis of used oils for condition monitoring/predictive maintenance without the
particle size or metal-type limitations of previous combined spectrochemical and direct
ferrographic techniques.
Particles as Enemies
Special evidence, such as the scratch marks on the metal frets, suggested that uneven
objects (particles) were responsible for abnormal wear of the liner and/or the crankshaft.
The piece of silicone found indicated overuse of a silicone-containing substance like a
sealant, which possibly was squeezed out between parts, cured and ripped off by the hot
flowing oil. These silicone pieces could have blocked oil passages, resulting in a damaging
situation of oil starvation.
Particles including silicon (quartz) and sand (aluminum silicate) as well as other debris
discovered in the oil sample were responsible for the abnormally high wear. Since abrasive
wear was the main cause of premature aging and resulted in severe damage to the parts in
contact with these objects, the maintenance engineer wanted the reason for the initialingress of those particles into the system to be investigated.
For the sampler, it was essential to ensure that as much evidence as possible was captured
in the drawn sample. In this case, where the ultimate failure would have been catastrophic,
the task could have been quite difficult, since all particles had settled to the bottom as the
oil cooled. Thus, a typical sample drawn in the normal fashion may not have allowed all the
evidence to be captured.
Particles as Friends
By unlocking the treasure of evidence that was captured in the particles found in the oil, the
diagnostician obtained information about the formation of such particles. The presence of
metal shavings indicated possible misalignment. Lack of lubrication also was detected,
which possibly was due to blocked oil channels resulting from the presence of foreign
particles. The metallic iron shaving with lead bound to it suggested welding due to oil
The fleet owner decided to stop the locomotive to find out whether the alerts issued by the
first laboratory were justified. It was discovered that the wrist pin bearing had failed with
damage to four power packs. An investigation was launched to determine the root cause
that resulted in the different diagnoses from the two laboratories.
Routine oil monitoring tests were performed, including spectrometric analysis using RDEspectrometry and PQ. An EDX analysis using the SEM on the filter debris was conducted
after the sample was filtered through a 0.8-micron-filter membrane and rinsed with pentane
to remove oil residue. The results of the RDE spectrometric analysis revealed an increase in
silver, copper and iron, while the SEM analysis confirmed the presence of particles larger
than 10 microns.
Since both laboratories performed similar analysis on a routine basis, the investigation
focused on the differences in the techniques used by the two labs. The only major difference
found was that the laboratories employed different spectrometric techniques to determine
the wear metal content of the samples, namely ICP and RDE spectrometry.
Since no abnormalities were found except for fuel dilution over a prolonged period, the
investigation focused on sampling intervals and techniques that could have affected the
results.
Routine oil monitoring tests, including spectrometric analysis using RDE spectrometry, were
performed, as well as EDX analysis using the SEM on the filter debris after the sample wasfiltered through a 0.8-micron-filter membrane and rinsed with pentane to remove oil
residue.
The results showed severe fuel dilution. The RDE spectrometry indicated no increase in
metal content since the previous sample was analyzed. The EDX analysis revealed that
isolated large particles (larger than 20 microns) of heavy metals and other inorganic oxides
were present on the filter. Many of the larger particles were iron or iron oxides. The small
These photos of a locomotive engine indicate a severely scored liner and piston wear.
Lowering of the fluid’s viscosity, which may have resulted from fuel dilution in the engine,
aggravated the tendency of particles to settle. Therefore, it is possible that suspended
particles had settled to the bottom of the sump and were not included in the sample.
In the earlier stages of failure, smaller particles were produced (likely during the period
when no samples were submitted). As the failure progressed, the size of the particles
increased. Since particles larger than 10 microns were found, it is possible that the failure
progressed beyond the point where the RDE could detect the wear particles. Thus, severefuel dilution over a prolonged period of time combined with not submitting oil samples at
the initial stages of failure resulted in the inability to detect the failure through a routine oil
The trend in the oil analysis world is to give too much credit to the value of the ISO
cleanliness code. Some laboratories have even begun to only report the ISO code. There is
also a heavy reliance on this value by end-user analysts.
The ISO code is a fantastic tool to use for setting target alarms and establishing a goal to
achieve and maintain as it relates to system cleanliness. It is also the perfect value to usefor key performance indicator (KPI) tracking, charting and posting. However, the ISO code
should play only a secondary role when it comes to evaluating used oil sample data.
73%of machinerylubrication.com visitors have
used the ISO cleanliness code to set target
alarms for system cleanliness levels
How the ISO Cleanliness Code is Determined
Most oil analysis samples that receive particle counting are getting what is known asautomatic particle counting (APC). The current calibration standard for APC is ISO 11171.
When sending a sample through an APC, particles are counted either through laser or pore
blockage methods. Although different laboratories may report different particle count micron
levels, an example of the various reported micron levels includes those greater than 4, 6,
ISO 4406:99 is the reporting standard for fluid cleanliness. According to this standard, a
code number is assigned to particle count values derived at three different micron levels:
greater than 4 microns, greater than 6 microns and greater than 14 microns. The ISO code
is assigned based upon Table 1. This can be seen in the example on the left.
However, without seeing the raw data, the only thing the ISO code can positively identify iswhether a sample has achieved the desired target value. The ISO code does nothing to help
determine any type of real trend information unless the value of the raw data at the given
micron levels changes enough to raise or lower the ISO code.
What the ISO Code Can Tell You
It’s easy to look at the ISO table and notice a pattern. At each row, the upper limit for each
code is approximately double that of the lower limit for the same code. Likewise, the upper
and lower limits are double that of the upper and lower limits of the next lower code. This isknown as a Renard’s series table.
The unit of measure for particle count data is “particles per milliliter of sample.” The particle
counters used in laboratories incorporate much more than a milliliter of sample. During the
testing process, approximately 100 milliliters of sample are taken into the instrument. The
numbers of particles are counted based on this value. The total number of particles is then
compared to the number of times that 2 will go into that total count exponentially.
Why is cleanliness so important? The answer is simple: competition. In such a globally
competitive market where products can potentially be manufactured and shipped from
overseas at a lower cost than can be manufactured from here at home, maintaining a
precise level of reliability and uptime is necessary to keep costs at a manageable level.
Contaminant-free lubricants and components will extend the lifetime of both, and in turn
increase the overall reliability of the equipment.
Using the previous example (20/17/13), this means that at the greater than 4 micron level,
the number of particles measured was at the most 2^20 and above 2^19. Since particle
count data is reported in particles per mL of sample, the raw data must be divided by 100.
While the general rule of thumb is that for every increase in the ISO cleanliness code, the
number of particles has doubled, this certainly is not the case in every situation. Because
the number of allowable particles actually doubles within each code number, it is possiblefor the number of particles to increase by a factor of 4 and only increase a single ISO code.
This becomes a significant problem when you have a target cleanliness level of 19/17/14,
your previous sample was 18/16/13, and your most current sample is 19/17/14. For all
reporting purposes, you have achieved and maintained the target cleanliness level of
19/17/14. This suggests that your component should be in a “normal” status. Given the
information presented previously, it is easy to see how you could have two to four times the
amount of particle ingress and only increase by a single ISO code or have no increase at all.
The ISO cleanliness code should be used as a target. It is a value that is easily tracked for
KPI reporting and a value that most people can easily understand. However, using the ISOcleanliness code for true machine condition support is limited in its effectiveness. The raw
data from particle count testing allows the end user to confirm data from other tests such as
elemental analysis and ferrous index. The ISO cleanliness code does not allow this cross-
confirmation to occur. Reviewing the raw data of the particle counter at all reported levels is
absolutely vital in performing quality data analysis on oil sample data.
• Where does the sample need to be taken on the equipment?
• How are the samples going to be procured?
• How often do samples need to be taken?
• What tests are needed?
Some of these steps can be performed simultaneously, while others must be done in
sequence.
Step 1: The Functions of an Oil Analysis Program
This first step is critical. It provides the direction for nearly all future decisions regarding the
oil analysis program. Can failures be caught early? Are there lube-mixing problems that
need to be prevented or caught before resulting issues occur? Or does the lubricant health
simply need to be monitored to provide accurate lube change intervals? The reasons for
performing lubricant analysis can vary, but overall, the choice can have the most effect on
what can be accomplished with an oil analysis program.
Step 2: Sampled Units
The next problem to tackle is deciding which units to sample. Individual units do not need to
be determined immediately, but for other steps later in the process, it will be necessary to
decide what unit types to sample. Gearboxes only? Super-critical units? Everything? This
step can be one of the most challenging, but when all of the fundamentals are combined, it
is relatively simple due to the limiting factors some steps provide.
The most likely solution is to make a list of everything the user might want to sample and
then prioritize them into groups (definitely want to sample, would like to sample, must be
sampled). Therefore, if the cost is too prohibitive, the units can be pared down to sampling
either less often or not at all.
Step 3: Sampling Location
While this step can be performed in any order, it is useful in helping place limits on the
scope of the sampling project. Sample location is sometimes cut-and-dried regarding where
the sample can be pulled from on the equipment.
The pros and cons of each sampling option must be weighed against many variables
including questions such as "What does the budget allow with the number of units that need
to be sampled?" and "Which sampling method will allow me to monitor what I need to reachthe goal of this project?" In some instances, drop tube sampling is appropriate. Other
instances require a sample point to be installed to obtain accurate and useful data.
Selecting the proper location on equipment may not be as easy as it seems. If the wrong
type of sampling is performed or the sample port is placed in an inactive zone, a unit may
end up failing while the data analysis continues to show positive results.
Safety can also be an issue. Is the unit a high-pressure hydraulic? Be sure to check that if a
sample port is being installed, the pressure rating is within the proper range.
Step 4: Procuring the Sample
If the drop tube sampling method is chosen and only diesel engines are used, this choice is
an easy one. Buy a vacuum gun and get to work. If, however, there are challenges withensuring the proper location has been chosen for taking samples, this can be a significant
problem. There are many reasons why particular units cannot be sampled at any point in
time.
There is always going to be a unit that just doesn't have a feasible solution, but there are
typically solutions for problems if one is willing to dig in and search. Make sure that when
the equipment and sampling method have been selected, the ability to pull the sample
exists as well.
If you encounter a problem while searching for a way to retrieve samples from a piece of
equipment, the equipment vendor may be able to provide a solution. If there is no
equipment vendor available, look up a sampling equipment vendor on the Internet (or just
continue looking through this magazine - there are usually several). If the first vendor
cannot find a solution to the problem, try another one.
Step 5: How Often is a Sample Needed?
Sampling frequency can be dictated by two factors: what the user is trying to find and how
fast it needs to be found. Cost can also be factored in because monthly sampling is not
always an option. However, if cost for having the analysis completed becomes a major
issue, the scope of the sampling project may have to be changed to effectively limit
sampling to a financially manageable situation that doesn't involve randomly removing units
from the sampling plan.
When determining the frequency of sampling, issues such as the likelihood of failure and
equipment history should be addressed while deciding which interval to set up the
equipment.
The more frequently sampling takes place, the more effective one will be at discovering
problems before a failure occurs. Most oil analysis users have heard stories involving a
failure that went from inception to disaster in a matter of days. While this is the exception
rather than the rule, keep in mind that failures can happen quickly, and it is necessary to
limit exposure to that magnitude of failure on units that will cripple operations if they godown.
A functional equipment history may be the difference between a good call and a complete
miss with the analysis. A unit sampled yearly to monitor oil will not provide the analyst with
much equipment history. Quarterly sampling may be the beginning of a stable and
trendable equipment history, and with monthly sampling, there is a 90 percent range of