SYSTEMS, STRATEGIES & RESEARCH FOR LUBRICATION PROFESSIONAlS
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establish condemning limits
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DO YOU FEEL LUCKY?
It' mor than a classic
line from a Clint Eastwood movie, it's what fleet
managers-those responsible for determining
when fluids need to be changed-regularly ask
themselves. Why? Because uniform condemn
ing limits ar hard to come by.
Uniform oil analysis test procedures, on the other hand, are established and reviewed by such agencies as the Interna
tional Organization for Standardization (ISO), the American Society of Testing Materials (ASTM) and the Society of Auto motive Engineers (SAE).
Having uniform oil analysis test procedures without uni form condemning limits-is like having an accurate blood cholesterol test but no kpowledge of how high is too high. You could spend years perseverating over every pat of butter or you could throw caution to the wind and end up suc cumbing to a Single scoop of ice cream.
Establishing uniform condemning limits, though, is not really possible for a number of reasons i~cluding the vari ability of engine-use conditions. This leaves one or the other user in the position of having to make an educated guess as to when to change fluids. If they change flUids too late, they risk engine damage; too early and they waste money.
"Any report showing a severe condition will indicate that the problem needs to be addressed immediately and there is ],illic margin of safety until the situation is addressed," says Ted Savage, business manager-central for ALS Tribology in Kansas City, Kan. "Some action or investigation at some level should be instigated in a timely manner. The action may be as simple as asking yourseU, 'Can I live with this amount of fuel dilution if it does not get worse?' As the rate of change of wear, contaminants and oil degradation increases, the safety margin decreases. The margin of safety may be very limited when rates of change for excessive wear and contaminants and oil degradation increase during an abnormal condition." The scope of this article is limited to oils for internal com bustion engines large enough to warrant used oil analysis. TESTS AND
CONDEMNING LIMITS
All oil analysis programs are deSigned to be performed as a trend anaiysis, requiring a series of regularly scheduled sam ples. "We derive condemning limits from several sources," says Savage. "ALS will work with lubricant manufacturers for condemning limits related to contaminants and lubricant properties as well as OEMs for condemning limits related to equipment deSign wear, contaminants and lubricant proper ties."
In addition to the condition of the oil itself, other consid erations include:
• Thc hours andJor mileage on the oil • The OEM-specified oil drain interval • The engine's total run-time
• The expected lifespan of the machine.
Tracy Wolf, gas engine customer service for Caterpillar, Inc. in Lafayette, Ind., explains, "As the engine ages, items such as piston rings, liners, valve guidcs and valve stem wear. This leads to more rapid contamination of the oil and, hence, can lead to a shorter drain interval. Deposit build-up and
internal component wear is espeCially critical in biogas fuel applications. "
Ideally, the oil analysiS records of each piece of equipment includes baseline data and results of samples taken at regular intervals. Experts in most fields say that establishing a trend requires at least three samples.
"The goal of using trending analysis is to detect problems before they become major issues and plan accordingly," says Savage. "The consequences of exceeding puhlished limits are related to assessing the overall situation. Does the problem represent a potential catastrophic situation if it is not ad dressed immediately? Does the severity of the situation allow planned shutdown and repairs that will be most economical and least disruptive to business? Equipment reliability will not be compromised if addressed in a timely fashion. Some times a single test parameter needs to be addressed immedi ately if it represents a root cause that will lead to greater problems in the near future.
"Sometimes," Savage adds, "a Single test parameter is not going to justify immediate action if all other test results ap pear normal. Awareness of the condition is all that may be requ,ired at this time. Usually looking at multiple parameters in a test report gives the best assessment of equipment condi tion. There are times when no Single test parameter has reached a condemning limit, but the overall trend for multi ple parameters is showing an increased rate of detrimental change, indicating it would be prudent to take action before problems accelerate to a serious condition."
But these tests are less significant without sensible con demning limits in place-set by OEMs, independent oil anal ysis labs and, in largc operations, end-users.
COMMON OIL PROPERTY EVALUATION TESTS
Oil analysis programs address such ar eas as abnormal wear rates for internal engine parts, the state of oil additive packages, the level of contamination and the physical condition of the oil.
Disagreements e~ist regarding
which of the multiple oil condition pa rameters are most critical to monitor and which thresholds determine the oil change interval. One of the most exhaustive data-gathering exercises on the variations among condemning limits set by different OEMs was con ducted by the U.S. Army in 1999. Re ferred to as the Marbach-Frame Re port, its purpose was to identify the best methods of field testing used oil. But the report was so thorough that it yielded a wealth of data relevant to condemning limits. This report is still cited today.t
The information revealed that the recommended oil change interval var ied significantly among OEMs. 2 Oil
viscosity, however, was agreed upon as the most critical parameter related to both oil degradation and engine con dition and Total Base Number (base number) was considered to be a sig nificant parameter for determining the extent of oil degradation.)
Maintenance personnel identify set properties to evaluate the condition of the oil and equipment. These proper ties include the following:
Viscosity. This measures the oil's re sistance to flow. The ideal viscosity is extremely important to performance and equipment life. In addition, the Viscosity Index (VI) can indicate many abnormalities.
Water Content. Water gets into the crankcase through gasket leaks, water pump seals and condensation that oc curs during cool down. Moisture can promote oxidation and corrosion.
Lubrication Engineers, Inc., of Fort Worth, Texas, uses the following con
demning limits as a very general guide for oil changes:
4• Viscosity: a change of 10% to 12% (either up or down).
• Acid Number: 6.5 or above or an increase of 1.0 to 2.0.
• Base Number: Areading below 2.0 indicates additive protection level
is low.
• Pentane: A0.5% insolubles reading (total carbonaceous solids/
metals).
• Toluene: A0.25% insolubles reading.
• Fuel Dilution: A3.0% reading.
• Water: A1% reading for water calls for attention; 2% calls for
change.
Lubrication Engineers has the following caveats: Aneutralization number
alone is of no value. Interpretation can be used only with the other test
results and the many variables as outlined in the operating and environmen
tal data submitted with the sample; a trace of metal is a concern (a measur
able amount requires prompt investigation). Even a trace of glycol requires
prompt investigation (a measurable amount means immediate inspection of
the engine). In spectroanalysis, sodium, potassium or boron levels higher
than normal would indicate glycol (a coolant leak).
I Marchback, H.W. and Frame, E.A. "Investigation of Portable Oil Analysis Requirements for Army Application." J.999. Full text available at:
http://www.dtlc.mil!cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA397159.
, On-Board Monitoring Of Engine Oil by Ryan James Clark, M.s.£. Available at: http://www,dtic. mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA538688
1 Ibid
Coolant/Glycol. Glycol breaks down at high engine temperatures, which leads to water evaporation. The glycol then forms sludge which reduces filterability. Large quantities corrode bearings and block oil flow.
Fuel Dilution. Fuel dilution is caused by in complete combustion brought about by ex tended periods of idling>or by using a heavy fuel. It may also be caused by a malfunctioning or improperly sized fuel injector or from worn liners or piston rings that end up dumping too much fuel iJ:lto the system.
Acid Number. This measures the total amount of acidic products in the oil, indicating the level of the oil's oxidation.
Base Number. This measures alkalinity. As oil ages, alkaline additives neutralize the com bustion acids, and alkalinity decreases. Oper ating with low base number oil can lead to wear and deposit formation. The alkalinlty can only be restored by adding or changing the oil.
Insolubles. In addition to oil-insoluble mate rial, this also measures some oil-soluble resin ous material that originates from oil ancIJor ad d itive degradation.
Soot. Soot is usually caused by delayed in jection timing and is an indication of poor air to-fuel ratio. Along with increased viscosity, excessive soot causes abnormal valve and in jection-train wear. It can increase exhaust emissions and clog filters.
Elemental Analysis. This tracks the additive and wear elements, wear metals, and contami nants in oil. The concentration of wear metals can indicate abnormal wear and also indicate an incorrect oil is being used. In addition to monitoring equipment condition, it can detect coolant leakage.
Particle Count. Particle count is recom mended for use in conjunction with wear met al analysis because it detects wear and deterio ration of synthetic friction materials on discs. It also detects the larger worn particles.
According to Bill Briggs, director-field ser vice of GE's Waukesha gas engines division in Waukesha, Wis. (and in line with Savage's comments) within the parameters that are set for different types of oil, condemnation limits are generally well-established and conservative to protect the gas engine. However, condemna tion limits of the individual constituents of the oil are reached at different times in different gas engines, depending on the combustion sys tem of the engine, the characteristics of the
Following are the engine condemning and industrial condemning limits
that Petroleum Technologies Group of Grand Rapids, Mich., has set:s
ENGINE CONDEMNING LIMITS
• Wear Metals: These limits are established by trend over a number
of samples.
• Solids: The limit for solids (an accumulation of all products in the
sample such as metals, dirt, soot and etc.) is 5% by volume.
• Soot: The limit for soot (combustion products) is 3% by volume.
• Viscosity: The limit for viscosity is an increase or decrease of one
grade.
• Fuel Dilution: The limit for excessive fuel in the oil is 2%. Equip
ment that frequently idles may reach 3%.
• Antifreeze: The limit for antifreeze is any trace amount. There
should never be any amount of antifreeze present in the oil.
• Water: The limit for water is 0.3%.
• Oxidation: The condemning limit for oxidation is 75% of allowable.
• Nitration: This reading indicates nitrate acids building up in the
system. The condemning limit for nitration is 75% of allowable.
• Sulfation: This reading indicates sulfur acids building up in the
system. The condemning limit for sulfation is 75% of allowable.
INDUSTRIAL CONDEMNING LIMITS
• Wear Metals: Limits are established by trend over a number of
samples.
• Solids: The limit for solids is 1% by volume. This is an accumulation
of all products in the sample such as metals, dirt, etc.
• Antifreeze: The limit for antifreeze is any trace amount. There
should never be any amount of antifreeze present in the oil with
the exception of water glycol oils.
• Water: The limit for water is 0.3%. The exception is turbines at
0.1%.
• Oxidation: The condemning limit for oxidation is 75% of allowable.
• Nitration: The condemning limit for nitration is 75% of allowable.
This reading indicates nitrate acids building up in the system.
• Sulfation: The condemning limit for sulfation is 75% of allowable.
This reading indicates sulfur acids building up in the system.
• Particle Count: The limit is determined by the manufacturer of the
system and usually will be determined by the type of pump, valves
and pressures in the system.
• Additive Metals: These metals include zinc, calcium, phosphorus,
etc. The condemning limits are determined by knowing the new
oil's starting point and using a 25% drop.
fuel and the environment in which the gas en- 5 From: http://www.oil-lab.eom/downloads/Petroleum_Tee hnologies.pdf.
I
gine is operating.
In practice, however, rarely, if ever, are all of the constitu ents of used oil tested to determine their condition. Once oil passes published condemnation limits, it is difficult to deter mine ,the point at which damage to the engine will occur because of the degradation of anyone or more of the con stituents in the oil. Therefore, once any oil constituent reach es its condemnation Iiroit, it's time for the oil to be changed.
Most experts agree that the NO.1 indicator of a fluid's quality is viscosity. This goes decades back when mainte nance workers used to "eyeball" the condition of the fluid. Another early method for testing viscosity was to place a drop of oil on a paper towel to see how far it spread. Even though today's viscosity methods are far more sophisticated, expert eyeballs are still a good indicator.
An increase in viscosity is due partly to evaporation of lighter base oil fractions and also the loss of volatile oil deg radation products, high-temperature oxidation, water, cool ant contamination and soot accumulation. Excessive oil vis cosity can hamper oil flow to critical engine components, especially during low temperature startups. Continued use of overly viscous engine oil can cause severe problems, lead ing to seizure and failure in the extreme.
A decrease in oil viscosity usually indicates fuel dilution but in multigrade oil can be caused by shearing of the VI im prover. Using an oil with a viscosity that is too thin can result in high oil consumption, stress on critical parts and compo nent failure. (Editor's Note: For more on VI improvers, see the
API CJ-4 OILS
The American Petroleum Institute's API CJ-4 oils have
additive systems that are designed to improve the
protection of both the engine power system and ad
vanced emissions control system components such as
diesel particulate filters (OPFs).
In addition to helping to maintain the life of the
emission control system for regulatory compliance,
compared with previous API performance categories, API
CJ-4 oils are formulated for improved wear protection,
deposit and oil consumption control, soot-related
viscosity control, prevention of viscosity loss from shear
ing, used
oil low-temperature pumpability and protection
from thermal and oxidative breakdown. They contain less
ash and lower amounts of ZOOP (zinc dialkyldithiophos
phate), an antiwear additive.
There is disagreement as to whether API's CJ-4 oils
increase drain intervals. Specific oil drain recommenda
tions vary widely, depending on engine type, duty cycle,
fuel type and other factors. API recommends that users
seek guidance from engine or vehicle manufacturers
regarding specific service recommendations.
September 2011 TLT issue, available digitally at www.stle.orC].)
OEMs, independent labs and large fleet operators use these tests to define condemning limits.
"Generally ALS does not override engine manufacturer limits, which would be the standard we go by," says Savage. "ALS house limits are only incorporated when there is no available information from the OEM. We work directly with some equipment manufacturers to establish new or updated oil limits for their product."
"It's not unusual for ALS to work in conjunction with equipment manufacturers and partner to develop OEM lim its," Savage adds. "These normally consist of using data col lected for the OEM through one of our testing programs and then applying the data to equipment manufacturing designs and applications. This is useful when new equipment de signs are created and put on the market."
SETTING LIMITS USING STATISTICS
Independent analysis labs and OEMs use several approaches to determine condemning limits. The most common, and most readily adaptable to customize user limits for some pa rameters (like wear metals), is to use a Simple statistical model to analyze the data range of similar components with similar drain intervals. This model assumes that elemental concentrations from similar equipment fall into a normal distribution pattern. Calculating the average is as basic as summing all the values and dividing by the number of val ues. However, it's also important to know the range of ac ceptable values and determine the standard deviation.
Once the normal distribution value range and standard deviation are established, any value falling outside the stan dard deviation or a multiple of the standard deviation is cause for investigation.
The value of this approach to setting wear metal limits is that it fairly accurately represents the expected wear metals concentrations in used oil samples, as long as the data set is large enough and appropriate. Today, most oil analysis soft ware and even standard spreadsheet software can easily cal culate the average and standard deviation for a selected sam ple population.
A critical key to establishing a condemning limit based on statistics is accurately defining the data set. That means iden tifying samples by factors that include:
• Equipment type • Component type • Manufacturer • Function • Oil type • Functional environment.
As long as there is sufficient data available, the statistical approach for setting condemning limits applies to fleet equipment as well as stationary plant equipment.
"At GE, oil condemnation limits are reached at different times in different gas engines, depending on the combustion system of the gas engine, the characteristics of the fuel and the environment in which the gas engine is operating," Briggs explains. "GE's Waukesha gas engines division bases oil cond~mnationlimits on a combination of long experience with the operation of the engines and working with large oil manufacturers who conQuct extensive laboratory tests."
Often engine oil manufacturers will work with their cus tomers to set up a used oil test program. The customers will send samples of their used oils to the manufacturer who will run tests on the oil to detennine its condition. Theoretically, this should allow [leet managers to extend the oil drain inter val out as far as they can. But one of the big questions is whether OEMs are setting limits too high just to be on the safe side.
Savage says, "If no speCific limits are provided by lubri cant manufacturers or equipment manufacturers, ALS calcu lates limits using its database to statistically derive limits based on data population related to specific equipment de sign and lubricant application. It is not unusual to also de velop limits by working with specific clients or end-users to meet their needs. We will work with clients to set optimal limits, which will ensure optimal equipment performance for their specific need or application.
THE MARBACH-FRAME STUDY
This groundbreaking work was undertaken by H.W Mar bach,
Jr.,
and E.A. Frame at the U.s. Army TARDEC (Tank Automotive Research, Development and Engineering Cen ter) Fuels and Lubricants Research Facility (SwRI) South west Research Institute in San Antonio, Texas.Marbach and Frame began by compiling a list of the ma jor component manufacturers of engines, transmissions, hy draulic systems, generators, and manual transmissions/final drives typical of U.S. Army ground equipment.
Next, they contacted these manufacturers to obtain their oil analysis recommendations, and change criteria for oil degradation and equipment condition (essentially condemn ing limits). Using this information, along with TFLRF (The Fuels and Lubricants Research Facility) personnel experi ence, they compiled a list of key parameters of used oil prop erties. They identified properties required for oil monitoring and/or component monitOring. Then they developed critical oil analysis requirements for compression ignition engines, turbine engines, power shift transmissions and hydraulic systems.
Once they received the manufacturers' oil-change crite ria/guidelines, Marbach and Frame compiled tables for oil change properties, along with the properties' ranges for en gines, transmissions, hydraulic systems, drive axles and manual transmissions.
The authors discovered that three of the major engine manufacturers had slightly different points of view about the importance of certain parameters in their engine recommen
dations. One author recommended wear metal analysis for detecting oil contamination. Another considered the follow ing primary oil characteristics to be warning Signals: viscos ity, [lash point and elements silicon, boron, sodium and po tassium. A third manufacturer recommended using primarily viscosity and base number to establish engine oil condition.
Once oil passes pUblished condemnation
limits, it is difficult to determine the
point at which damage to the engine
will occur.
The two researchers determined that most hydraulic sys tem manufacturers required viscosity, water content and par ticle count, while the neutralization number and flash point are generally recommended for fire-resistant hydraulic flUid. All except two drive-axle and manual transmission OEMs recommended hard time intervals for lubricant changes.
Basically, Marbach and Frame found that there was sig nificant variation in oil drain recommendations among OEMs.
Marbach and Frame then identified critical lubricant analyses properties based on equipment/component manu facturer oil analysis requirements. Next they categorized critical oil properties and contaminants into three levels based on cost and risk. Since the ultimate goal of the study was to create a portable (in the field) method for testing oil, the cost factor was the estimated cost of the required analysis equipment. The risk factor was defined as a subjective esti mate of the risk of not detecting a problem.
Level 1. This included the minimum used oil properties
(viscosity, water/glycol, acid number, wear metals) that must be determined to provide reasonable equipment protection. This least costly set of properties would involve the highest level of risk that a problem would be missed.
Level 2. This intermediate level included all Levell prop
erty analyses plus soot content, insolubles, base number and wear particle analysis.
Level 3. This ultimate analysis included all Levelland
Level 2 analyses plus Fourier-Transform Infrared (FTIR) and spectrographic techniques. Level 3 has the highest estimated cost and lowest estimated risk. Level 3 provides the most detailed oil analysis, but test equipment costs rise commen surately.
While most oil analysis end-users don't own their own analysis equipment, the cost of the equipment affects the cost of the test, meaning equipment cost in this study can be roughly proportional to test cost. The three test levels that Marbach and Frame developed are a good starting point for identifying test depth and frequency for various types of equipment.
DETERMINING DRAIN ,INTERVALS
The Marbach-Frame Study is extremely valuable for fieet managers and maintenance personnel in every industry be cause of the nature of the equipment under study. Because they were considering military equipment, they were fully aware that not only was the equipment at risk, but, far more important, lives. A diesel engine breaking down on the high way is one thing, a tank breaking down in the middle of a firefight is quite another.
That Marbach and Frame were asked to look for ways to not only speed and optimize reliability of oil analysis but also reduce the cost of oil analysis for critical battleground equip ment is a telling indication of how costly the problem of drain interval ambiguity is. In fact, their goal was to reduce the number of used oil samples sent to remote testing facili ties by approximately 80% through the use of onsite equip ment andJor reducing the number of samples.
There is a movement in the trucking industry to extend drain oil intervals as far as possible-partly through adop tion of API CJ-4 specifications. As mentioned above, the drain interval depends on a number of factors that qualify the condition of the oil but don't necessarily show up in oil analysis results. One of those factors is the operating envi ronment. For example, a diesel truck that is constantly haul ing heavy loads up steep dusty roads is going to have a drain interval quite different from the same make and model that goes on long hauls over highways.
Wolf says that nearly all customers are very concerned about extending oil drain intervals for the following three reasons:
• Cost of equipment downtime to change oil and filters • Cost of the oil and filters
• Cost of disposing of the used oil and filters.
One suggestion for determining (and possibly extending) drain intervals using a statistical method is to remove as many variables as possible. For example, remove the envi ronmental variable by dedicating specific equipment to spe cific operations.
Susanne Chvatal, engine engineering and oil management of GE's gas engines division, says, "A specific oil quality re sults in a typical oil drain interval. If a customer needs ex tended drain intervals, we can recommend products of a quality that provide a longer drain interval. Complaints about insufficient oil quality usually do not occur if customers fol low our oil management guidelines, which include using an approved oil, analyzing oil samples in a defined interval and program and maintaining the oil below condemning limits." CREATING A BALANCE
When it comes to setting condemning limits and determin ing drain intervals, there are several interested parties:
• The OEM
• The independent test lab
• The fluid manufacturer • The EPA and environmentalists • The end-user.
Their interests aren't all mutually exclusive. For example, it's not in anyone's best interest for equipment to fail or to pollute the environment with waste oil. Ultimately, it's up to the end-user to determine which condemning limits make the most sense and whether it's feasible or advisable to create a set of independent, organization-specific limits. Only the end-user can determine the organization's margin of safety, its take on the risk versus cost continuum.
According to GE, some of the potential consequences of exceeding established condemning limits include:
1. When oil deteriorates, it can build up behind the pis ton rings. That causes the ring to push out, which wears out the ring and the liner against which it moves. As a result, there is no place for the oil to sit on the liner, which, in turn, leads to scoring of the liner and piston.
2. Deteriorated oil can leave varnish-like deposits on pis tons that damage the rings and the liners.
3. These varnish-like deposits can form on valve stems, which can cause the valves to stick. A sticking valve can be hit by the piston and break, which could cause a major failure of the engine.
4. When the acid content of the engine oil exceeds con demnation limits, it can cause acid attack or bearing corrosion, which can lead to bearing failure.
5. Wear metal particles or environmental debris in the oil can damage bearings in both the engine and the turbocharger.
"The end result in exceeding a published limit can affect equipment reliability, work interruption, equipment life and resell value, repair costs, even safety and increase the eco nomic impact of maintenance and repair costs," says Savage. "A test result outside of an acceptable range should be inves tigated and not ignored so the reason for the out-of-limit test result is understood. It may be the published limit is too stringent. There may be a unique situation that forces a test result outside of the normal range due to the environment or local application."
Concludes Savage: "With some parameters for test oil and equipment, the question to ask is, 'Can I live with this situa tion and for how long?'''
ii!i
Jean Van Rensselar heads her own communications firm. Smart PR Communications. in Naperville. III. You can reach her at [email protected].