Clean up your oil and keep it clean! by Dave Whitefield
life can you expect from cleaning
either a 2-part code, or a 3-part code,
Principal Applications Engineer
up your oil?
as specified by the user. The The 2-part
Bently Nevada Corporation e-mail:
[email protected]
• What abou aboutt other other type typess of contamination? • What steps can can you you take take to clean clean up your oil?
ontaminated oil kills machines. Clean oil is one of the most important factors affecting the service life of the
Let’s look at these issues one at a time.
code refers to particle counts in the 5 µm and 15 µm size ranges. A 3-part code of 17/14/12 would indicate 640 to 1,300 particles/mL greater than or equal to 2 µm, 80 to 160 particles/mL greater than or equal to 5 µm, and 20 to 40 particles/mL greater than or equal to
How is oil cleanliness quantified?
15 µm. See Table 1 and Figure 1.
ISO 4406 establishes the relationship
ISO Code
Minimum
Maximum
machinery1. In hydraulic systems, clean
between particle counts and cleanliness
•
•
•
fluid is absolutely essential for success-
in hydraulic fluids (common practice
•
•
•
ful long-term operation. Although Although
has extended the application of the
•
•
•
machines equipped with rolling ele-
standard to lubricants). This interna-
ment bearings are especially sensitive
tional standard uses a code system to
to particulate contamination, machines
quantify contaminant levels by particle
using fluid-film bearings are not im-
size in micrometers (µm). Using ISO
mune to such damage. Many sources
4406, a machine owner/operator can set
cite dramatic improvements in expected
simple limits for excessive contamina-
machine life resulting from even
tion levels, based on quantifiable
modest improvements in lubricant
cleanliness measurements.
a 3-part code to represent the number
10 11 12 13 14 15 16 17 18 19 20 21 22 23
5 10 20 40 80 160 320 640 1300 2500 5000 10000 20000 40000
10 20 40 80 160 320 640 1300 2500 5000 10000 20000 40000 80000
of particles per milliliter (mL) of fluid
•
•
•
greater than 2 µm, 5 µm, and 15 µm,
•
•
•
lubricated components of all
cleanliness. This all sounds reasonable, and
Table 1 illustrates the ISO 4406 cleanliness codes 2. This standard allows
smacks of common sense. Closer
you to quantify current particulate
scrutiny reveals a few questions:
cleanliness levels and set targets for
• How is oil cleanline cleanliness ss quantified? • How clean is “new” oil? • How clean does your oil need to be? • What impro improvement vementss in in machine
cleanup. The current standard provides
respectively . Many labs will report 3
Table 1. ISO 4406 fluid cleanliness cleanliness codes (particles per mL).
For the purposes of this article, and i n keeping with common industry practice, the terms “clean” and “cleanliness” refer to the amount and size of particulate contamination in a lubricating or hydraulic fluid. 1
The ISO standard calls the codes “scale numbers.” You may also f ind them referred to as “range numbers” and represented as R 5/R 15 for 2-part codes and R 2/R 5/R 15 for 3-part codes. 2
The current standard is ISO 4406:1987(E). The ISO is now circulating a draft proposal, ISO/DFIS 4406:1999(E), for contamination levels measured with automatic particle counters calibrated in accordance with ISO 11171. In the proposed standard, the three parts signify the number of particles/mL greater than 4 µm, 6 µm, and 14 µm, respectively respectively (scale or range numbers R 4/R 6/R 14). 3
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Fourth Quarter 1999
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17
/
14
/
How clean does your oil need to be?
12
Each machine
640 to 1300 particles ≥ 2 µm
20 to 40 particles ≥ 15 µm 80 to 160 particles ≥ 5 µm
Figure 1. ISO code example.
class should be
What improvements in machine life can you expect from cleaning up your oil? While it may feel good to know you
evaluated for clean-
have clean oil in your machines, how
liness levels appro-
good can you afford to feel? The
priate to the
answer to this question depends to
application. In gen-
some degree on the specific machine
eral, machines with
application. However, studies per-
tight clearances
formed in many industries all show
and/or anti-friction
dramatic extensions in expected
(rolling element) bearings benefit
machinery life by improving lubricant
Notice each step in the ISO code
greatly from very clean oil. Turbine
cleanliness. In one example, a reduc-
represents either double or half the par-
electro-hydraulic control (EHC) sys-
tion of particles larger than 10 µm from
ticle count relative to an adjacent code.
tems and many aeroderivative gas tur-
1000/mL to 100/mL resulted in a 5-
It is important to note the “/” character
bines are examples of industrial
fold increase in machine life… an
in the written form of the code is
machines that require extremely clean
attractive return on your cleanup invest-
merely a separator, and does not signify
oil for proper performance and long
ment. An additional benefit of cleaner
a ratio of the scale numbers.
life. Filter systems rated to remove par-
oil is a lower noise floor for wear parti-
ticles as small as 3 µm to 7 µm are
cle detection measurements. It’s much
commonly used in such applications.
easier to detect subtle changes in the
Hydraulic systems’ targets should also
amount of wear debris in a clean
be adjusted to cleaner levels for higher
system than in a dirty one.
How clean is “new” oil? Studies of “new” turbine oils, crankcase oils, hydraulic fluids, and bearing oils delivered to customers indicate varying degrees of cleanliness, with ISO codes from a low of 14/11, to as high as 23/20. Drum-delivered products were generally found to be cleaner than bulk-delivered products. Referring to Table 1, you might think twice before putting “new” oil with an ISO 23/20 measurement in your machine.
Improper storage procedures can contribute additional contamination to new oil. Poor handling practices are another source of new oil contamination. (Do
system operating pressures. (See
Society of Automotive Engineers
related article, “Lubrication – A
(SAE) studies have shown engine wear
strategic part of asset management”
reductions of 50% when filtering
on page 6.)
crankcase oil to 30 µm, and 70% when
Table 2 presents some typical base
filtering to 15 µm, as compared with
lubricating oil cleanliness targets for
filtering to 40 µm. By implementing
common machines and machine ele-
some of the measures outlined in this
ments. Like most guidelines, these tar-
article, you will soon be able to docu-
gets are suggested as starting points.
ment your own success stories.
You will probably make adjustments to these levels as you learn how your machines respond to cleaner lubricants.
you know what types of vessels are
What about other types of contamination? As destructive as particulate contamination can be, there are other
used in your plant for transporting and
Machine / element
ISO Target
adding makeup oil? Are they as clean
Roller bearing
16/14/12
as you want your oil to be?) After
Journal bearing
17/15/12
wear. A short list of “non-particulate”
implementing cleanup programs, many
Industrial gearbox
17/15/12
contaminants includes water, coolants,
users find the dirtiest oil in their plant
Mobile gearbox
17/16/13
fuels, and process fluids. The most
is incoming “new” oil. It is clear that
Diesel engine
17/16/13
common of these is water. Water alone
Steam turbine
18/15/12
is a significant factor in lubricant
Paper machine
19/16/13
degradation. When combined with iron
proper filtering of new oil during or before filling is a prudent and highly desirable practice to extend machine
Table 2. Typical base cleanliness targets.
life.
10
ORBIT Fourth Quarter 1999
contaminants that also contribute to oil degradation and premature machine
or copper particles, water becomes even more powerful in attacking
• Measure and trend your progress. (Don’t be afraid to adjust your procedures as needed to meet your targets.) • Document the impact of your investment on availability, maintenance expense, and machine life. With these elements delineated, some of the practical aspects of improving your filtration, storage, and handling procedures can be addressed.
Improving filtration, storage, and handling procedures Many improvements to your filtration, storage, and handling procedures can be made with minimal cost. A little time spent simply reviewing your curFigure 2. Effect of water on rolling element bearing life.
rent storage and handling procedures
lubricant base-stocks and additives. The
bearing lubricant sufficiently to cause
can be revealing (and in some cases,
adverse effects of water in oil include:
journal-to-bearing contact (wiping).
even shocking). Figures 3, 4, and 5
• Lubricant breakdown, through oxi-
The reduction in film thickness also
illustrate a few problems commonly
dation and additive precipitation.
increases the sensitivity of fluid-film
seen in many operations. During the
• Changes in viscosity, affecting the
bearings to particulate contaminants.
ability of a lubricant to maintain
What steps can you take to clean up your oil?
the film thickness necessary to protect the lubricated surfaces.
Let’s say you are now convinced that
• Corrosion.
cleanup is the way to go, but you don’t
• Accelerated fatigue of lubricated
know how to get there. Filtration, stor-
surfaces. Even very small amounts of water can
age, and handling procedures are the key areas to concentrate your energies.
be harmful in machines equipped with
The important elements of a successful
rolling element bearings. Typical life
campaign to clean up your oils are:
reduction of rolling element bearings
• Measure and evaluate current
caused by various concentrations of
cleanliness levels to establish
water in oil is depicted in Figure 2.
baselines for comparison.
Lubricant film thickness in fluid-film journal bearings is substantially larger than that found in rolling element bear-
• Examine and evaluate your current storage and handling practices. • Set cleanliness targets based on
ings, and hydrodynamic pressures are
your goals for longer machine life
typically lower. However, the babbitt in
and/or reduced maintenance and
these bearings, being composed prima-
downtime costs.
rily of lead and tin, is susceptible to oxidation damage from water and oxygen. Water can also reduce the load-carrying capacity of a fluid-film
Figure 3. Poor handling practices – filler neck screen punched out.
• Evaluate, select, and implement the improvements in filtration, storage, and handling procedures required to achieve your goals.
Figure 4. Poor storage practices – loose bung (drum cap). ORBIT
Fourth Quarter 1999
11
through machine components can
scheduled intervals, or in response to
create a self-fulfilling prophecy of
increasing contamination trends in your
machine destruction. Normal full-
oil analysis data. Portable systems can
flow filtering removes some, but
also be used for pre-filtering new oil
not all, wear particles. In fact,
before or during system charging.
many full-flow filtration systems
Cartridge-type f ilters are common on
are only effective in removing
this type of equipment, so you can eas-
particles larger than 40 µm.
ily change to the appropriate filter ele-
Concentrating on the hardest and
ment for the specific cleanliness target
most abrasive particles is an effec-
of each machine or machine class
tive strategy for this category of
being serviced. Since cross-contamina-
contaminants.
tion is a possibility with portable sys-
Once the contamination sources are
Figure 5. Poor handling practices – dirty fill pump.
evaluation phase, it is important to identify contamination sources as well
identified, you can concentrate on the
flushing are essential before use with a
areas most likely to generate your tar-
different lubricant. Maintaining sepa-
get cleanliness levels.
rate systems for each lubricant being filtered is another solution to this
Filtration Offline recirculating (“kidney loop”)
as the levels. Contamination sources
filtration systems can be very effective
may include:
in achieving and maintaining your
potential problem.
Storage and Handling Improvements to storage and handling
cleanliness targets. In some cases, a
procedures can often be implemented
ously mentioned, new oil is often
permanent installation is called for,
at low cost, relative to the benefits.
not as clean as you might think,
with continuous sidestream (“bypass”)
Controlling temperature over a rela-
usually becoming contaminated
filtering. In less critical applications,
tively narrow range is important for
during transportation, storage, and
where sump volumes are usually
proper drum storage. Drums “breathe”
handling.
smaller, the job can often be handled
as the internal pressure increases and
with a cart-mounted portable filtration
decreases with temperature variations.
components can become contami-
system (Figure 6). Portable cart-
Moisture and other contaminants are
nated from handling practices
mounted systems can be used at
forced into the drum when the internal
• Contaminated new oil. As previ-
• Built-in contamination. Machine
pressure decreases. In most climates,
encountered during overhauls or
this problem must be addressed by stor-
rebuilding processes. It is impor-
ing drums in enclosed, temperature-
tant to review shop procedures
controlled storage facilities. Shielding
relating to cleanliness of internal
storage containers from dirt and mois-
wetted parts, hoses, and lubricant
ture are other obvious measures that
piping.
will keep your new oil in good condi-
• Ingested contamination.
tion. Be as careful with pumps and
Unfiltered sump vents and faulty
transfer containers as with your storage
seals are common problems which
containers. This will minimize the
can result in contaminants (includ-
chances of cross-contaminating with
ing water as well as particulates)
other lubricants and introducing con-
entering the lube system from the
taminants into machines when topping
outside environment. Minor modi-
or filling.
fications to vent systems can reap rewards in this area.
Water removal
• Internally-generated contamination. Recirculating wear particles 12
tems, filter changes and adequate
ORBIT Fourth Quarter 1999
Since the sources for water contamiFigure 6. Portable filter cart.
nation are so numerous and ubiquitous,
eliminating all sources of moisture can be very difficult. Removing water from
• Filter/Dryers
cleanup has proven to be one of the
Cartridge-type filters that use
simpler and more cost-effective meth-
oil can also be a challenging task, but
super-absorbent materials to
ods of achieving measurable improve-
there are several methods available.
soak up water.
ment. Don’t wait for contaminants to
Dissolved water isn’t removed.
destroy your machines. Clean up your
Each method has advantages and disadvantages, so each must be carefully evaluated for the particular application. Some of the common methods for removing water from oil, along with
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• Vacuum Treating (Vacuum Dehydrating) L
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since it is a chemical separa-
water to separate it from the oil,
tion.
and water escapes from the L
Inexpensive.
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Least effective of known
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being a highly-effective lubri-
Properly-designed reservoir is Only free water is removed.
cant purification system. • Gas Sparging/Air Stripping L
• Centrifuging (Centrifugal Separation) L
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Entrained gases aren’t removed.
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Emulsified water content tends
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Additives are not removed.
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Nitrogen or air can be used.
Dirt and other solids are removed.
cleanliness levels of the lubricants you
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Additives can be removed by
purchase. You may pay a little more up
this method.
front, but the savings in machine avail-
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A coalescing cartridge filter is used to separate the water from the oil.
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Additives can be removed by this method.
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3. A Guide to Standards for Contamination Specifications in Liquids, Pacific Scientific Instruments, HIAC Royco Division. 4. ISO/FDIS 4406:1999(E), International Standards Organization. 5. Industrial Oils, Chevron USA, Incorporated. 6. The Handbook of Hydraulic Filtration, Parker Hannifin Corporation, Parker Filtration Division. 7. Machine Design, “How Dirt and Water [Affect] Bearing Life,” Timken Bearing Company.
An additional cleanup step, which is
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Only free water is removed.
2. Fitch, J. C., Oil Analysis Course Manual , Noria Corporation, Tulsa, Oklahoma.
Purchasing clean oil often overlooked, is to specify the
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1. Toms, Larry A., Machinery Oil Analysis, 2nd Edition, Coastal Skills Training, Virginia Beach, Virginia.
Dissolved, emulsified, and free
to increase.
• Coalescing Filters/Screens
References
water are removed.
ppm by weight, above the saturation point.
The chemical separation principle of air stripping is used.
Only the free water form of water is removed to about 20
When combined with effective filtration media, capable of
methods. required.
Dissolved, emulsified, and free water can be removed.
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L
Additives usually aren’t removed from the lubricant,
Natural – gravity acts on the
fluid via natural evaporation.
The wet lubricant is heated in a vacuum to separate the water.
their tradeoffs, include: • Settling/Evaporation
oil and keep it clean!
ability, filtration costs, and machine life extension often more than offset the additional cost. If you choose this route, be sure to test the incoming oil to verify you get what you paid for.
Conclusion It’s best not to take administration of
Only effective for narrow
your oils lightly. Attention to detail is
ranges of viscosity and specific
paramount in achieving cleanliness lev-
gravity.
els that produce large improvements in
Some manufacturers claim “No
machine life and availability. When it
removal of additives.”
comes to machine life, lubricant
ORBIT
Fourth Quarter 1999
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