Water is often overlooked as a primary cause of component failure.
Yet, water contamination can reduce bearing life by as much
as 90%.
Not only does water have a direct harmful effect
on machine components, but it also plays a direct role in
the ageing rate of lubricating oils. The presence of water
in lubricating oil can cause the progress of oxidation to
increase tenfold, resulting in premature ageing of the oil
(particularly in the presence of catalytic metals such as
copper, lead and tin).
There are a number of onboard test devices that can help
engineers identify and determine the levels of water contamination
from an oil sample. Guidelines of minimum/maximum limits and
suggested action plans are useful references to help engineers
decide on the appropriate course of action.
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Should
you replenish oil additives?
Over a period of time oil additives are depleted, performing
the function for which they were formulated. They are degraded
by hydrolysis, mechanical shearing, condensation settling, water
washing, particle scrubbing, etc.
The rate of depletion or degradation depends upon the application
and the environment. In particular, heat, pressure, shear
rate, fuel sulphur, soot, dirt, water, aeration and the presence
of catalytic metals (copper, iron, etc.) affect the rate of
depletion.
Everytime you top-up a system, you are in effect replenishing
additives. Likewise, one can perform a partial drain and replacement
(often referred to as bleed and feed). A bleed and feed can
work if the base oil is not degraded. If the base oil has
been degraded, adding new oil is analogous to sending a healthy
person into a room full of sick people with the hope that
his or her good health will be contagious - it doesn't work
that way. The additives in the new oil might be compromised
within the first hours of use, leaving you right back where
you started.
Should you perhaps reclaim or recycle the oil?
It is important to understand the difference between oil
recycling and oil reclamation, so let's start with an explanation
of each:
(a) Oil Recycling : any treatment that completely restores
the original lubricating properties of the oil (re-refining).
In this context, recycled oil can be put back in service as
a formulation differing from the original, and/or possibly
in an application with less stringent lubrication requirements.
For example, heavily oxidised oil, admixed formulations and
some chemically contaminated oils cannot economically be reclaimed.
However, they can be recycled and rendered useful again for
the same application by re-refining them, stripping out all
additives and re-additizing them. Re-refining is not a simple
process nor is it as economical as reclamation.
Common used oil recycling methods:
Re-refining of used oil, to use as a base stock for lubricating
oil. This recycling option applies physical and chemical
treatments to the used oil to remove impurities until the
re-refined oil is of as high a quality as the virgin oil
product. In addition, re-refining takes from 50 to 85% less
energy than refining virgin oil into lubricating oil. One
disadvantage of re-refining is that it is more complicated
and expensive than other recycling options. However, re-refining
used oil into lubricating oil is easier and less expensive
than re-refining crude oil into lubricating oil, and the
costs associated with re-refining used oil usually can be
recaptured when the lubricating oil is sold. A second disadvantage
is that only a few re-refining facilities are currently
in operation worldwide.
Slipstreaming used oil, to use as a base stock for other
petroleum products. This method is done by introducing small
amounts (approximately 1% of the feedstock material) of
used oil into the virgin oil refining process. The refining
process then removes all contaminants in the used oil that
will affect the quality of the resulting petroleum product.
The major advantage of slipstreaming is that the lubrication
value of the used oil can be utilized without complicated
processing methods. In addition, slipstreaming poses no
greater environmental risk than refining virgin oil. Lack
of availability is the main disadvantage, however, it is
expected that slipstreaming and re-refining may become more
available in the future.
Processing used oil, to burn for heat. This method involves
treating used oil so that it will make a better fuel. Processing
used oil is a widespread industry (there are almost 200
processors in the USA alone). Also, processing improves
the burning quality of used oil, allowing it to be burned
by a greater number of burning facilities.
Direct burning of used oil for heat. This method burns
used oil without processing it first to remove contaminants.
The major advantage is that it allows the heat value of
used oil to be utilized without the expense of processing
the used oil before burning. Facilities that generate large
amounts of used oil (eg power generation) find this method
quite attractive.
(b) Oil Reclamation : the act of salvaging, recovering or
reclaiming of oil involving the removal of contaminants and
degradation products. For example, dirty, wet oil with a low
additive content may be a candidate for reclamation because
the dirt and water can be removed. Through the guidance of
an expert in formulations (or from the oil supplier), the
additive package may be refortified. The oil can then be placed
back into the same service for which it was originally formulated,
in a condition suitable for continued service. In most cases,
performance analysis on reclaimed oils is recommended to confirm
“like new” or “fit for service” condition.
It is usually futile to attempt to recondition lubricants
that are showing signs of oxidation. This is evidenced by
rising Acid Number, increased Viscosity, and darkened oil
colour. When in doubt, confirm by laboratory analysis whether
a used lubricant or hydraulic fluid is a candidate for reclamation.
Casual addition of additives into a formulated oil, without
the guidance of detailed oil sample analysis and the advice
of an expert, can be dangerous and should be avoided. Lubricant
suppliers discourage such practices. This is more so when
the equipment is still under warrantee, or it has a very high
cost of replacement.
36%
of all bearings fail prematurely due to incorrect lubrication
Choosing the right bearing grease for the right application
is critical to bearing performance. Conditions such as load,
speed, temperature and environment determine the type of grease
needed for the application. Injecting the correct quantity of
grease is also of paramount importance, since over-greasing
can contribute to machine downtime and early failure.
Fitting
an automatic grease lubricator on pumps, fans, cranes etc,
would ensure long term lubrication at the point of application.
Ideal for providing safe, clean, cost effective lubrication
in difficult to reach or restricted areas. Users are able
to control the amount of grease used in each application,
by setting the dispense rate on the timer of the lubricator.
Grease levels can be checked through the transparent container.
For more information on automatic lubricators, email us at
Hints
and Tips
Filters are commonly classified according to absolute or nominal
ratings. A filter that is classified absolute has an efficiency
of 98 % or better at the specified micron size, and a filter
that is classified nominal has an efficiency of between 50 %
and 95 % at the specified micron size.
Hydraulic
oil darkening
"After taking a sample from a hydraulic system
you notice the hydraulic fluid has become darker. Concerned,
you rush a sample to the oil supplier for analysis. The results
of the oil analysis appear normal: Acid number, Viscosity and
FTIR-Ox (oxidation) have all remained stable. A quick inspection
of the hydraulic system reveals that the hydraulic valves have
turned goldish in colour. What would you do?"
The goldish colour on the valves is varnish, which you would
also find on all surfaces of the tank, piping, valves and
the sight glasses. You are also likely to notice a change
in the oil's smell. The problem is due to thermal stressing
of the oil, as opposed to straight oxidation. Most likely,
a valve has failed on a subsystem, forcing oil through a small
orifice, causing it to overheat. Because it is a small localized
hot spot in a large tank and oil cooler, the high temperature
would never be detected as a rise in bulk oil temperature.
The first indication of a problem would be the change in the
oil’s colour.
Initially, you should confirm this with further oil analysis
and if proven, drain, flush and clean the system with a solvent
or an oil that is compatible with the current operating oil.
Want to know more? The fact that
the acid number, viscosity or FT-IR-Ox have not changed indicate
that oxidation is not taking place in the hydraulic oil. However,
the golden residue on the valves is a clear sign that varnish
is precipitating out of the fluid. Since varnish is composed
of fluid degradation by-products, then thermal degradation
is likely to be the cause of the fluid deterioration (which
occurs in the absence of oxygen). Left untouched, this varnish
will impact the valve's capability to function properly.
The cause of thermal degradation is heat. Two of the most
common sources of extreme temperatures in a hydraulic system
are (a) a hot spot caused from an external heat source in
close proximity to the lube system, or (b) the implosion of
entrained bubbles as the bubbles flow from the reservoir into
higher pressure zones like the pumps or valves.
Three steps to address this problem:
(1) Confirm that thermal degradation is indeed the source
of the problem. Ask the laboratory to provide the FT-IR curve,
and instead of looking at the wavenumber region where oxidation
levels are measured (1714 cm-1), look for a peak in the nitration
region (1630 cm-1), to confirm it is indeed thermal degradation.
(2) Perform a root cause analysis to investigate the source
of the heat in the system and determine if it is a system
design flaw or if there is a solution that could be engineered
to remove this heat source. If the problem appears to be entrained
air, there are technologies available to remove bubbles from
the hydraulic fluid to solve this problem.
(3) If thermal degradation is a result of system design,
utilize a separation technology to remove the thermal degradation
byproducts from the fluid, providing a permanent band-aid
to the varnish formation until system redesign can be accomplished.
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