TECHNOLOGY
FEATURE
OIL CHANGE
Oil degradation
O
By Jonathan Njine
Jonathan Njine is the
MD of lubesol limited,.
Lubesol are appointed
distributors of various
specialty lubricants.
il or lubricant degradation is the main reason why lubricants require
being changed and is responsible for many kinds of equipment
failures. A lubricant in service is subjected to a wide range of conditions
which can cause degradation of its base oil and additive system. Such
conditions or factors include heat, entrained air, incompatible gases,
moisture, internal or external contamination, process constituents,
radiation and inadvertent mixing of a different fluid. If an oil is used in a total loss
application, where the oil is disposed after one cycle of lubrication, such as a drip-feed,
picking up of moisture and dirt is not a factor, as the oil is used once then discarded.
Left untreated, industrial oils will degrade over time, through exposure to external
influences such as water, particles and dirt, through the breakdown of oil additives,
and through the process of oxidation.
Contamination by particles
Most oils are used in enclosed systems or
reservoirs, however, where they re-circulate
through the operating system. As the oil
re-circulates, it lubricates, cools and flushes
away debris from normal wear particles and
cleans the equipment parts. This wear debris,
depending on the size of the particles, may
settle in the oil reservoir, be removed by the
filters, or simply be re-circulated, if it is too
small to be removed. Sometimes, the wear
debris can remain in the oil not settling as
expected.
These particles not settled but still
suspended in the oil, cause damage through
abrasive wear each time they circulate through
the lubrication system.
Research conducted over the past few
years demonstrates that particles as small as 5
microns, when present in large quantities, will
cause severe pump and valve wear by acting as
a lapping compound.
Foreign substances can greatly influence the
type and rate of lubricant degradation. Metals
such as copper and iron are catalysts to the
degradation process like oxidation. Water and
air can provide a large source of oxygen to react
with the oil. Large amounts of water would
cause formation of sludges.
Dirt
Dirt can be introduced into the oil system by
air and while charging in dirty oil. Most of dirt
is introduced into the oil system through the
22
Oil filter
covered
in sludge
air. Very few oil systems and reservoirs have
air filters and if any, efficient air filters. Dirt
particles light enough to float in the air are
drawn into the reservoir every time the oil level
in the tank goes down, by the breathing effect
causing some of the dust particles to settle out
into the oil.
Oil systems and reservoirs with levels that
change frequently can pump many times their
volume of air every hour. This exposes the oil
in the tank to potentially very large amounts
of dirt. This is how new oil delivered from most
oil companies becomes contaminated with dirt
as well.
Additives depletion
Most additive systems are designed to get used
up in service. Monitoring additive levels is
important not only to assess the health of the
lubricant, but it also may provide clues related
to specific degradation mechanisms. Monitoring additive depletion can be complicated and
hard depending upon the chemistry of the
additive component.
The additives present in most oils contain
chemicals that work to extend the life of the
oil. These consist mainly of antioxidants, rust
inhibitors, anti-foam agents, de-emulsifiers, etc.
Water, heat and oxygen, individually or
combined, cause damage to both the base oil
and the additive system. Water reacts with
many oil additives and hydrolyzes them,
denaturing the additive into two or more
chemical fragments. These reaction products
may or may not be oil-soluble and they may act
as catalysts for the further decomposition of
the oil or additives.
Oxygen will react with the additives and
the oil to form oxidation by-products. These
by-products will generally be acidic in nature
at first, and may act as catalysts for further
oxidation.
Oxidation
Oxidation is the reaction of materials especially
hydrocarbons with oxygen in the presence
of heat or high temperature. Oxidation is
the single most negative factor in extending
lubricants life, hence controlling oxidation
is a major challenge in trying to extend the
lubricant’s life.
The process of oxidation is naturally
occurring in the oil, but the rate at which this
happens depends on the following factors:
Lubezine Magazine | July-September 2012