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13.01.13 Changing Oil Based on Oxidation

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Changing Oil Based on Oxidation

Noria Corporation

Tags: oil oxidation, oil changes, oil analysis

"As oil ages, it oxidizes. What is the bestindicator that the oil has oxidized too much and

should be changed based upon the results given

in a typical oil analysis? We analyze the oil from

our mixer gearboxes and will typically run the

same oil in the gearbox for several years as

long as the oil analysis comes back with good

results."

The first issue here is to define a "typical" oil

analysis. Most labs have several test packagesto choose from that may or may not give an

overall solid feel for lubricant oxidation. In order

to identify lubricant oxidation, it is important to

include oil properties monitoring as part of your

regular test package. This will allow for the

extension of drain intervals based on lubricant

condition as well as help to identify adverse

operating conditions that may exist.

Common tests that cover lubricant properties

include viscosity, neutralization number (acid

number for industrial-based lubricants, base

number for mobile equipment) and FTIR. The values of the results in all of these tests will

increase as the level of oxidation increases (with the exception of base number, which will

decrease as the level of acids increase via the oxidation process).

A couple of common field tests that can help to indicate possible oxidation are darkening color

and foul odor. Oxidation usually has a sour or pungent odor, similar to rotten eggs. It occurs

when the hydrocarbon constituents of lube oil combine chemically with oxygen. As with the

laboratory tests, it is important that sensory testing is compared to that of a virgin oil base

sample.

Just like with most chemical reactions, oil oxidation is accelerated by heat and pressure. It is

no different than other commonly encountered oxidation reactions, such as rusting. Just like

the effects that rusting and other corrosive processes have on metal substrates, oil oxidation

results in a catastrophic and permanent chemical change to the base oil molecules. The net

effect of prolonged oxidation is that the oil becomes acidic (chemically), causing corrosion,

while an increase in viscosity occurs (physically).

Oxidation will generally happen at a slow rate under optimum conditions; however, as the

health of the lubricant decreases, the rate of degradation will increase. There are several otherfactors that, if not controlled, can lead to increased rates of oxidation. These factors include

heat, air, water and metallic particles.

Using a combination of these tests will assist in pinpointing positive levels of oxidation.

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Combined with appropriate equipment monitoring tests and contaminant tests, root causes of

oxidation can also be found and controlled.