PerkinElmer OilExpress 4, User Manual

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12 . OilExpress 4 System User's Guide
Degradation Products
Oxidation
Oil exposed to oxygen at elevated temperature will oxidize to a variety of compounds, the
majority of which are carbonyl compounds, including carboxylic acids. Carboxylic acids contribute
to the acidity of the oil, depleting the basic additives present and contributing to corrosion.
Oxidation can also increase the viscosity of the oil. The degree of oxidation is a good indicator of
oil degradation. A rapid increase in oxidation may indicate an overheating engine or depletion of
the antioxidant additive due to an over-extended oil change period.
Oxidative degradation also occurs with petroleum gear and hydraulic fluids.
Nitration
Nitrogen oxides, produced by the oxidation of atmospheric nitrogen during the combustion
process, react with the oil. Nitration increases the viscosity of the oil and is the major cause
of the build-up of varnish or lacquer.
A high nitration value, also known as NOx or nitro-oxidation, indicates an incorrect fuel/air ratio,
incorrect spark timing, excessive loads, low operating temperature or piston-ring blow-by.
Sulfate
Sulfur oxides are produced by the combustion of sulfur compounds present in the fuel. These
oxides react with water, also produced by the combustion process, to form sulfuric acid. The
sulfuric acid is neutralized by the oil’s basic additives, forming inorganic sulfates. A rapid
increase in the sulfate value may indicate the use of a high-sulfur-content fuel, poor
combustion, over-cooling or the rapid depletion of anti-wear additive.
Ester breakdown
Synthetic lubrication oils usually contain a high proportion of synthetic polyol esters. These
esters are susceptible to breakdown in the presence of water and acids (hydrolysis). Ester
breakdown contributes to the acidity of the oil and can result in the formation of crystals of
the base polyol, leading to clogging of filters. Ester breakdown may indicate the presence of
water from condensation caused by low operation temperatures or from a coolant leak.
Additive Depletion
Numerous compounds are added to oils to confer desirable properties. These additives can
be depleted during use, and so monitoring this depletion can provide a warning of impending
lubricant failure.
Anti-wear
Anti-wear additives, such as di-alkyl or di-aryl dithiophosphates (ZDDPs) prevent direct
metal-to-metal contact by forming a coating on metal surfaces activated by frictional heat.
These can be depleted by hydrolysis or oxidation, resulting in increased wear rates. A rapid
loss of anti-wear additive may indicate excess loads or contamination by water from a
coolant leak.