How Oil Degrades

When oil is used in a machine, the oil will degrade slowly during use over a period of time, depending on the type of lubricant, operating temperature, operating conditions and the physical environment. Lubricant degradation has negative effects on system lubrication and for example, hydraulic system pressures; these problems can result in serious consequences for the equipment performance and reduce reliability leading to breakdowns.

New lubricants are a formulation of base oil and chemical additives. Lubricant additives are present to counteract the majority of ill effects that contaminants cause.

Oil Refiners (Shell, Exxon-Mobil, etc.) produce base oils that can be categorised into groups which gives an indication of its oxidation characteristics. Where longer life is required, Group II, Group III and Group IV base oils are used by lubricant manufacturers. The Group of oil used is determined by the Original Equipment Manufacturers’ recommendations to satisfy the OEM requirements for equipment service and warranty purposes.

Lubricant additives play a critical role in preventing lubricant degradation. The additives are essentially sacrificial in their role of protecting the base oil because the additives will degrade first while minimising any degradation to the base oil molecular properties.

After additive content is consumed by operational forces, the integrity of the hydrocarbon base oil becomes compromised because it is no longer protected by additives. At this point lubricant oxidation and the consequent ‘tell-tale’ discolouration commences.

In short, the modern lubricant has been designed and formulated to meet the harsh operating environment of modern equipment. Contaminants can “unbalance” the lubricant and can result in less than optimum performance in its duty, increasing equipment damage which can ultimately lead to breakdowns.

Types of lubricant additives include:

· Antioxidants (anti-oxidation)
· Antiwear agents
· Viscosity index improvers
· Rust/corrosion inhibitors
· Demulsifiers
· Extreme pressure additives
· Antifoam agents
· Detergents/dispersants

Additive depletion and oxidation

Antioxidant additives are the key to extending your lubricants’ remaining useful life by significantly limiting lubricant degradation from occurring, but antioxidants are depleted in the process. Being sacrificial, antioxidants deplete first before the base oil begins to oxidise and studies have shown that once 70% of the antioxidant additives in new oil have been depleted, physical changes within the lubricant begin to occur. The resulting lubricant oxidation increases the lubricant viscosity, Total Acid Number (TAN) and the formation of sludge and varnish.

By monitoring the antioxidant content of lubricant, CTG detects additive depletion in advance and prevents lubricant oxidation, thickening and acid and varnish formation.

The additive depletion and oxidation reaction is accelerated by a number of factors, primarily:

  • High operating temperatures
  • Moisture contamination
  • Particle contamination

High Operating temperatures
High operating temperatures in the form of mechanical and thermal energy both produce heat which will accelerate lubricant degradation. Heat generated by operating equipment is unavoidable, but excessive heat will lead to increases in the consumption of antioxidant additives. The rate of lubricant oxidation doubles for every 10°C rise in operating temperature above 100°C.

Moisture contamination
Water contamination adversely affects the lubricants by acting as a catalyst for oxidation and causes rapid additive depletion. Water will react with many oil additives, fracturing the additive into two or more chemical fragments. Water also promotes rusting, corrosion and filter plugging. Common sources of water contamination are heat exchangers and seal leaks, condensation, inadequate reservoir covers and temperature drops that lead to dissolved water becoming free.

Particulate contamination
Particulate contamination occurs in many forms within in-service oil, causing abrasive wear, fatigue and erosion. Additional contamination is evident whenever dirt particles circulate through the system at high pressure and at high speed.

Airborne dirt particle contamination is a major contamination source. Light enough to float in air these particles can be introduced in exposed reservoirs as the oil level goes down. Oil reservoirs with levels that change frequently are most at risk to large amounts of dirt and airborne contamination. This is commonly how new oil delivered from oil companies becomes contaminated.

Particulate contaminated lubricant provides reduced lubricating properties and increases friction that results in heat generation.

During oxidation, polymerisation causes sticky molecular structures, commonly referred to as “sludge”. Sludge is a resinous like substance that is darker in colour and leaves deposits throughout the entire lubrication system. Sludge is often why lubricant will darken during its time in use.

With sludge molecules being microscopic in size, the molecules are not removed by some traditional filter systems. Combined with their sticky molecular structure and corrosive effect, lubricant sludge will directly affect the reliability and efficiency of all systems it is found within.

Oxidation by-products cause more oxidation, starting a cycle where the more by-products are present, the faster oxidation accelerates. Quickly the level of oxidation will reach a point where the lubricant becomes destroyed by a change in its molecular structure and must be replaced with new oil.

Preventing lubricant Oxidation
Rapid lubricant degradation will occur when the additive quantity falls below critical level, at this point the rate of oxidation will increase due to the lubricant not having enough additives to counteract oxidation.

The PROPEL Oil Management process includes monitoring of active antioxidant additive to determine the level of lubricant remaining useful life (% RUL), moisture contamination and particulate cleanliness level.

By lubricant condition monitoring and renewal, additive levels do not deplete below critical levels, preventing lubricant degradation and waste. PROPEL Oil Management will renew lubricant to as good as new specification (or higher) before oxidation occurs, preventing costly lubricant replacement.

PROPEL Oil Management – Professionally Renewed Oil Prolongs Equipment Life.