Extending oil change intervals on heavy mining equipment

There are many hidden costs of an oil and filter change that have influenced companies to find a more efficient approach to keep oil healthy and reliable. 

A recent study found that the true cost of an oil change normally exceeds the oil cost by a factor of 40. These same principles can be applied to filter changes. The following factors contribute to the true cost of an oil change:

• Lost production.
• Paperwork (including maintenance schedules, data entry, manpower planning, inventory management, work orders, documentation, etc).
• Labor and supervision.
• Storage and handling costs, purchasing and quality assurance (additional costs associated with obtaining lubricants must be taken into consideration, such as lubricant storage and handling, filtering new oil to ensure compliance with specifications, analysing oil samples, transportation, disposal of used oil, environmental issues, etc).

Often a lubricant remains serviceable for long periods of time without draining and recharging (influenced by make-up rates, operating temperature, fluid volume, cleanliness, etc). Draining oil and adding new lubricants into a system presents risks such as:

• Introduction of the wrong oil.
• Introduction of contaminants or contaminated oil.
• Re-suspension of settled contaminants in the tank/sump floors and inactive zones.
• Human agency failures (dead-heading pumps on restart, not opening suction lines, not removing cleaning solvents, loosening machine parts, etc.).

Considering the real cost and the associated risk of an oil change, it is wise to let the conditions of the oil drive the decision.

There is an assortment of operating conditions that can reduce the life of lubricants and filters. Obviously, if possible, these are to be avoided. However, very often nothing can be done, as many of the factors are associated with the machine?s application and environment.

The timing of an oil and filter change is important, but even more important is the strategy to proactively improve conditions that extend oil life. When applied correctly, proactive maintenance strategies can double or triple lubricant and filter life. This is achieved by reducing the conditions that stress the oil and filter.

The following is a list of factors that influence the life of a lubricant.

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Contamination control is indispensable in preserving the integrity of all material in power and motion systems. Without it, few if any systems could ever achieve their intended purpose, let alone their expected service lives. Contamination control offers the assurance needed to achieve efficient, reliable and economical production of the ?necessities? and ?amenities? of our modern civilisation.

Knowing the potential and probable sources of contaminants helps to establish an effective exclusion program. Generally, three fundamental modes contribute to contamination:

1. Those injected by people (implanted during manufacturing or induced in the field during maintenance, repair or overhaul operations).
2. Those generated by the systems (created tribologically, chemically or by desorption).
3. Those ingested by the machine (introduced by inhalation of dust, air and water, encroachment of energy and migration of microbes from the environment).

The control of contamination in machinery is pointless if contaminated or below-specification lubricants are used, or if clean lubricant is being handled so carelessly that it enters machines in a contaminated state. Much work should be done in close co-operation with the lubricant suppliers to ensure that clean lubricants of the right specification are used in a particular application.

Inefficient engines contaminated by combustion byproducts including soot, fuel and fuel residuals, sulphur, acids and water. These contaminants distress the quality of the lubricant, resulting in filters going into bypass very quickly.

Worn engines, timing/injector problems, lugging, incorrect rack settings, excessive idling, cold operating conditions and high elevations can all contribute to increase blow-by. This adds soot, fuel and other contaminants that distress even the most robust lubricants.

Glycol and water sharply disrupt dispersancy and contribute to a host of other problems such as corrosion, deposits, filter plugging, etc.

Fuel dilutes additives and introduces sulphur and aromatics into crankcase oils, which will affect viscosity. Lubricant and filter life is influenced by the quality of diesel fuel and natural gas, especially relating to sulphur levels.

Blocked air filters result in the engine being starved. This causes overfuelling, leading to higher levels of soot entering the crankcase oil.

Lugging, stop-and-go driving, intermittent service, cold ambient temperatures, idling, etc, all influence the life of the crankcase oil.

Low oil levels concentrate heat, contaminants and catalytic wear metals, resulting in fewer additives available to resist oxidation and lubricant degradation.

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Dirt and other solid contaminants attract additives and can catalytically advance the rate of oxidation. An even bigger problem is associated with the wear debris that is generated from abrasion and its influence as a pro-oxidant.

Water contamination leads to oxidation, additive distress, loss of dispersancy and many other lubricant life-related problems.

Oil degradation products often contain high concentrations of carboxylic acids, free radicals and hydro peroxides. When oil is drained from a compartment but sludge and varnish remain, the following oil change could be short lived.

Make-up oil refreshes additives and dilutes contaminants. Lube compartments with low make-up rates, while beneficial in one sense, also require more frequent oil changes.

The quality of base oils and additives can have a marked influence on oil life. Some lubricant suppliers can design lubricants with specific characteristics suited for a high or low ambient temperature environment. High operating temperature accelerates the rate of additive depletion and oxidation.

The ingress of other contaminants can degrade additives and affect the quality of base oils. Any fluid system, reservoir or gearbox that is open or connected to the atmosphere by means of a breather inhales and expels air. 

By this action, it ingests moisture and collects water. Humid air exposed to temperature variations in a reservoir constantly condenses water into the system, causing hydrolytic action, corrosion, fluid additive breakdown, etc.

In certain areas, silica gel dryers can be used with synthetic media hydraulic oil filters to remove dirt and moisture from the air. Hydraulic filters are used as breathers. They filter down to at least a 5? (micron) absolute level.

To establish extended oil drain intervals, it is necessary to:

• Construct a fleet profile.
• Estimate oil drain intervals and potential cost savings associated with the optimum oil drain intervals.
• Assess the risk associated with the optimum oil drain intervals.
• Develop a testing plan for a small segment of your equipment to determine if the estimated oil drain intervals are acceptable.
• Implement the optimised oil drain interval after testing.

Fleet profiles describe the equipment, service severity, operating conditions and maintenance practices. Different engine models contaminate engine oil at different rates. The same engine may have a different oil volume in different equipment. Fuel and oil consumption rates vary for different equipment and service severities.

The capability of the oil and the engines must be considered to properly estimate oil drain intervals. Studies show that a litre of fleet oil possesses the ability to neutralise and suspend the contamination generated by burning 300 liters of fuel. High quality premium oils have the ability to neutralise and suspend the contamination generated by burning 500 litres of fuel.

In conclusion, it has been shown how extended service intervals can lead to enormous savings. By using oil analysis and setting target cleanliness levels along with proactive maintenance, a significant downward trend in lubricant consumption and maintenance costs can be achieved. 

The availability of equipment also will increase, allowing for more production, higher revenue and increased utilisation of equipment. 

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