Temperature affects how oils and greases perform and should be considered as part of a plant’s overall lubrication strategy.
The biggest impacts of temperature are on viscosity and lubricant life, which determine how well the equipment is lubricated, the energy needed to overcome friction and drag (especially at startup), and the frequency with which lubrication changes are needed.
In indoor applications, peak temperature is set by the equipment’s operating conditions. Oils and greases should be selected to provide dependable performance over this range. In outdoor and uncooled indoor environments, temperatures fluctuate, and lubricants may need to operate over a much wider span.
Cold Weather
Low temperatures increase viscosity, meaning the oil flows less readily. Every oil has a “pour point,” which is the lowest temperature at which it will flow under gravity; oils should be selected where the pour point is at least 18, and ideally 36, degrees below the minimum expected.
When viscosity is higher, oil appears thicker and requires more force to pump, increasing startup loads and energy use. Higher viscosity also means surfaces may contact before the oil forms a lubricating film, causing scuffing and wear.
Condensation can form in storage tanks and reservoirs when the air temperature drops, leaving moisture on tank walls that can run into the oil, potentially causing corrosion, increasing scuffing risk, forming an emulsion that clogs delivery pipes, or freezing.
Using Lower Viscosity Grades or Softer Greases
Switching to a lower viscosity can help reduce flow problems during cold starting. Viscosity is often specified using the ISO Viscosity Grade system, where a VG of 100 is equivalent to an SAE 30 grade, and VG 22 is equivalent to SAE 5W.
ISO grades are calculated based on viscosity at 104°F, and viscosity is higher at lower temperatures, so choose oils with a high viscosity index and a low pour point.
For greases, look for softer grades that will remain more flexible in the cold. For example, switch from NLGI #2 to NLGI #1.
Switching to Synthetic Base Oils
Many lubricating oils are mineral oil-based, and these become increasingly viscous as temperatures fall. However, synthetic base oils such as polyalphaolefins (PAOs) retain fluidity better at lower temperatures and have a high VI, so viscosity declines slowly as temperature rises.
Preheating/Process Heating
Heating equipment before startup at low temperatures warms and lowers the viscosity of oils and greases, reducing startup loads and the time it takes to form a lubricant coating on metal surfaces.
Increasing Water Evaluation
A crackle test quickly checks for water contamination, though it lacks sensitivity at low moisture levels. A more sophisticated approach is Karl Fischer water titration, as detailed in ASTM D6304.
Desiccant Breathers
Desiccant breathers absorb moisture that would otherwise enter storage tanks and reservoirs, helping reduce contamination, icing, and corrosion caused by condensation.
Hot Weather
A general rule of thumb is that every 18°F rise in temperature halves oil life.
At high temperatures, oil becomes thinner and oil films may break, allowing scuffing and increasing wear. High temperatures also increase the rate at which oil oxidizes, which reduces its effectiveness and life. Oxidation can also cause gums and resins to form that can increase friction and drag.
High temperatures can also permanently change oil composition as lighter additives vaporize. Oil condition monitoring is a useful tool for detecting lubricant degradation.
With grease, high temperatures can lead to separation and bleeding.
Using Higher Viscosity Grades
Moving to a higher ISO Viscosity Grade can be an effective solution, but it may also increase startup loads. Instead, use oils with a higher VI that flow more consistently across a wider temperature range.
For grease, switching to a higher NLGI rating can achieve similar results.
Shorter Drain Intervals
In hot weather, it’s advisable to change the oil more frequently to reduce oxidation in the system. However, for maximum benefit, the system should be flushed before the new oil is added.
A disadvantage of this tactic is increased downtime and higher maintenance costs.
Using Oxidation-Resistant Base Oils
Standard mineral oils often have poor oxidation resistance. Some formulations include oxidation-resistant components, but this only slows the inevitable, though it can extend the time between oil changes.
Synthetic base oils, such as PAOs, resist oxidation better than mineral oils. Consider switching to these for high-temperature applications.
Oil Cooling & Heat Exchangers
An alternative to using oils and greases that tolerate high temperatures is add cooling circuits and heat exchangers to lower the oil temperature. This solution may require additional pumps and valves, and heat exchangers in ambient air are of limited value in hot weather because they rely on a temperature differential for heat flow. To achieve useful cooling, some form of refrigeration may be required.
Increasing Reservoir Size
A larger oil reservoir can help circulating lubrication systems handle hot weather. The increased mass of oil reduces the heating effect of hot oil returning to the tank and raises the thermal capacity of the system. Oil also stays in the tank longer, giving it more time to lose heat before it’s pumped back out to the lubrication points.
Need Help With Your Strategy?
Lubrication strategies should address specific operating patterns, working practices, and the environment where the equipment is used. A key part of a lubrication strategy is identifying thermal patterns and determining effective ways to work with them.
Indoor equipment can suffer from high temperatures and the effects of hot weather, but the thermal challenge is potentially far more severe for equipment used outdoors.
DropsA has been a pioneer in lubrication technologies since 1946. Today, in addition to our extensive range of oils, greases, and lubrication equipment, we provide consulting services to help plants optimize equipment life and performance.
Contact us today for product recommendations, configuration assistance, or help with determining the best lubrication strategy for your application.
