Classify Lubricants As Assets
EP Editorial Staff | April 9, 2020
Oil and grease are assets, not consumables, and should be part of your sustainability program.
By Mark Barnes, PhD CMRP, Des-Case Corp.
According to the U.S. Energy Information Association (US-EIA, eia.gov), the industrial sector accounted for 32% of all energy consumption in 2018, with chemical production, refining, and mining the three largest consumers of energy. While a large percentage of the energy used goes into heating and cooling (AC and refrigeration), a significant portion is used in the form of electricity to provide lighting and power to manufacturing equipment.
Furthermore, in a 2017 study (K. Holmberg, A. Erdemir, “Influence of tribology on global energy consumption, costs and emissions,” Friction 5, 263–284, 2017), researchers from Finland and the U.S. estimated that approximately 23% of energy consumed was in response to “tribological contacts,” of which 20% was used to overcome friction. Since the primary job of a lubricant is to reduce friction, you could argue that lubrication—good or bad—influences as much as 20% of our total energy usage.
The Correct Lubricant
To reduce the amount of energy lost every year due to poor lubrication, there are several simple steps we can take. The first is to select the proper lubricant. Rotating and reciprocating assets ride on a film of oil. That film thickness is based on the lubricant speed, load, temperature, and viscosity. Too low a viscosity and metal-to-metal contact will occur, resulting in wear and frictional losses. If the viscosity is too high, viscous drag will occur, requiring more energy to overcome fluid friction.
However, viscosity is not the only selection criterion. The type of oil can also influence frictional losses. For example, synthetics and other premium lubricants have been shown to reduce energy losses in certain compressors, gearboxes, and electric motors by as much as 4% to 15%. The reduction is due to a combination of increased lubricity from better additive packages and, in particular, the more uniform molecular size of synthetic-based oil molecules that create a lower traction coefficient (less internal fluid friction). This requires less force to move a load supported by an oil film. In applications where there is a high degree of sliding motion, such as multi-stage worm drive, efficiency gains of 6% to 8% have become possible by switching to synthetic lubricants.
Grease selection is also a concern. While selecting a grease with the right base-oil viscosity is just as important as oil-based lubricants, choosing the correct NLGI consistency grade is also a key driver of energy usage. For example, using a multipurpose grease with a base-oil viscosity in the 220- to 320-cSt range incorrectly used to lubricate an electric motor can result in a 4% to 6% increase in force (and hence energy) that the motor needs to overcome, compared with the more normal viscosity of an electric motor grease of 90 to 120 cSt.
While reducing energy or fuel consumption is an important aspect of any lubrication sustainability policy, so too is reducing the amount of oil or grease that is used. Using less oil or grease means less oil production, fewer carbon emissions, and less waste that requires disposal.
Many organizations are moving their asset-management policies toward the ISO 55000 standard first released in 2014, with sustainability as a firm pillar of the standard. In the world of lubrication, ICML (International Council for Machinery Lubrication, Broken Arrow, OK, icmlonline.com) recently launched its own standard—ICML 55—which aligns with ISO 55000 and provides a prescriptive series of recommendations for precision lubrication and lubrication sustainability.
One of the fundamental tenets of ISO 55000 and ICML 55 is the definition of an asset beyond a machine to anything that has tangible value to the organization. By that definition, a lubricant should be considered an asset since the effectiveness of the lubricant can have such a profound impact on equipment life and energy usage. Gone are the days when oil was considered to be a consumable, purchased at the lowest price and changed out on a whim. The health, wellbeing, and cleanliness of the lubricant should be nurtured to extract maximum value from this important asset.
The first step to nurturing your oil is to keep the oil inside the machine by minimizing leakage. Even a leakage rate of a drop per minute can amount to 5-to-10 gallons of oil loss over the course of a year. Multiply that by tens or even hundreds of machines and it becomes clear that oil loss due to leakage can be a major source of a company’s maintenance costs and increased environmental footprint.
In some instances, regulatory bodies such as MSHA (Mining Safety and Health Administration, Arlington, VA, msha.gov) and the ISO 14000 family of environmental standards require that oil usage and losses be tracked. While not all companies or industries are required to track oil purchases and disposal rates, it’s likely that tracking oil usage throughout a plant will become increasingly prevalent with the rollout of stricter environmental policies.
The process of over greasing is also prevalent across all industries. Not only does over greasing induce bearing failure—particularly in high-speed applications—it also results in excess energy consumption as the motor tries to overcome churning and internal friction.
Over greasing, by inference, means that a plant will be buying far more grease than needed to keep equipment running.
Time- vs. Condition-Based
Most OEMs specify an oil-change interval for new equipment. For the large part, these recommendations are very conservative, with good reason. No OEM is going to recommend a two-year (or longer) oil drain if there is even the remote chance that, in doing so, the equipment may fail, resulting in a warranty claim. The old (incorrect) adage that “new oil is cheap insurance” is still held near and dear by many OEMs.
OEM oil-change intervals can often be safely extended by as much as two to five times, provided a quality lubricant is used and the health of the lubricant is monitored. To ensure that oil or grease is fit for continued use, fluid analysis should be used. Critical tests such as acid and base number, oil oxidation, and oxidation potential, as well as additive heath, can all be measured and should be used to change behaviors from time-based to on-condition oil changes.
Online oil-quality sensors can also be effective in helping to time oil changes based on fluid health. Unlike the algorithms used by many automotive manufacturers to signal the time for an oil change, these are actual sensors that use changes in fluid conductivity or permittivity to detect changes in base oil and/or additive chemistry. By monitoring oil health in real-time using a sensor, the data can also be correlated with the operational aspect of the component in question.
The importance of contamination control also cannot be overlooked in extending and optimizing oil drains. Common contaminants, such as particles (particularly catalytic-wear metal particles), water, aeration, and excess oil temperature, affect how quickly a lubricant will degrade. In fact, simply keeping the oil clean and dry can often provide a 50% to 80% time extension in oil life, more than enough to pay for the additional cost of contamination-control hardware. Likewise, a drop in oil temperature of 18 F (10 C) can effectively double the life of an oil.
Environmental awareness, energy reduction, and carbon footprint have become part of the daily lexicon of life. We cannot continue to do the things we did in industry ten or even five years ago. Waste elimination, conservation of precious resources, and good corporate citizenship will all be required as we build more plants and increase production. Next time you change the oil or grease a bearing, think “is there a better or more sustainable way to do this?” Future generations will thank you. EP
Mark Barnes, CMRP, is Senior Vice President at Des-Case Corp., Goodlettsville, TN (descase.com). He has 21 years of experience in the fields of lubrication management, oil analysis, and contamination control and has published more than 150 technical articles and white papers.