- Buyer's Guide
In the interest of reducing purchasing costs and streamlining storage and handling, many organizations have substantially slashed the number of lubricant SKUs (stock keeping units) they use. They have also re-engineered the precision of their lubricant specification. There are many real and a couple of somewhat imaginary benefits to these consolidation initiatives. Let’s start with the real benefits.
Reducing stale inventory by directing more turnover (usage) across fewer lubricant products
Purging discontinued or hard-to-find lubricants from lubricant storerooms
Sole sourcing lubricants to a single distributor and perhaps brand to simplify the purchasing function and leverage volume buying (see figure 1)
Enhance usage convenience and lower risk of accidental cross-contamination (fewer drum pumps, transfer systems, filter carts, top-up containers, etc.)
Re-engineering and enhancing lubricant selection especially for machines utilizing lubricants that have drifted out of spec (perhaps as a result of several past consolidation attempts)
Figure 1. Varying Suppliers Used Across Lubricant Range
The imaginary relates to the false reality that limiting lubricant SKUs to the catalog products of a single major brand can optimize the selection and number of lubricants in typical process industry plants and factories. For instance, some chemical plants have reported as many as 80,000 lube points, all requiring periodic relubrication. Many of these same companies have bloated inventories of lubricants from as many as 25 brands of more than 200 unique products. These are the companies that stand to benefit the most from consolidation.
Of course, along with the potential for benefits and savings, there are also many real risks and concerns. Most of these are associated with cutting corners and failing to do proper lubrication engineering. This can be avoided by making technically sound decisions with the support and advice of qualified lubrication advisors. Some lubricant suppliers have these capabilities, but others do not. After all, one or two harsh machine failures from placing the wrong lubricant in a high-value machine can wipe out all the potential savings and benefits that might have otherwise been realized.
How mistakes can be made:
Mixing Incompatible Lubricants - This occurs when doing a rolling change-over to a new lubricant that is incompatible with the lubricant previously used and still in the machine. A rolling change-over is periodically adding make-up fluid on top of a previous lubricant of a different type or brand. The mistake is failing to check compatibility and failing to fully drain and flush where required.
Machine-Incompatible Lubricants - In certain cases lubricants (additives or base oils) can actually attack machine surfaces and lead to sudden-death failures. Areas of risk include chemical sensitivity to machine metallurgy, seals, coatings, filters and other nearby lubricants that may come into contact with a new lubricant.
Under-qualified Lubricants - In an effort to reduce costs and pare down the number of lubricants in use, there is the temptation to use an inferior (inexpensive) lubricant in a machine or to force-fit a lubricant that is of good quality but sharply off-specification (compared to the needs of the machine). This may seem harmless at first, but can cost dearly in the long run. This should never be done with critical machines.
Any time a machine is disturbed by changing the lubricant (drain and fill) there is risk, even when using the same exact lubricant. This includes routine oil changes and regreasing practices. Changing a lubricant is an invasive process done by a human being capable of error. When a completely different lubricant is applied, the risk is magnified due to the unknowns of how the machine might respond (Murphy’s Law stuff).
Of course, efforts to enhance reliability and reduce maintenance costs always involve some degree of change or intervention. Change is necessary. The trick is de-risking the situation by avoiding rash decisions and other common mistakes.
Below are a few risk mitigation strategies:
Be fully aware of machine criticality. Changing the use or specification of lubricants in mission-critical equipment should not be done without skillful engineering. Consider OEM specifications/warranties, industry standards and guidelines, and the wisdom of experts and professionals in the field. If lubricant changes are made, mitigate the risk by doing frequent and thorough post-change condition monitoring (wear debris, vibration, temperature, acoustics, motor current, etc.).
Avoid the common practice of consolidating viscosities. While changing a viscosity up or down one ISO viscosity grade will not likely result in imminent failure, there may still be a high cost paid. Wrong viscosity is the most common mismatch of a lubricant to a machine. Wrong viscosity is the source of excessive friction and energy consumption, increased sensitivity to particle contamination, lubricant starvation problems, lubricant air-handling problems and loss of film strength. Instead, when going through the consolidation process, take the opportunity to get the viscosity correct by going back to lubrication engineering fundamentals (bearing speed factors, etc.). Consider temperature and loading extremes as well as base temperature averages. Over the long run, tweaking the viscosity a little more toward optimum can sharply enhance reliability and reduce energy consumption. Remember there is a 50% difference in viscosity going from one ISO viscosity grade to the next higher grade.
Avoid the temptation of over-using a multi-purpose lubricant, especially in machines that have unique demands and would benefit the most from precision lubrication. Multi-purpose lubricants are for machines that are generally low-duty, non-process-critical and historically, very reliable. Conversely, machines that run at loads and speeds exceeding rated loads and can cause process interruption on failure should not use general-purpose lubricants.
The basic approach to lubricant consolidation is for non-critical machines and where there is minimal deviation from machine lubricant specification.
Follow these steps:
1. Group lubricants for basic consolidation based on generic type and performance (e.g., for instance ISO VG 32 turbine oils would be one group and ISO VG 460 EP Gear Oils would be another group).
2. For machines currently using lubricants from the same group (ISO VG 32 turbine oil for instance) select a single lubricant of suitable robustness based on volume of use and brand performance (see figure 2). Robustness relates to such things as oxidation stability, film strength, viscosity index, demulsibility, dispersancy, etc.
Figure 2. Lubricant Robustness Versus Volume of Usage
3. De-risk machines selected for switch-over based on compatibility between the old lubricant and the switch-over lubricant. Compatibility needs to be verified.
Select machines for the advanced approach based on factors such as criticality, lubricant cost and consumption, and robustness demanded by machine and application. When in doubt, use the advanced approach. The advanced approach requires the involvement of someone with specialized skills/training in lubrication engineering.
This is how it works:
1. Develop a technical lubricant specification for each machine according to machine type, operating conditions, exposures, OEM recommendations/warranties, and need for reliability. If a technical specification already exists, review it for completeness and engineering integrity. The specification should have a narrative section that fully describes the lubricant requirement and a data section that lists minimum/maximum physical and performance specifications (see figure 3).
Figure 3. Example of Technical Lubricant Specifications
2. Group specifications from individual machines based on similarity; differentiated only by robustness
3. Select one or more specifications from each group based on robustness, current volume of use, and expected price (see figure 4). From the figure you can see the volume of use in the green area is more balanced between robustness demanded by the machines and applications. In such case, two turbine oils might be selected (A and B) to cover the range of need. For machines represented by the plant in the orange area, the robustness demanded by the machines is skewed to the left (mild robustness). For this plant the best choice might be two turbine oils A and C. Most of the machines would get oil C with the rest getting the more robust oil A.
Figure 4. Lubricant Robustness Versus Usage Differences Between Two Plants
4. As with the basic approach, de-risk machines selected for switch-over based on compatibility between the old lubricant and the new switch-over lubricant. Compatibility needs to be confirmed by testing.
5. After the switch-over monitor machines carefully for any change in operating conditions (leakage, hot-running, noisy, vibration, etc.)
Consolidation sometimes results in force-fitting an over-qualified lubricant (high robustness) into an application where a lower lubricant would do just fine. This does not always result in throwing money out the window. For instance, if a premium synthetic lubricant has exceptional oxidation stability, then extending drain intervals can go a long way to recoup the added cost. So too, a lubricant with enhanced film strength might substantially extend machine rebuild intervals. An excellent job of lubricant consolidation requires a significant investment in time and engineering resources up front. I’ve listed the many potential benefits that can be gained including lower costs and enhanced machine reliability. The financial impact of these benefits can be substantial.
Most importantly, the decisions that result from lubricant selection give a process plant one of the few areas of real control relating to operating costs and total equipment utilization.