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It goes without saying that lubricants aren’t indiscriminately interchangeable, even if they are in the same product class. This is especially true with industrial lubricants, and there are very few exceptions. From experience, we’ve learned that lubricant change is too often the precursor to sudden and unexpected machine failure.
Don’t get me wrong. Noria is all about challenging the status quo and promoting change. While change brings the potential for considerable opportunity, it also can introduce considerable risk. This is probably where the adage “if it ain’t broke, don’t fix it” originated. The opportunity is what we seek, and fortunately when it comes to a lubricant changeover, we have considerable control over the risk.
Lubricant brand or type changes should always be viewed as machine and system disturbances. Never forget the lessons of Murphy’s law: “Anything that can go wrong will go wrong.” Therefore, make sure you have a compelling reason for a change, such as:
A lubricant brand change refers to switching product brands but not the product type, e.g., going from oil supplier A to oil supplier B for the same product (like a Group II turbine oil). A lubricant type change is typically the result of consolidation or performance enhancement initiatives. For instance, switching from an AW 46 mineral hydraulic fluid to an AW 46 synthetic hydraulic fluid would be a product type change. In this article, the term “changeover” will be used to represent one or the other.
If a change is highly desired or simply inevitable, then a good strategy is to get a firm grasp on the potential risks. Fortunately, the industry has considerable experience from which to draw understanding and plan risk management. Most changeover problems are associated with the following:
However, some lubricant changeovers offer much milder risk concerns. These include cases where:
When the risk has been assessed to be low, then a rolling changeover is usually acceptable. This is nothing more than periodically using the new lubricant for top-ups (makeup fluid). The changeover can be accelerated by doing a bleed-and-feed. Even in relatively low-risk circumstances, it is important to implement post-changeover monitoring practices, which will be discussed later.
Conversely, the highest risk changeovers are frequently associated with:
There are numerous industry standards that provide guidance on compatibility testing (ASTM, FTC, etc.). The typical protocol (e.g., ASTM D7155) involves preparing binary mixtures of the lubricants with questionable compatibility. Mixtures such as 50:50, 95:5 and 5:95 are often used, but this can be modified to better match the target application.
After a short bedding-in time at an elevated temperature, which allows the base oil and additives to chemically and physically interact, the mixtures are ready to be inspected and tested further. If floc, sediment, clouding or discoloration develops from the mixtures, the lubricants are confirmed to be incompatible (tier-one test) without further analysis. If this doesn’t occur, then another tier of testing should be seriously considered.
Machine criticality plays a vital role in this decision, along with other factors (see sidebar on page 4). A lubricant specification can be used as the baseline for the tier-two tests, or the performance listed on the new lubricant from its product data sheet. Performance tests can include filterability, air-handling ability, water-handling ability, film strength, oxidation stability, corrosion suppression, etc.
The selection of these tier-two tests is largely driven by the critical performance needs in the target machine application. Again, standardized test methods can be employed, especially relating to elastomers and surface treatments. Risk relating to chemical exposures might include certain gases (refrigerants, ammonia, hydrogen sulfide, etc.), fuel, coolants, process chemicals, etc. Custom testing may also need to be performed to assess their compatibility.
For obvious reasons, a changeover is strongly discouraged if incompatibility is found between the new lubricant and the machine (seals, for instance) or the operating environment (e.g., process gases) (see Figure 1). If a changeover is still unavoidable, seek other lubricant options to mitigate the risks and consequences.
Should incompatibility only be found between the lubricant mixtures (not the machine or operating exposures), a changeover usually can be successfully performed if special precautions are taken. These relate to the complete removal of the previous lubricant and the decontamination of sediment, sludge and varnish.
|57%||of lubrication professionals consider unsatisfactory historic performance to be the most compelling reason for a change in lubricant brand or type, based on a recent survey at machinerylubrication.com|
The greater the danger, the more rigorous the drain and flushing should be. We can relate this to the definition of risk, which is the probability of a compatibility problem times the consequences. High lubricant incompatibility (determined from testing) relates to the probability of a problem occurring, and high machine criticality defines the consequences. Criticality includes such things as the cost of repair, lost production and safety risks.
Where the danger is high, drain the system completely of all remnants of the previous fluid. Look for trapped cavities of fluid in heaters, coolers, off-line loops, hoses, filters, low-point traps, line extensions, etc. Even after the drain is complete, oil will still occlude to the internal machine surfaces. These wet surfaces along with the presence of sludge and surface deposits (including varnish) are high risk.
Follow the drain with a displacement or chase fluid to carry away the remaining previous oil. The displacement fluid is sacrificial and as such needs to be completely compatible with the final fluid charge and relatively inexpensive. A low-viscosity base oil is sometimes used or perhaps even a transformer oil. Heating the displacement fluid and passing it through all internal fluid zones at high velocity gives the best results. Many independent companies offer flushing services that are worth considering.
If machine surfaces fail to clean completely, a chemical flush may be required. This can be added to the displacement fluid at a concentration of 5 to 10 percent. One common product sold by DuBois Chemicals is Step-One cleaner (also branded and available from other lubricant suppliers). It is not a solvent but a calcium-sulfonate detergent product blended in a mineral base oil that has been found to be very effective. One drawback is that this cleaner must be completely removed from the system before the final lubricant is introduced. This is typically done with yet another displacement fluid.
After the flush has been completed and the final oil charge added, combat Murphy’s law by using a post-changeover monitoring strategy. Accelerate oil analysis and other machine inspections (foam, cloudy sight glasses, high temperature, discoloration, noisy operation, etc.). Test for foaming tendency and demulsibility characteristics.
Also, don’t forget to change lubrication procedures to include the new lubricant for top-ups and oil changes. Be sure to re-label the machine with the correct new lubricant as well.
Note: Although this article addresses oil changeovers, grease changeovers present an equally high risk. For information on this topic, visit www.machinerylubrication.com/Read/882/mixing-greases.