Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1475671
6 | July - August 2022 | www . machinerylubrication.com 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. According to ASTM D7155, the mixtures must go through a short bedding-in time at an elevated temperature. is allows the base oil and additives to chemically and physically interact, after which the mixtures are ready to be inspected and tested further. If floc, sedi- ment, 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, a sequence of additional testing tiers will be required. e exact tests and passing conditions associated with these supplemental tiers must be thought through carefully (lubricant, application and exposure dependent). Machine criticality plays a vital role in this decision, along with other factors. A lubricant specification can be used as the baseline for the supplemental tests, or the performance listed on the new lubricant from its product data sheet can be used. However, a well-con- structed specification is necessary for critical applications. Example performance tests can include filterability, air-handling ability, water-handling ability, film strength, oxida- tion stability, corrosion suppression, etc. e selection of tests for the supplemental tiers is largely driven by service life needs (of the oil) and the critical performance needs in the target machine application. Again, standardized test methods can be employed, especially relating to elastomers and surface treatments. e risks relating to chemical exposures might include certain gases (refrig- erants, ammonia, hydrogen sulfide, etc.), fuel, coolants, process chemicals, etc. Custom or modified standardized testing may also need to be performed to assess their compatibility. Developing an Oil Drain and Flushing Strategy For obvious reasons, a changeover is strongly discouraged if incompatibility is found (or there is uncertainty) between the new backup lubricant and the machine (seals, for instance) or the operating environment (e.g., process gases) (see Figure 1). If a change- over is still unavoidable, seek other lubricant options to mitigate the risks and consequences. Do not underestimate the importance of this. Should incompatibility only be found between the lubricant mixtures (not the machine or operating exposures), a change- over can usually be successfully performed. However, this requires special precautions, such as the complete removal of the previous lubricant and the decontamination of sedi- ment, sludge and varnish. e greater the danger, the more rigorous the drain and flushing procedure should be. We can relate this to the definition of risk, which is the probability of a compatibility problem multiplied by the consequences of incompatibility. High lubricant incompati- bility (determined from testing) relates to the probability of a problem occurring, and high machine criticality defines the consequences of failure (lubricant and/or machine). Criticality includes such things as the cost of repair, lost production, the cost of flushing and safety risks. Where the danger is the highest, 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. ese 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. e displacement fluid is sacrificial and, as such, needs to be completely compatible with the final fluid charge and relatively inex- pensive. 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 (high Reynolds Number) gives the best results. Many independent companies offer flushing services that are worth considering. Greatest Changeover Dangers If machine surfaces fail to clean completely, a chemical flush may be required. is can be added to the displacement fluid at a concen- tration of 5%-10%. 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 intro- duced. is is typically done with yet another displacement fluid. Rigorous Post-changeover Monitoring After the f lush has been completed and the final oil charge added, combat the law of unintended consequences by using a post-changeover monitoring strateg y. Accelerate oil analysis and other machine inspections (foam, cloudy sight glasses, high temperature, discoloration, noisy operation, etc.) — test for foaming tendency and demul- sibility 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. ML About the Author Jim Fitch has a wealth of "in the trenches" experience in lubrication, oil analysis, tribology and machinery failure investigations. Over the past two decades, he has presented hundreds of courses on these subjects. Jim has also published more than 200 technical articles, papers and publications. He serves as a U.S. delegate to the ISO tribology and oil analysis working group. Since 2002, he has been the director and a board member of the International Council for Machinery Lubrica- tion. He is the CEO and a co-founder of Noria Corporation. Contact Jim at jfitch@noria.com. AS I SEE IT START YOUR FREE SUBSCRIPTION www.machinerylubrication.com