Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/490438
www.machinerylubrication.com | March - April 2015 | 23 misidentification of the lubricant(s) in question. Please note that while the latest glycols derived from butylene are far more compatible with mineral oils than those using propylene and ethylene, the analysis of these new glycols is still evolving. This should be taken into consideration when evaluating oil analysis data from a glycol-based lubricant system. Missing or wrong additives can lead to many potential problems. It is common to see a missing extreme-pressure (EP) or anti- wear (AW) additive in gear, bearing and hydraulic applications. If you are missing one of these additives and the equipment requires it, excessive rubbing wear and severe sliding wear could occur, depending on the toler- ances and workload. These additives physically separate the loaded surfaces when the lubricant viscosity is insufficient, and without them you will be contacting these loaded surfaces. If a lubricant with a detergency additive is put into a system designed to shed water, the detergency additive will ruin this shedding property of the lubricant. Generally, the only solution is to remove and completely replace the lubricant or risk having water ingression cause significant bearing wear. This problem is most common when dealing with large turbine sumps that have been contaminated with diesel engine oil. Consider that as little as a quart of diesel engine oil can destroy the demulsibility of 2,000 gallons of turbine oil. If a system with yellow metal (copper alloys) has a manufacturer's recommendation to not use an EP additive, this is usually because the EP additive would be highly corrosive to the yellow metals when the addi- tive reaches activation temperatures. In these instances, a metals test should be conducted to reveal the problem. This test can detect additives and allow you to see changes in the additive levels. Oxidation or nitration tests may also be helpful. In addition, you may be able to identify an incorrect additive with an infrared spectrum comparison/overlay. With this test, two lubri- cants can be overlaid on a single graph to determine if there are any chemical signature differences in the infrared signal. This is not a typical test and should be viewed as an excep- tion test in most cases. For these types of issues, the common recommendations will include using exception testing (analytical ferrography, etc.), which can reveal the extent of surface degradation if there are wear problems. Another recommendation would be to check the manufacturer's specifi- cations as well as the operating temperatures and how they relate to the lubricant selection. The more widespread issue with an incor- rect lubricant involves using the wrong viscosity. If the viscosity is too high, you may see increased wear in gear systems due to reduced or no splashing ability (if the system requires splash lubrication). In hydraulics, a high viscosity can lead to slow performance and low filtration rates. In nearly all low-vis- cosity situations, the result will be elevated wear. This is because the fluid film is not thick enough to prevent surface-to-surface contact during operation. To detect a viscosity problem, perform a viscosity test. Also, consider conducting a base- line test on the new lubricant, as viscosities can change from batch to batch, and a lubricant top-up using a similar lubricant with a different viscosity may not be readily apparent. In addi- tion, you may be able to identify this issue with metals testing, since additive levels will commonly fluctuate along with a viscosity change, even within the same product line. The recommendations for viscosity prob- lems can be fairly involved. This is because along with the possibility of having put a lubri- cant with the wrong viscosity into a machine, there may have also been an operating change that has affected the machine and caused the issue. For example, if the ambient temperature has increased, the viscosity may now be too low for the operating temperature, and wear may start to occur. Outside of this possibility, the most common recommendation will be to change the oil in the sump. If the sump size is signifi- cant, it may be suggested to sweeten the oil or drain off a portion and replace it with fresh lubricant to improve the viscosity. Please keep in mind that these are only a small portion of the problems that may arise and that laboratory testing capabilities are an ever-changing field. New technologies and improved methods are constantly becoming available. If you have a specific issue that requires testing, contact your oil analysis lab and be sure to get the best, most effective testing you can find.