Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1222953
52 | March - April 2020 | www . machinerylubrication.com BACK PAGE BASICS Compressors frequently use synthetic lubri- cants based on the OEM's recommendation. Equipment manufacturers often require the use of their branded lubricants as a condition of the warranty. In these cases, you may want to wait until after the warranty period has expired to make a lubricant change. If your application currently utilizes a mineral-based lubricant, switching to a synthetic must be justified, as this often will be more expensive. Of course, if your oil anal- ysis reports are indicating specific concerns, a synthetic lubricant can be a good option. However, be sure you are not just addressing the symptoms of a problem but rather resolving the root causes in the system. Which synthetic lubricants make the most sense in a compressor application? Typically, polyalkylene glycols (PAGs), polyalphaolefins (POAs), some diesters and polyolesters are used. Which of these synthetics to choose will depend on the lubricant you are switching from as well as the application. Featuring oxidation resistance and a long life, polyalpha- olefins generally are a suitable replacement for mineral oils. Non-water-soluble polyalkylene glycols offer good solubility to help keep compressors clean. Some esters have even better solubility than PAGs but can struggle with excessive moisture in the system. Oil Analysis Tests A multitude of tests can be performed on an oil sample, so it is imperative to be critical when selecting these tests and the sampling frequencies. Testing should cover three primary oil analysis categories: the lubricant's fluid properties, the presence of contaminants in the lubrication system and any wear debris from the machine. Depending on the type of compressor, there may be slight modifications in the test slate, but generally it is common to see viscosity, elemental analysis, Fourier transform infrared (FTIR) spectroscopy, acid number, varnish potential, rotating pressure vessel oxidation test (RPVOT) and demulsibility tests recommended for assessing the lubricant's fluid properties. Fluid contaminant tests for compressors likely will include appearance, FTIR and elemental analysis, while the only routine test from a wear debris standpoint would be elemental analysis. An example of oil analysis test slates and alarm limits for centrifugal compressors is shown below. Because certain tests can assess multiple concerns, some will appear in different catego- ries. For example, elemental analysis may catch additive depletion rates from a fluid property perspective, while component fragments from wear debris analysis or FTIR may identify oxidation or moisture as a fluid contaminant. Alarm limits often are set as defaults by the laboratory, and most plants never question their merit. You should review and verify that these limits are defined to match your reliability objectives. As you develop your program, you may even want to consider changing the limits. Frequently, alarm limits start out a bit high and change over time due to more aggressive cleanli- ness targets, filtration and contamination control. Understanding Compressor Lubrication In regard to their lubrication, compressors can seem somewhat complex. e better you and your team understand a compressor's function, the effects of the system on the lubri- cant, which lubricant should be selected and what oil analysis tests should be conducted, the better your chances of maintaining and enhancing the health of your equipment. ML About the Author Matthew Adams is a technical consultant for Noria Corporation, concentrating in the field of predictive maintenance. He has experience in multiple condition-based maintenance technol- ogies and focuses the majority of his attention on lubrication program development, training and general consulting. Matthew holds a Machine Lubricant Analyst (MLA) Level III certification and a Machinery Lubrication Technician (MLT) Level I certification through the International Council for Machinery Lubrication (ICML). Contact Matthew at madams@noria.com to find out how Noria can help you maintain the compressors at your facility. An example of oil analysis test slates and alarm limits for centrifugal compressors.