Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/704613
urbomachinery is synonymous with highly productive equip- ment, high costs and high volumes of lubricant usage. For this reason, lubricant contamination control is critical for the reliable operation and long life of these machines. A good contamination control strategy not only will identify potential contami- nants but also determine their source and establish methods to control and measure them consistently. Defining cleanliness targets or maximum concentration levels will be important in selecting the appro- priate contaminant removal approach. This article will discuss common contaminants that can be present in turbomachinery, such as solid particles, water, air, heat and varnish, as well as strategies that can be implemented to control them. Solid Particles Solid particles can originate from the machine's environment, be produced inter- nally from the machine's operation or be introduced into the machine during assembly, commissioning or maintenance activities. These particles can be harmful based on their size, hardness, weight and angularity. They may create abrasion in sliding surfaces as well as surface fatigue (pitting) in rolling contacts. Very small particles (less than 5 microns) can even cause components to stick when tolerances are narrow, such as in servo valves. Solid contaminants can also generate more particles as a result of machine wear. Depending on their composition, these types of contaminants can be monitored by different means. Particle counting is the most representative test for measuring the pres- ence of solid particles. Results are generally reported based on the ISO 4406 standard. For metallic particles, elemental anal- ysis, ferrous density testing or a patch method can be employed to observe parti- cles with a microscope. Elemental analysis and a patch method can also be utilized for non-metallic particles. Organic particles (insoluble suspensions) can be character- ized with Fourier transform infrared (F TIR) spectroscopy. Be sure to define your cleanliness targets and discuss them with the original equip- ment manufacturer (OEM). You must also consider contaminant exclusion or elimi- nating the root causes of contamination. This involves the actions required to clean and preserve the lubricant before it goes into service as well as the modifications and procedures to keep the machine's lubrication system isolated from contami- nation sources. These actions include proper filtration. A centrifuge can also help eliminate high concentration levels of contaminants (e.g., free water, dirt and wear debris). Finally, don't forget to eliminate contaminants that ingress into the in-ser- vice lubricant during normal operation. This can be achieved through similar methods and by using the filtration systems installed on the machine. Water Water contamination may come from a variety of sources, including simple condensa- tion of atmospheric moisture. In turbomachinery, water can produce rust and corrosion, impede oil film production, accel- erate adhesive wear, and cause vaporous cavitation. Within the in-service oil, water can lead to acid formation, increased foaming, entrained air, base oil hydrolysis and additive water washing (depletion mechanism). It is also a contributing factor to the formation of sludge and varnish. Water contamination can be measured in the field with inexpensive instruments, such as a crackle test or a calcium hydride kit. In the laboratory, the coulometric Karl Fischer method deploying co-distillation may be used to reduce the risk of additive interference. Again, the best strategy must involve contaminant exclusion and removal. Effec- tive methods for removing water include vacuum dehydration, decantation (purging free water) and centrifugation. A good STRATEGIES for T C o n t a m i n a t i o n C o n t r o l Contamination Control TURBOMACHINERY BACK PAGE BASICS a l e Ja ndro me z a | Nori a Corpor at ioN 54 | July - August 2016 | www.machinerylubrication.com 48% of MachineryLubrication.com visitors use turbomachinery in their plants, according to a recent survey