Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/468007
34 January - February 2015 | www.machinerylubrication.com ASK the EXPERTS Critical equipment most defi nitely should be checked more frequently than non-critical equipment. Based on the defi nition of "critical," you are referring to the machines with the highest importance to you, your company and your process. These assets deserve the focus of your limited time, money and energy. Of course, it is important to know how you defi ne an asset as critical. There are many approaches to determine the criticality of an asset. Some plants choose to use a simple 1 to 5 grading scale and subjectively assign numbers, while others utilize large, drawn-out processes and even employ a coaching consultant to help make the determination. However, the decision can be narrowed down to a few key attributes: impact on production, impact on safety, impact on the environment, replacement cost, spares or redundancy availability, probability of failure, historical data on reliability and preventive maintenance. Most plants are very limited in manpower and money. If there are only so much of these resources in your "bank," you want to be sure to spend them wisely. In order to make an informed decision on how to spend, you must have a good grasp of the assets' criti- cality relative to one another. These criticalities can also be used to help set work prioritiza- tion. With limited resources, you always want to be working on the highest priority jobs fi rst. This ranking of jobs is all but impossible if you don't have an understanding of machine criticality. Oil sampling is a good example of using criticality to drive scheduling decisions. Any asset that has a high impact on produc- tion, safety and the environment; costs more to replace; has little to no spare parts or redundancy; coupled with a high failure prob- ability and poor reliability and preventive maintenance would be an excellent candidate for real-time, continuous online monitoring. As the asset's attributes become less and less severe, the sampling frequency relaxes, changing from continuous monitoring to maybe hourly, daily, monthly, quarterly or annually. You may even reach a point where you decide that oil analysis just doesn't offer any benefi t because the machine has little to no impact on production, safety or the environment. It might be cheap to replace, or you may have easy access to spares. Criticality is very much a part of making informed decisions on scheduling, whether it be a simple sight-glass inspection or as complex as a turbine rebuild. "Should critical equipment be checked more often than non-critical equipment?" "What role does density play in the overall performance of lubricants, especially in regard to hydraulic oil?" Density is a key property not only in lubricants but in all fl uids. It is the measure of the mass of a substance in relation to a known volume. For example, the density of water is 62.4 pounds per cubic foot. However, this varies according to the temperature of the fl uid. Lubricants generally are less dense than water. If the density of an object is less than that of water, then that object will fl oat. This is why if you have a moisture problem in your lube system that the water settles to the bottom of the sump and is drained out fi rst whenever the plug is pulled or the valve is opened. This value is also used in some calculations involving viscosity. Viscosity is the single most important property of a lubricant, so if any math is to be done using this value, the density must be known. A common conversion between absolute viscosity to kinematic viscosity uses the density value. If the density of a fl uid changes for whatever reason, this can introduce errors in converting between