Lubricants are engineered products designed to perform a specific function for specific applications. Whether its the transmission of power, providing lubrication between moving objects, or used in a combustion application, the lubricant is designed to protect the equipment and to some degree manage the contaminants that are inherent to the application. Contaminants act as the catalyst which causes the lubricant to break down and eventually fail. In theory, if all contaminants were controlled within acceptable limits, lubricants could last forever. As with any process, the law of diminishing returns kicks in, and therefore in a manufacturing context its important to identify practical limits that systems need to be managed within in order to balance the Total Process Cost. World Class Manufacturing keeps moving that bar as we work to deliver 100% process performance, 100% on-time, at the lowest cost possible. As technology changes, new methods, techniques, analysis, equipment etc continues to be developed, we have to look for better ways to manage contamination, protect our equipment and extend lubricant life. Condition Management identifies and looks to monitor or control all the KPI's that impact the lubricants ability to deliver on its designed function and also monitor and control the contaminants and their impact on the lubricant itself.
Every lubricant is essentially made up of two elements, the Base Stock and the specialized additive package designed for the application itself. When the base stock and additive package are combined, the product is designed to be within an ISO defined viscosity specification at a defined temperature. Viscosity is a critical characteristic for your lubricant as it determines the acceptable film thickness required for the application. For example an AW68 hydraulic oil must have a kinematic viscosity of + or - 10% measured at 40 Deg C, in order to meet the ISO specification. So as long as the lubricants' measured viscosity is between 61 and 75 cst at 40 deg C, it will provide the desired Film Thickness. If the viscosity changes significantly due to contamination or lubricant degradation, then the film layer will change, increasing the rate at which the process will eventually fail.
Additive packages are specially designed by manufacturers to give the various lubricants their unique properties. Typically additives are sacrificial in nature, meaning they tend to get "used up" over time in the application. Their rate of use can change significantly based on many factors which makes their regular monitoring an important part of ensuring that the condition of the fluid continues to meet specification. An industry rule of thumb is to use 70% as a minimum guideline. So that when the additive levels reach 70% of the level they were at in the virgin state, then there needs to be an additive re-fortification strategy in place, or the fluid needs to be replaced. Often additives are there to deal with the contaminants of the system, and therefore if the rate of contamination can be controlled, then the rate of additive depletion can be dramatically reduced. Additive levels are typically measured through elemental oil analysis, or in some cases their effectiveness is measured through qualitative testing.
TAN: Total Acid Number is used as a predictive measurement of lubricant condition. As the lubricant degrades due to the various contaminants introduced in the process (see Contamination Management), acids begin to build up in the lubricant itself. As the acids build, a certain threshold is reached where the oil itself completely breaks down chemically and fails.
Monitoring TAN therefore is an important part of any lubricant condition management program as its an early indicator of lubricant failure, allowing you to proactively plan the required maintenance.