Historically, machine condition monitoring and predictive maintenance activities have been very sectarian in nature. Researchers and practicing engineers alike have maintained a one-dimensional approach to the business of machine condition assessment.
In industrial applications, especially in the power generation and petrochemical industries, vibration analysis has been the technique of choice. Conversely, in the fleet industries, oil analysis has been the technique of choice because of the preponderance of diesel engines. In general industrial applications such as primary metals, pulp and paper, etc., both have been used, but oil analysis has failed to reach its full potential.
In the industrial (nonfleet) applications of machinery condition monitoring, we have experienced in the past a split between oil analysis and other modes of condition assessment or predictive maintenance, with respect to both the responsible department and the purpose for acquiring the information. Vibration analysis and several other technologies typically have resided within the maintenance department where decisions about ensuring machinery reliability are made. Oil analysis has resided within the lubrication group or the chemistry department where decisions about making oil changes are made.
This is changing. Many plants have found significant synergistic opportunities to increase reliability and uptime when oil analysis is administered by the reliability organization and coordinated with other condition assessment activities. The following discussion explains the unique contributions of oil analysis. The mutually reinforcing roles of oil analysis and vibration analysis in assuring machinery reliability will be covered in a future article.
Oil analysis in machine condition monitoring
The role of oil analysis has a varied and inconsistent history. In the petrochemical and power generation industries, oil analysis has been conducted primarily to determine when and/or if an oil change is required. In hydraulic applications, it has been used to control the contamination that jams servo-valves and abrades components, leading to premature component failure. In fleet applications, oil analysis has been applied to determine when additives have depleted, soot is building up in the oil, fuel and/or coolant is contaminating the oil, or abnormal component wear is occurring. Each application is valid and each application provides information to support important, but varied, decisions. In sum, there are three distinct categories, or dimensions, of oil analysis:
1. Fluid health analysis—Oil analysis reveals the general health of oil. The oil’s physical, chemical,and additive properties can be measured and trended to guide decisions about if and when an oil should be changed or regenerated with an additive package. Oil analysis also identifies when the incorrect oil has been added to a system. When oil is degrading abnormally, oil analysis often can determine if the degradation is oxidative, hydrolytic, or from another root cause. In addition to simple oil change decisions, oil analysis supports decisions to change oil base-stock or additive formulation or control the environment in which the oil operates. Machines cannot run healthfully without healthy lubrication, making these decisions imperative to the reliability effort.
2. Contamination monitoring—Contamination is a leading cause of machine degradation and failure. Abrasive particles and moisture combined lead to the generation of the majority of wear in various industrial applications. Also, particles and moisture contamination strip the oil of its additives and exacerbate lubricant degradation. Contamination monitoring enables the reliability organization to make effective decisions to control this important cause of machine failure.
3. Wear debris detection and analysis—When a machine is ailing, it generates particles. The detection and analysis of wear debris assists in scheduling maintenance actions and in determining the root cause of a problem.
An effective program of oil analysis should include a focus on each of the three distinct dimensions of oil analysis. Relying upon oil analysis information simply to guide oil change decisions leaves a tremendous amount of information value on the table about the machine’s health and the interface between the machine and its environment.
Proactive control of machine health
Avoiding machinery failure should be the prime directive of the reliability organization. Once a machine is specified, designed, manufactured, installed, and deployed, there exists a finite number of variables to ensure health. Production management defines load via production schedules. The reliability and maintenance department has control over the following failure root causes that are known to lead to machine degradation:
Precision alignment and balance programs have proven to reduce the
occurrence of failure. Likewise, controlling lubricant quality and contamination has proven to be very effective in extending the life of mechanical components and systems. In a study by the Canadian National Research Council, contamination was found to be the leading cause of wear in a variety of industries investigated. In fact, 82 percent of all wear was found to be particle induced (see accompanying table).
The effects of contamination are slow and usually imperceptible until the late stages of failure. The result, however, is very predictable. Particle contamination or water contamination can reduce the life of mechanical components by orders of magnitude. In laboratory studies at Oklahoma State University, the British Hydromechanics Research Association, and others, component life was found to be a predictable function of lubricant contamination.
Nippon Steel reduced bearing failures by 50 percent through aggressive contamination control. International Paper’s Pine Bluff mill reported a 90 percent reduction in bearing failures through aggressive contamination control.
In another study, Alumax of South Carolina reported a per-machine reduction in component replacement costs from $15,000 per year to under $500 per year, more than a 96 percent reduction. The Alumax figures do not include the softer labor and downtime costs that always accompany a failure.
The point is that aggressive contamination control improves the reliability of mechanical equipment. But, while the proactive maintenance activities of alignment and balance monitoring assurance are typically the domain of the reliability division, the related activities of contamination control are often left out of check.
The SKF Bearing Co. states that the three “silent assumptions” of bearing life are proper alignment, proper temperatures, and contamination control. The monitoring and control of contamination should take its rightful place in the reliability assurance process and organization.
Improving decision effectiveness with oil analysis
The other principal objective of a condition-monitoring program is to improve the quality of maintenance and operations decisions. These decisions are primarily machine oriented rather than lubricant oriented. The oil carries important information about the machine in the form of wear debris. Wear debris represents the reciprocal of the machine’s surface. By analyzing the metallurgy, morphology, size, color, and relative population of different wear mechanisms, the skilled analyst can often reach the following conclusions:
When proactive and decision support objectives are combined, oil analysis yields tremendous value through the extension of machine life and improved operations and maintenance decisions.
Oil analysis is a reliability function
Having identified the strategic importance of oil analysis for machine condition monitoring, the need to integrate it within the reliability organization, and the importance of on-site oil analysis, a tactical plan is required. While it is not feasible in many instances to install a fully capable on-site oil analysis laboratory, it is possible to implement an economic, streamlined on-site oil analysis program. As earlier stated, there are three distinct objectives in oil analysis: ensure the lubricant is fit for continued service, maintain contamination at acceptable levels, and detect and analyze abnormal wear. These objectives can be met with the following simple field tests:
These simple tests are sufficient to support the needs of the machine condition monitoring team in most instances. Further analysis may be required on an exception basis. For instance, if an increasing wear rate is occurring and the root cause cannot be effectively deduced with the simple on-site tests, the samples may be submitted to a wear debris analysis laboratory for further inspection. Additionally, occasional analysis of the fluid’s chemistry is suggested to estimate the remaining useful life of a fluid and to schedule oil changes and reconditioning. The accompanying flow diagram maps out the strategy for integrating on-site tests, the samples may be submitted to a wear debris analysis laboratory for further inspection. Additionally, occasional analysis of the fluid’s chemistry is suggested to estimate the remaining useful life of a fluid and to schedule oil changes and reconditioning. The accompanying flow diagram maps out the strategy for integrating on-site screening tests with the services provided by a full oil analysis laboratory.
When the three objectives of oil analysis are properly combined, and the program is conceived to provide the right information at the right place and time, oil analysis will improve the life of mechanical equipment and improve the quality of operations and maintenance decisions. The information generated from all condition assessment programs must be effectively combined to optimize the decision process. Analyzing machine condition is often a matter of reading between the lines. This is especially true when hunting for the root cause of a problem. Just as a carpenter goes to the job site with all the necessary tools to complete the job, the reliability technician must carry a full toolbox in his business of making and supporting effective decisions. It is clear that oil analysis is a natural ally of other machinery condition assessment technologies in the pursuit of machine reliability.
The effective integration of oil analysis with vibration analysis and other assessment technologies will be discussed in a future article. MT