What is Condition-Based Maintenance?

Overview

Machines need to be maintained. That’s a fact of life. However, the days of blindly following the old adage “If it ain’t broke, don’t fix it” have come to an end. Manufacturing facilities must take a more proactive approach, called condition-based maintenance, or CBMCondition Based Maintenance. This approach considers the current state of the machine, using that information to make decisions about when and how to work on it.

When organizations use CBM, they don’t arbitrarily perform maintenance just because a certain amount of time has passed. They monitor the machinery and perform maintenance based on its condition. In other words, maintenance is performed only when an impending defect is detected during the monitoring process. Such defects are found through the use of inspections.

Types of Inspections

• Some inspections are performed via the human senses ─ what we can see, hear, feel, smell, and even sometimes taste.
• Others are performed via measurement instruments, such as dial indicators, snap gages, and calipers. Both of these types of inspections fall under what we call preventive maintenanceTime or cycle-based actions performed to prevent system functional failure. This proactive maintenance type generally includes scheduled restoration and scheduled discard tasks. Learn more: What is Preventive Maintenance? (PMPreventive Maintenance).
• Yet another type of inspection is condition monitoring, which falls under the category of predictive maintenanceThe use of instruments and analysis to determine equipment condition in order to predict failure before it takes place so corrective maintenance can be done in a planned and scheduled fashion. Examples include vibration analysis, oil analysis, thermography, airborne ultrasonic’s, NDT, motor current signature analysis, trending of process parameters, etc. (PdMPredictive Maintenance). This refers predominantly to the use of vibration analysisThis Predictive Maintenance technique is widely used to evaluate mechanical rotating equipment to determine if any undesirable changes are present that might give an early indication of imminent failure. Uses transducers to translate a vibration amplitude and frequency into electronic signals to determine the equipment’s actual condition. This may lead to the recommendation of a logical course of maintenance actions to correct the problem before secondary damage or catastrophic failure can occur. Additionally Vibration Analysis can be used for the modeling, prediction, measurement and analysis of structural dynamic response in design and root cause failure analysis. In design, vibration modeling and prediction is used to anticipate and avoid undesirable dynamic response. In root cause failure analysis it is used both to understand undesirable response and as a factor in determining true root cause., infrared thermographyA predicitive maintenance method that detects infrared energy emitted from an object, converts it to temperature, and displays an image of the temperature distribution., oil analysis, motor circuit analysis, and ultrasonic technology.

Why Perform Condition Monitoring?

All maintenance and reliability programs have essentially the same goal: to effectively and efficiently ensure the plant’s production capacity. The best way to accomplish this is by being proactive about dealing with machinery defects. The definition of proactive is to act before the business necessity of the situation demands it; stated another way, proactive means to act before the cost of doing so increases.

If left alone, machinery defects will eventually cause a functional failureThe state in which a physical asset or system is unable to perform a specific function to a level of performance that is acceptable to its owner or user. leading to unplanned downtime. So, the earlier you can detect the defect, the more time you will have to deal with the situation and avoid getting into an emergency state. If an organization can find and fix the defects early enough, the number of emergencies, and the number of schedule interruptions, will decrease drastically.

The Benefits of Condition Monitoring

One of the major benefits of condition monitoring is that the technologies offer an abundance of information about the nature of the defect and, to a large extent, the physical cause of the defect. This knowledge significantly enhances the root cause analysisA systematic approach to problem solving that utilizes a set of techniques to identify physical, human, systemic and latent causal factors. process and eliminates the possibility of this same defect occurring in the future. You could say that the biggest value of condition monitoring is being able to help prevent unexpected failures. It also helps you plan and schedule the outage and, therefore, not experience the surprise of machinery failure when least expected.

Another benefit of condition monitoring is all the data the CBM technologies can provide the maintenance technicians about the nature of the problem. By using some of these technologies, specific defects are identified, such as ‘inner race defects found on both pump bearing,’ instead of the general indication of ‘pump making a strange noise.’ This reduces the troubleshooting time and costs associated with parts swapping until the problem is solved. It also reduces the total amount of downtime for a repair, thus, increasing availability and possibly even productivity.

Condition monitoring assists the planningDetermination of resources needed and the development of anticipated actions necessary to perform a scheduled major job. An orderly appraisal and guarantee of all the prerequisites necessary to ensure completion of a given job at a predetermined time. It covers availability of ordered equipment, stores, materials, production, shutdowns, sketches, prints, specifications, etc. and scheduling process in three ways:

1. It identifies the defects early enough to allow the planning and scheduling process to take its natural flow. Nothing has to be expedited or rushed, and production schedules do not have to be changed at the last minute.
2. It gives the planner something specific to plan. Because of how precise the problem can be pinpointed, the planner can kit a specific collection of parts and have confidence that the required parts are there; and the maintenance technicians will not have to stop the job to go find what they need.
3. Early detection of the fault means that more parts can be ordered, and fewer parts must be kept in stock.

The below chart illustrates how PdM detects problems early and lowers repair costs dramatically.

The nature of the fault progression is that the longer the defect remains, the more quickly it gets worse; thus, it is a curve and not a straight line. The defect gives off different signals along the way, and the different PdM technologies are well suited to identify these signals as they change. These signals help us identify the general location of the defect along its progression path. Knowing this helps with understanding the severity of the defect and allows you to schedule your maintenance accordingly.

Conclusion

From our experience with CBM, we have found that Implementing a solid condition monitoring program brings countless results that impact your bottom line. For example:

• Maintenance costs reduced by 50%
• Unexpected failures reduced by 55%
• Repair and overhaul time reduced by 50%
• Spare parts inventory reduced by 30%
• Mean time between failures (MTBFMean Time Between Failure) increased by 30%
• Machinery availability increased by 30%

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Allied Reliability collaborates with clients to set up condition monitoring programs to move in the direction of CBM.