Condition-based maintenance (CBM)
Condition-based maintenance (CBM) is a maintenance strategy that monitors the actual condition of an asset to decide what maintenance needs to be done. CBM dictates that maintenance should only be performed when certain indicators show signs of decreasing performance or upcoming failure. Checking a machine for these indicators may include non-invasive measurements, visual inspection, performance data and scheduled tests. Condition data can then be gathered at certain intervals, or continuously (as is done when a machine has internal sensors). Condition-based maintenance can be applied to mission critical and non-mission critical assets.
Unlike in planned maintenance (PM), where maintenance is performed based upon predefined scheduled intervals, condition-based maintenance is performed only after a decrease in the condition of the equipment has been observed. Compared with preventive maintenance, this increases the time between maintenance repairs, because maintenance is done on an as-needed basis.
What’s the goal of condition-based maintenance?
The goal of condition based maintenance is to monitor and spot upcoming equipment failure so maintenance can be proactively scheduled when it is needed – and not before. Asset conditions need to trigger maintenance within a long enough time period before failure, so work can be finished before the asset fails or performance falls below the optimal level.
- CBM is performed while the asset is working, which lessens the chances of disruption to normal operations
- Reduces the cost of asset failures
- Improves equipment reliability
- Minimizes unscheduled downtime due to catastrophic failure
- Minimizes time spent on maintenance
- Minimizes overtime costs by scheduling the activities
- Minimizes requirement for emergency spare parts
- Optimizes maintenance intervals (more optimal than manufacturer recommendations)
- Improves worker safety
- Reduces the chances of collateral damage to the system
- Condition monitoring test equipment is expensive to install, and databases cost money to analyze
- Cost to train staff–you need a knowledgeable professional to analyze the data and perform the work
- Fatigue or uniform wear failures are not easily detected with CBM measurements
- Condition sensors may not survive in the operating environment
- May require asset modifications to retrofit the system with sensors
- Unpredictable maintenance periods
Example of condition-based maintenance
Motor vehicles come with a manufacturer-recommended interval for oil replacements. These intervals are based on manufacturers’ analysis, years of performance data and experience. However, this interval is based on an average or best guess rather than the actual condition of the oil in any specific vehicle. The idea behind condition based maintenance is to replace the oil only when a replacement is needed, and not on a predetermined schedule.
In the example of industrial equipment, oil analysis can perform an additional function too. By looking at the type, size and shape of the metal particulates that are suspended in the oil, the health of the equipment it is lubricating can also be determined.
Types of condition based maintenance
There are various types of condition-based monitoring techniques. Here are a few common examples:
- Vibration analysis: Rotating equipment such as compressors, pumps and motors all exhibit a certain degree of vibration. As they degrade, or fall out of alignment, the amount of vibration increases. Vibration sensors can be used to detect when this becomes excessive.
- Infrared: IR cameras can be used to detect high-temperature conditions in energized equipment
- Ultrasonic: Detection of deep subsurface defects such as boat hull corrosion
- Acoustic: Used to detect gas, liquid or vacuum leaks
- Oil analysis: Measures the number and size of particles in a sample to determine asset wear
- Electrical: Motor current readings using clamp on ammeters
- Operational performance: Sensors throughout a system measure pressure, temperature, flow etc.
Challenges of condition-based maintenance
- Condition-based maintenance requires an investment in measuring equipment and staff up-skilling so the initial costs of implementation can be high.
- CBM introduces new maintenance techniques, which can be difficult to implement due to resistance within an organization.
- Older equipment can be difficult to retrofit with sensors and monitoring equipment, or can be difficult to access during production to spot measure.
- With CBM in place, it still requires competence to turn performance information from a system into actionable proactive maintenance items.
CBM = Cost Savings + Higher system reliability
Condition-based maintenance allows preventive and corrective actions to be scheduled at the optimal time, thus reducing the total cost of ownership. Today, improvements in technology are making it easier to gather, store and analyze data for CBM. In particular, CBM is highly effective where safety and reliability is the paramount concern such as the aircraft industry, semiconductor manufacturing, nuclear, oil and gas, et cetera.
Data can be collected from the system by two different methods:
- Spot readings can be performed at regular intervals using portable instruments
- Sensors can be retrofitted to equipment or installed during manufacture for continuous data collection
Critical systems that require considerable upfront capital investment, or that could affect the quality of the product that is produced, need up-to-the-minute data collection. More expensive systems have built in intelligence to self-monitor in real time. For example, sensors throughout an aircraft monitor numerous systems while in flight and on the ground to help identify issues before they become life-threatening. Typically, CBM is not used for non-critical systems and spot readings will suffice.
The bottom line
When carried out correctly, condition-based maintenance is a minimally disruptive form of maintenance that lessens overhead costs, risk to workers, and downtime due to unexpected breakdowns. Maintenance managers should be aware, however, that setting up a CBM program can be costly, and the changes required to set up the strategy could be met with resistance or confusion. At the end of the day, this strategy requires a great deal of expertise to analyze the data and condition information presented.