Condition based maintenance (CBM)
Condition based maintenance (CBM) is a maintenance strategy that monitors the actual condition of the 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 scheduled 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 preventative maintenance, this increases the time between maintenance repairs, because maintenance is done on an as-needed basis.
The goal of condition based maintenance is to 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, this lowers disruptions 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
- Optimized 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.
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.
Types of condition based maintenance
- Vibration analysis – rotating equipment such as compressors, pumps, 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 – measure 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 to measure pressure, temperature, flow etc.
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 inflight 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 suffice.
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 techniques to do maintenance, 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.