Condition-based Maintenance: A Complete Guide

Jonathan Trout, Noria Corporation

Condition-based maintenance (CBM) is a maintenance strategy that monitors the real-time condition of an asset to determine what maintenance needs to be performed.

Condition-base maintenance  

What Is Condition-based Maintenance?

Condition-based maintenance (CBM) is a maintenance strategy that monitors the real-time condition of an asset to determine what maintenance needs to be performed. Unlike preventive maintenance, which uses things like calendar-based maintenance or other means to determine when to schedule and perform maintenance, condition-based maintenance dictates that maintenance should only be done when these real-time indicators show irregularities or signs of decreasing performance.

The goal of condition-based maintenance is to continuously monitor assets to spot impending failure, so maintenance can be proactively scheduled before the failure occurs. The idea is that this real-time monitoring will give maintenance teams enough lead time before a failure occurs or performance drops below an optimal level.

Condition-base maintenance vs PdM

Using sensors and spot readings are the most common ways real-time data is collected for analysis. For example, sensors can be installed on a piece of rotating equipment to monitor its vibration. Over time, as the moving components degrade and begin to fall out of alignment, vibration increases, which is picked up by the sensors. The installed sensors can be preset to alert the maintenance team when vibrations reach a determined limit.

While condition-based maintenance can be used on most equipment, that equipment must meet certain criteria for CBM to be effective. First, there needs to be a monitorable condition. In other words, if the performance of the machine can't be measured, how can you tell if there's a change in performance? You also need to be able to see changes in performance far enough in advance, so maintenance can be performed before the asset fails or lessens in production.

Asset criticality is another criterion you should consider before utilizing condition-based maintenance. You'll get the best return on investment (ROI) using CBM on your most critical assets. Doing a criticality analysis to rank which pieces of equipment are most likely to fail and the impact that failure will have on your operation is a vital step before performing condition-based maintenance. It's important to scale from the most critical assets down.

Finally, condition-based maintenance is only as effective as the processes and systems used to analyze the data. Maintenance teams must be able to collect performance data and analyze it properly to make smart and timely decisions based on the results.

 

Types of Condition-based Maintenance

One of the biggest advantages of condition-based maintenance is that it is non-invasive, meaning real-time data is being collected while the machine is still running without adjusting the way it operates. You can choose to collect data at certain intervals or continuously through things like sensors, visual inspection or scheduled tests. Let's take a look at some of the most common types of condition-based monitoring techniques used in CBM.

Types of condition-based maintenance
  • Vibration analysis. Vibration analysis is defined as the process for measuring vibration levels and frequencies of machinery and using that information to analyze the health of machines and their components. Vibration analysis can help detect problems like imbalance, bearing failure, mechanical looseness, resonance, bent shafts and more.

    A simple example might look like this: Imagine you have an industrial fan. You remove one of the fan blades and start it up. As you might expect, the fan starts to vibrate due to the unbalanced fan wheel. This imbalanced force will happen one time per revolution of the fan, producing increased vibration signals. You could also have a damaged bearing track causing a bearing roller to generate vibration each time it contacts the spall. So, if three bearing rollers hit the spall per revolution, you'd see a vibration signal three times the fan's running speed.

  • Infrared thermography. Infrared thermography is the process of using a thermal imager to detect radiation coming from an object, converting it to temperature and displaying an image of the temperature distribution in real time. Often utilized with a baseline image for comparison, infrared thermographic images can clearly and easily show when an asset is becoming overheated. Infrared thermography is employed for monitoring the electrical and mechanical conditions of motors, inspecting bearings and examining refractory insulation, as well as for checking gas, liquids and sludge levels.

    Infrared tools include spot infrared thermographers, which are used to measure thermal radiation on hard-to-reach assets or assets operating under extreme conditions; infrared scanning systems, which scan larger areas or objects on a conveyor belt; and infrared thermal imaging cameras, which measure temperature at multiple points across a large area and create two-dimensional thermographic images.

  • Ultrasonic analysis. Ultrasonic analysis uses sound to identify potentially failing assets by detecting high-frequency sounds and converting them into audio and digital data. Data collection methods determine the types of detectable failure when it comes to ultrasonics. You can either have contact (structure-borne) or non-contact (airborne) methods. Contact methods generally are used for mechanical issues like bearing faults, lubrication problems, gear damage and pump cavitation. All of these faults emit a high-frequency noise. Ultrasonic contact methods are also helpful for detecting electrical faults on motors, as loose or broken rotor bars can generate a high-frequency, rhythmic pattern. Lastly, steam traps that are failing may have steam constantly leaking past the internal seals, causing a rattle, which is picked up with ultrasound.

    Non-contact methods (airborne) of ultrasonic measurements include pressure and vacuum leaks on compressed gas systems and a number of electrical applications. Air surveys use ultrasonics to detect leaks in compressed gas systems. When it comes to using airborne ultrasonics for electrical systems, ultrasonic methods can detect arcing and corona when thermography can't.

  • Oil analysis. Oil analysis is a routine activity for analyzing oil health, contamination and machine wear. An oil analysis program helps verify a lubricated machine is operating as it should. Oil analysis checks the oil's fluid properties, answering questions like are the right additives active. Have additives depleted? Is the viscosity where it needs to be? Oil analysis also looks to see whether there are destructive contaminants in the oil and, if so, helps narrow down the probable source. Lastly, oil analysis lets you analyze the presence of particles produced from mechanical wear, corrosion or other machine surface degradation.
  • Electrical analysis. Electrical analysis is employed to examine the incoming power quality of assets using motor current readings from clamp-on ammeters to measure the current in a circuit. This makes it easier for maintenance personnel to see when an asset is getting an abnormal amount of electricity.
  • Pressure analysis. Maintaining the correct pressure within equipment to let fluid, gas or air move through a pipeline or hydraulic hose properly is vital. Pressure analysis can continuously monitor pressure levels in real time and alert to sudden drops or spikes, allowing maintenance personnel to respond to and fix issues before a more serious incident occurs.
 

Steps to Take Before Implementing Condition-based Maintenance

As touched on earlier, there are certain things you can do to get the most out of a condition-based maintenance plan.

Steps for implementing condition-based maintenance
  1. Ensure a solid foundation. Condition-based maintenance goes hand-in-hand with reliability-centered maintenance (RCM) because RCM helps you identify potential problems with your assets and determine what you should do to make sure those assets continue producing at maximum capacity. Having a solid grasp of RCM processes helps to focus your condition-based maintenance efforts where they need to be. In fact, reliability experts agree that one of the biggest issues that comes with adopting a condition-based maintenance program is the lack of understanding of RCM principles.
  2. Include affected personnel. Once you've established that all maintenance personnel have the necessary skills, include them in the criticality analysis. Incorporating their input makes them active participants and gives them the opportunity to use their RCM fundamentals effectively while contributing to the condition-based maintenance implementation. It also will help them to identify, mitigate and eliminate failure modes.
  3. Perform criticality analysis. As briefly mentioned earlier, a criticality assessment ensures your condition-based maintenance program is effective. Accurately identifying assets as critical, semi-critical and non-critical can decrease unnecessary route-based maintenance. In other words, maintenance personnel will know which assets are most critical and can perform checks on those assets first or more often than non-critical assets without making needless routes all over the plant.

    Criticality analysis also helps determine which assets will benefit most from condition-based monitoring techniques like remote vibrations or acoustic sensors that produce real-time data which can be analyzed from another location. These more critical assets are referred to as "bad actors" or the repeat offenders in your asset lineup. These bad actors benefit more from continuous monitoring since they tend to have frequent issues. Keep in mind, once you've completed a criticality analysis, it's not uncommon to find that the assets you once considered critical are not as critical as you previously thought.

  4. Follow up. After you've finished your criticality assessment, it's a good idea to implement a failure reporting, analysis and corrective action system (FRACAS) to ensure your analysis was correct and the most critical assets are benefiting the most from your condition-based maintenance program.
 

Implementing Condition-based Maintenance: IAEA Example

In May 2007, the International Atomic Energy Agency (IAEA) recognized the need to begin moving nuclear power plants from a preventive (time-based) maintenance program to a condition-based maintenance program dependent on plant and component conditions. Upon recognizing this need, the agency developed and standardized how to implement a CBM program in a publication entitled, Implementation Strategies for Condition-based Maintenance at Nuclear Power Plants. The outlined strategies use various online and offline condition monitoring techniques to define how to select components and parameters for monitoring, which monitoring and diagnostic techniques should be employed, how to incorporate acceptance criteria and more.

The IAEA's primary objectives for this condition-based maintenance strategy include improving availability by reducing forced outages; enhancing equipment life by decreasing wear from frequent rebuilding; detecting problems as they occur; minimizing the potential for problems in disassembly and reassembly; and saving on maintenance costs by reducing repair costs, overtime and parts in inventory.

The IAEA's condition-based maintenance strategy consists of a combination of visual inspection and continuous monitoring techniques on things like pressure boundary components, containment structures, main turbine generators and reactor coolant pumps. For example, this could involve online diagnostics used in turbine generator thrust bearing wear monitoring. Suggested condition-based maintenance technologies include vibration monitoring, acoustic analysis, motor analysis, motor-operated valve testing, thermography, tribology and process parameter monitoring, all coupled with visual inspections.

The IAEA found the challenge of switching to a condition-based maintenance program wasn't from the lack of knowledge about advanced technological methods but rather was centered around the willingness to change the culture and management in order to get them on board. Understanding this challenge, it focused its CBM implementation process around four elements:

  • Commitment - The maintenance staff must commit to the process and its new technology. It has to trust the training and technology, while management needs to commit to procuring adequate equipment and training for all staff.
  • Participation - To achieve success, 100 percent participation in the CBM program is required from all groups. This expectation must be reinforced by management.
  • Holistic approach - This applies to all systems throughout the plant with no exceptions.
  • Sustainability - The CBM program, staff and equipment must be maintained over time to reap the long-term benefits. As people come and go from the organization, the proper training and resources need to be available.

To ensure CBM implementation was properly portrayed to maintenance staff, IAEA recognized the need for effective communication and training. It outlined the following thought process for educating a nuclear plant and explaining the basics of the CBM process: conditions analyzed, methods chosen, methods implemented and project evaluation. Each of these can be broken down by asking "what," "why," "how" and who."

  • Conditions analyzed: This includes the criticality analysis.
    • What? – Ensure management commitment, identify needs, look at ambition and expectations, identify available resources, etc.
    • Why? – Understand the overall view of what is needed.
    • How?– Site visits, evaluation of company performance.
    • Who? – Experts and authority figures/owners.
  • Methods chosen: This is where CBM methods and roles are decided.
    • What? – Choose the roles and needs of the CBM team; identify and select methods.
    • Why? – To select methods that fulfill all needs found in initial analysis.
    • How? – Consensus of the leaders and maintenance team.
    • Who? – Anyone affected by the CBM implementation.
  • Methods implemented: This is where discussion is put into action.
    • What? – Roles are developed. Ensure all plans and projects are communicated and understood by performing training, getting IT support, etc. Create benchmarks.
    • Why? – To improve maintenance and reliability as quickly as possible.
    • How? – On-the-job training, coaching project meetings and follow-up.
    • Who? – Project manager, maintenance team and anyone else affected.
  • Project evaluated: This includes analysis of the newly implemented CBM process to ensure everything is working as planned.
    • What? – Follow up on the goals of the CBM plan, discuss experiences, and lay out a plan for administration and development.
    • Why? – To ensure the CBM is working as intended.
    • How? – Audit and meeting for follow-up and planning.
    • Who? – Process owners, management and leaders.
 

Challenges of Condition-based Maintenance

So, what's the catch? As with any process change or new process implementation, condition-based maintenance comes with some challenges.

Challenges of condition-based maintenance
  • Significant initial cost. The upfront costs associated with CBM tend to add up as you perform a criticality analysis and figure out where you need to place sensors. This can be even more costly if you must retrofit them on older assets. This is partly why your criticality analysis is so important, because it determines which equipment will give the highest ROI. Newer or smaller plants might not have the onsite expertise to perform this kind of analysis, so it's wise to bring in an expert to conduct a failure mode and effects analysis (FMEA) and an RCM analysis, which will be an additional cost.

    Also, choosing the proper sensor is critical. Consider factors like operating conditions, as sensors built to withstand harsh operating environments generally cost more.

  • Training. Now that you have sensors to provide real-time data and insight into the equipment's condition, you must have personnel who can analyze this data properly and quickly. For each fault detection or alert produced by a sensor, multiple questions arise. Does a part need to be replaced? Is the part in stock? How long do we have before the asset fails? Do we need the vendor to do the replacement?

    Keep in mind, training is another expense and involves pulling operators and other maintenance staff away from their normal operating duties. Training also involves getting everyone on board with the change and effectively managing the change. As learned from the IAEA, this is one of the most difficult parts of implementing a condition-based maintenance program.

  • Operating conditions. The accuracy and performance of your sensors partly depends on the environment in which they are functioning. Harsh operating conditions can lead to malfunctioning or damaged sensors. For example, high heat and humidity can affect electronics, while corrosive chemicals can damage sensors and yield inaccurate readings.
  • Unpredictability. Unlike scheduled maintenance, maintenance work based around a condition-based monitoring program is unpredictable. For instance, you may perform maintenance when a sensor alerts you. This can cause irregularity in how costs appear in your budget. For example, if a handful of assets require maintenance at the same time, your maintenance team must be able to manage the repairs quickly.
  • Software requirements. Each installed sensor collects massive amounts of data continuously, so it's important to have a modern computerized maintenance management system (CMMS) or other software that can organize, track, collect and analyze this data. Along with having the right software, you'll need to consider hiring a third party to help analyze the results until your staff is fully trained.

    Additionally, make sure your Wi-Fi connection can handle the amount of data being used and your cloud storage plan is large enough to hold the stored data.

 

Benefits of Condition-based Monitoring

With all the challenges that come with implementing a condition-based maintenance program, you may be wondering if it's worth it. While a CBM program isn't cheap initially and can take some time to get up and running, you eventually can receive a lot of value from it. Once implemented correctly and run by a well-trained staff, it can lead to many benefits, such as:

  • improved system reliability,
  • increased productivity,
  • lower maintenance costs,
  • a decrease in downtime,
  • quicker problem diagnosis, and
  • a reduction in the time between maintenance.

A CBM program's potential for a high ROI appeals to many organizations due to the fact that it can help them remain competitive and operate as lean as possible.

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