It's well known that billions of dollars are lost each year due to unscheduled downtime and poor asset quality. In a never-ending battle to combat this statistic, organizations implement one of a variety of types of maintenance, often combining two or more. Definitions of the types of maintenance vary across the industry, which can make it rather confusing to differentiate things like preventive and predictive maintenance, among others.
Most types of maintenance fall under two main categories: preventive and corrective. Preventive maintenance is when you proactively initiate tasks and maintenance plans to prevent failures from occurring. In addition to preventing failures, preventive maintenance can have the goal of minimizing the consequence(s) of failure or determining the risk of the failure happening.
Corrective maintenance happens after the failure has occurred. Your team is basically getting the asset back to working order at this point. To clarify, corrective maintenance can be deliberate in the form of a run-to-failure maintenance strategy, which will be discussed below.
Let's examine the most common types of maintenance used across the manufacturing and process industries.
There are a couple of types of maintenance that fall within the preventive maintenance category. These include:
For an in-depth look at the types of preventive maintenance, how to design a preventive maintenance program, preventive maintenance tools and more, check out the link at the beginning of this section.
Although many organizations employ both predictive and preventive maintenance (76 percent use preventive, while 65 percent use predictive, according to a recent Reliable Plant survey), there are a few key differences. Most notably, preventive maintenance does not require the condition monitoring aspect that predictive maintenance does. This means predictive maintenance utilizes condition-based technologies like infrared thermography, acoustic monitoring, vibration analysis and oil analysis. Another key difference is preventive maintenance involves inspecting and performing maintenance on assets regardless of whether the equipment needs maintenance (the maintenance schedule is based on a trigger). Predictive maintenance does not.
Below is a chart showing how condition-based maintenance relates to predictive and proactive maintenance. Here, predictive maintenance is one of two sides stemming from CBM: a proactive side that focuses on finding the root cause of a failure and a predictive side that concentrates on the failure symptoms and faults.
For more details on predictive maintenance, predictive maintenance technology and more, click the link at the beginning of this section.
Reliability-centered maintenance is sometimes confused with preventive maintenance, but there is one key difference: preventive maintenance isn't selective like RCM, making it less efficient. Since RCM looks at each asset individually, inefficiency is reduced by assigning maintenance tasks tailored to each piece of equipment.
Reliability-centered maintenance uses a general four-step workflow: Choose the asset, evaluate the asset, determine the type of maintenance and repeat the process. Assessment criteria for implementing an RCM program asks seven questions:
Click the link at the beginning of this section to read more about reliability-centered maintenance, including how to implement RCM, real-world case studies from organizations that have implemented an RCM program, and more.
Total productive maintenance is considered more of a process than a program as well as an operations improvement process rather than a full-blown maintenance program. It's also not a quick fix, as it takes years to achieve a maximum benefit from a high-quality TPM process; however, you can see results immediately.
Total productive maintenance incorporates lean manufacturing and the 5-S System techniques from its internationally accepted benchmark made up of eight pillars: autonomous maintenance, focused improvement, planned maintenance, quality maintenance, early equipment management, training and education, safety, health and environment, and TPM in administration.
Implementing TPM involves five phases:
Click the link at the beginning of this section to read more about TPM, including the eight pillars of TPM, how to implement it, how to sustain a TPM process and more.
Autonomous maintenance has two core principles: to prevent equipment deterioration through proper operation and bringing equipment to and keeping it in "like new" condition through restoration and proper management. This requires operators to master skills such as detecting abnormalities by understanding the machine's components, making improvements, identifying quality issues and figuring out what caused the quality issues.
Implementing autonomous maintenance involves seven steps: increasing operator knowledge, initial machine cleaning and inspection, removing the cause of contamination and improving access, developing standards for lubrication and inspection, inspecting and monitoring, standardizing visual maintenance, and continuous improvement.
For a more in-depth look at autonomous maintenance, how to implement it and how to sustain it, click the link at the beginning of this section.
The caveat to RTF maintenance is it requires good judgment. Knowing when to label something a wholesale failure instead of repairing it is part of the skill set that comes with RTF maintenance. It can present some risk since assets are not being monitored, causing the organization to stare down the barrel of unplanned downtime when something breaks.
However, when implemented on the right assets with smart planning for dealing with inevitable failures, RTF can save time and money by not replacing unbroken equipment.
When it comes to maintenance types, techniques and cost, the primary types of maintenance can be compared with the human body to get a snapshot of the equivalent "body maintenance" task. The table below uses a power-generation asset example and compares it with the human heart.
Maintenance triggers can be set and used with multiple types of maintenance. Breakdown triggers are used with run-to-failure or reactive maintenance plans. Predictive maintenance uses things like time-based triggers in the form of alerts to try and prevent a failure from occurring. Other triggers that will be discussed include event-, usage- and condition-based triggers.
Breakdown triggers typically are only useful when an organization is running a group of low-cost, easy-to-replace equipment and has replacement parts and units in stock which can be readily and easily swapped, minimizing downtime as much as possible. Using breakdown triggers is similar to a cat-and-mouse game; not having to plan for maintenance allows for a less expensive maintenance budget, but it also means you must have spare parts and equipment available at all times, as well as personnel to fix issues. Holding stock like this goes against lean principles like Just in Time (JIT), which are designed to cut down on held stock.
Just like your car gets an oil change every 5,000 miles, any machine that performs time- or quantity-restricted operations can be set up with a usage-based trigger. Meter readings can be added to a CMMS and used to set alerts when a desired quantity or value is reached. Usage-based triggers are a great way of maintaining equipment subject to irregular timetables and are most often used with predictive or preventive maintenance programs.
Equipment condition can be assessed remotely as well. Sensors placed on an asset to monitor parameters such as temperature, vibration and noise can be used as condition-triggered alerts. For example, if a sensor notices a spike in temperature that surpasses a predetermined range, an alert is sent to schedule an inspection.
One of the biggest keys for manufacturers to excel in operational maintenance is to use the data provided by modern technology. To do this, a new maintenance solution is all but required to keep assets, employees and processes organized and working seamlessly.
Technological advances are most prevalent in condition-based monitoring in the form of proactive and predictive maintenance. Under these types of maintenance, technologies like oil analysis, vibration analysis, thermography and motor current analysis can help determine root causes and failure symptoms, seek benefits like machine life extension and early fault detection, and reduce the number and impact of failures.
Today's technological revolution in the manufacturing industry has led to fewer errors and defects, optimized production and reduced labor costs. Automated sensors that can continuously monitor machinery are among the biggest improvements. Not only can they be employed across multiple types of maintenance, but they can also generate a massive amount of data that can be analyzed and used to improve processes.
CMMS solutions can help harness all this data and integrate it with four key aspects for a modern maintenance technology strategy: using predictive maintenance, focusing on data and the IoT, managing inventory, and improving cycles for continued success.
The IoT is employed to wirelessly integrate data gathered from assets on the plant floor to a CMMS utilized throughout the organization. This will require setting previously discussed triggers and alerts to automatically create work orders without human interaction.
While still an emerging trend, using AR for training is gaining in popularity due to the increasing complexity of industrial equipment. Augmented reality can ease the burden on maintenance personnel trying to keep up with variations in new equipment, including technologically advanced capabilities that accompany each asset. There are already several vendors who offer large-scale AR solutions for maintenance tasks and IIoT providers who provide AR as part of a bundled package.
Early stages of MaaS programs are starting to be made available by vendors. ThyssenKrupp Elevators now come with a proactive maintenance program that predicts problems before they occur and notifies the appropriate individuals to perform an inspection. BMW is also planning to take MaaS to the consumer in the near future, offering programs that will let car owners know the best time to have maintenance done on their vehicles.