9 Types of Maintenance
How to Choose the Right Maintenance Strategy

Across industry, many definitions are used when it comes to the different types of maintenance. It can quickly get confusing when people talk about preventive maintenance, condition based maintenance or predictive maintenance but actually have something else in mind than you do. Some people get very excited about these definitions and can spend a lot of time on for example disagreeing with what is and what isn’t preventive maintenance. Let's not do that, instead, I'll offer you my view of the different types of maintenance and more importantly, when to use them.

Table of Contents
    Add a header to begin generating the table of contents

    9 Types of Maintenance: From Preventive Maintenance to Corrective Maintenance and Everything in Between

    As far as I am concerned terminology is not important. Other than making sure we are talking about the same thing. If what I consider to be condition-based maintenance you call predictive maintenance that doesn’t really matter. As long as we can sensibly talk about the underlying principles.

    When to use condition-based maintenance. And how to use it.

    However, as I’m often asked questions about the different types of maintenance I decided to put a quick overview together of the types of maintenance. At least, the way I see it:

     

    9 different types of maintenance

     

    What are the Types of Maintenance?

    There are 9 Types of Maintenance split between Preventive Maintenance and Corrective Maintenance. Preventive Maintenance is done before a failure occurs and consists of maintenance types like: Time Based Maintenance, Failure Finding Maintenance, Risk Based Maintenance, Condition Based Maintenance and Predictive Maintenance. Corrective maintenance is done after a failure has occurred either as Deferred Corrective Maintenance or as Emergency Maintenance.

    In the rest of this article, I will discuss each of these different types of maintenance I detail:

    Preventive Maintenance

    Corrective Maintenance (CM)

    But before we delve into those definitions, let's have a look at the fundamental difference between preventive maintenance and corrective maintenance.

    types of maintenance pdf

      Preventive Maintenance vs Corrective Maintenance

      At the top level, I see maintenance being either preventive or corrective:

      • When we do preventive maintenance we are doing a task before a failure has occurred. That task can be aimed at preventing a failure, minimising the consequence of the failure or assessing the risk of the failure occurring.
      • When we are conducting corrective maintenance the failure has now occurred and we are basically reinstating equipment functionality. To be clear, corrective maintenance can be the result of a deliberate run-to-failure strategy.

       

      preventive maintenance vs corrective maintenance

       

      Preventive Maintenance

      Preventive maintenance can be defined as “an equipment maintenance strategy based on replacing, or restoring, an asset at a fixed interval regardless of its condition. Scheduled restoration tasks and replacement tasks are examples of preventive maintenance tasks.” 1

      Preventive maintenance (or preventative maintenance) is basically a type of maintenance that is done at a regular interval while the equipment is still functioning with the objective of preventing failure or reducing the likelihood of failure.

      Preventive maintenance can be time based i.e. every week, every month or every three months. But preventive maintenance can also be based on usage e.g. every 150 cycles, every 10,000hrs or like your car: service every 10,000km.

      Apart from the regular interval approach (time based maintenance) there are also other types of maintenance that fall within the category of preventive maintenance:

      In the following paragraphs, I will explore each of these types of maintenance in more detail including when you should consider using them.

       

      Time-Based Maintenance (TBM)

      Time-Based Maintenance refers to replacing or renewing an item to restore its reliability at a fixed time, interval or usage regardless of its condition. This is what Moubray calls Scheduled Restoration or Scheduled Discard tasks in his RCMII book.

      I limit the use of that phrase as for some reason people then jump to the conclusion that another maintenance is not scheduled. When in fact, of course, all maintenance should be scheduled through our Weekly Schedule. The only exception would be Emergency Maintenance, which due to its very nature of requiring immediate attention cannot be scheduled.

      The purpose of Time Based Maintenance is to protect yourself against the failure of known wearing parts which have predictable Mean Time Between Failure (MTBF) i.e. Time Based Maintenance assumes that the failure is age related and a clear service life can be determined. Or, that it’s simply not worth the effort to assess the condition and a time based replacement is more economical and still (reasonably) effective.

      Time Based Maintenance can never effectively manage non-age related failure modes and therefore should only form a small part of your overall maintenance program as >70% of the failure modes in your plant are not age related (refer to the article 9 Principles of Modern Maintenance).

      It is important to realise that in many industries companies do have to complete certain tasks to meet regulatory compliance requirements and these would typically be executed on a fixed time interval i.e. Time Based Maintenance. But even with compliance related maintenance, there are often opportunities to engage a regulator and look at moving to for example risk-based approaches. A good example of this would be adopting Risk-Based Inspection (RBI) for vessel inspections instead of e.g. 4-yearly internal vessel inspections.

       

      Failure Finding Maintenance (FFM)

      Failure Finding Maintenance tasks are aimed at detecting hidden failures typically associated with protective functions. Think pressure safety valves, trip transmitters and the like.

      This type of equipment won’t be required to function until something else has failed. That means that under normal operating conditions you will not know whether this equipment is still functional i.e. the failure modes are hidden.

      And since these failures are hidden, you’ll need to find them before you are relying on that equipment to protect you.

      Simple really.

      It’s important to realise that failure finding maintenance tasks do not prevent failure but simply detect it. And once detected you’ll have to repair the failure you found. Failure Finding Maintenance is conducted at fixed time intervals typically derived from legislation or risk based approaches.

       

      Risk Based Maintenance (RBM)

      Risk Based Maintenance (RBM) is when you use a risk assessment methodology to assign your scarce maintenance resources to those assets that carry the most risk in case of a failure (remembering that risk = likelihood x consequence).

      As a result, equipment that has a higher risk and a very high conseauence of failure would be subject to more frequent maintenance and inspection. Low risk equipment may be maintained at a much lower frequency and possibly with a much smaller scope of work.

      When you implement a Risk Based Maintenance process effectively you should have reduced the total risk of failure across your plant in the most economical way.

      Risk-Based Maintenance is essentially preventive maintenance where the frequency and scope of the maintenance activities is continuously optimised based on the findings from testing or inspection and a thorough risk assessment. Examples of Risk-Based Maintenance would be Risk-Based Inspection as applied to static equipment like vessels and piping or even pressure relief valves.

       

      Condition Based Maintenance (CBM)

      Most failure modes are not age related. However, most failure modes do give some sort of warning that they are in the process of occurring or are about to occur.

      If evidence can be found that something is in the early stages of failure, it may be possible to take action to prevent it from failing completely and/or to avoid the consequences of failure. Condition Based Maintenance as a strategy therefore looks for physical evidence that a failure is occurring or is about to occur. Thinking of CBM in this way shows its broader applications outside condition monitoring techniques often only associated with rotating equipment.

      An important concept within Condition Based Maintenance is the P-F curve shown in the figure below:

       

      pf curve for condition based maintenance

       

      The curve shows that as a failure starts manifesting, the equipment deteriorates to the point at which it can possibly be detected (point “P”).

      If the failure is not detected and mitigated, it continues until a functional failure occurs (point “F”). The time range between P and F, commonly called the P-F interval, is the window of opportunity during which an inspection can possibly detect the imminent failure and give you time to address it.

      It is important to realise that CBM as a maintenance strategy does not reduce the likelihood of a failure occurring through life-renewal, but instead is aimed at intervening before the failure occurs, on the premise that this is more economical and should have less of an impact on availability.

      In other words: condition monitoring does not fix machines and condition monitoring does not stop failures. Condition monitoring only lets you find problems before they become a failure.

      A common rule of thumb is that the interval between CBM tasks should be one-half or one-third of the P-F interval.

      How much more effective CBM is above breakdown maintenance depends on how long the P-F interval is. With plenty of warning the rectification can be planned, materials and resources can be mobilised and breakdown prevented (though production is still stopped for the maintenance duration). When the P-F interval is only a few days the resulting organisational and workplace actions are much like a breakdown and the value of CBM is largely lost.

      For CBM to be effective as a strategy, early intervention is essential. This requires an efficient and effective process for data gathering, data analysis, decision making and finally intervention.

      For failure modes where the P-F interval shows a large variability, condition monitoring is not an effective strategy.

      If you're interested to find more about how to best manage failure modes don't forget to check out my article Reliability Centered Maintenance - 9 Principles of Modern Maintenance.

      types of maintenance pdf

         

        Predictive Maintenance (PDM)

        Up until recently when people spoke about Predictive Maintenance (PDM) this was essentially as a synonym for Condition Based Maintenance. But in my view with the advent of Artificial Intelligence, much lower costs of equipment sensors (IIoT) and machine learning there is clearly a difference appearing between Predictive Maintenance (PDM) and Condition Based Maintenance (CBM), at least in my view.

        I see Predictive Maintenance as an extension, a more advanced approach to CBM where we use potentially many process parameters gained from online sensors to determine if our equipment is moving away from stable operating conditions and is heading towards failure.

        There are a lot of (very large) companies actively moving into this space and it is certainly a fast-moving and exciting part of our discipline as Maintenance & Reliability professionals. However, I do still believe that even the most advanced Predictive Maintenance approaches need to be underpinned by sound reliability principles and understanding.

         

        Corrective Maintenance (CM)

        A Run to Failure or Corrective Maintenance strategy only restores the function of an item after it has been allowed to fail. It is based on the assumption that the failure is acceptable (i.e. no significant impact on safety or the environment) and preventing failure is either not economical or not possible.

        Apart from being the outcome of a deliberate Run to Failure strategy Corrective Maintenance is also the result of unplanned failures which were not avoided through preventive maintenance.

        A run to failure strategy can effectively be used for general area lighting, smart process instrumentation (without trip functionality) etc. where the consequence of failure is limited and would not necessitate a need for an urgent repair.
        When opting for corrective maintenance as a strategy it is essential to ensure that the failure modes under consideration do not have the potential to become Emergency Maintenance. You see, if you adopt run-to-failure for equipment that once it has failed must be restored immediately to have doomed your organisation to a reactive maintenance environment. A reactive maintenance environment is not where you want to be. It is more expensive, less efficient, and less safe.

        So although a run-to-failure strategy can be a good option, make sure you decide wisely.

         

        Deferred Corrective Maintenance

        In the chart of maintenance types I broke ‘corrective maintenance’ into two sub-types:

        And that was very deliberate because it is so essential that we absolutely minimize the amount of Emergency Maintenance we allow into our organisations. As I already pointed out above Emergency Maintenance is expensive, various sources have suggested that Emergency Maintenance is 3 to 5 times as expensive as ‘normal’ preventive maintenance. Emergency Maintenance typically leads to longer equipment outages and more production impact. And it is less safe. So when a corrective maintenance work request is raised it is essential that you prioritise it properly to make sure that where possible you defer the work request and give your team the time to properly plan and schedule the work.

        If you want to read more about prioritisation of corrective maintenance have a look at the article You Will Fail Without Planning & Scheduling.

         

        Emergency Maintenance (EM)

        Emergency Maintenance is corrective maintenance that is so urgent that it breaks into your Frozen Weekly Schedule (you do have one don’t you?).

        It upsets your plans and schedules and typically throws everything into disarray.

        Some people thrive in this type of environment and often get heralded as heroes when they’ve worked 16hrs non-stop to get production back online. But when it comes to the Road to Reliability it is a dead end.

        So Emergency Maintenance is the one and only maintenance type that we really want to avoid as much as possible. In fact, World Class organisations ensure that less than 2% of their total maintenance is Emergency Maintenance.

        How much Emergency Maintenance do you have?

         

        Types of Maintenance: A Comparison Chart

        The Table below shows a brief summary of:

        • the different types of maintenance;
        • what type of tasks are involved;
        • the objective of the task;
        • and how the interval between the tasks is determined.

        An efficient and effective Preventive Maintenance Program will have a mix of all these different types of maintenance.

         

        types of maintenance

         

        Which type of maintenance is most expensive?

        The most expensive type of maintenance is Emergency Maintenance because this is the type of maintenance that is so urgent that you drop everything to run off and fix the problem. That means that Emergency Maintenance is usually not well planned (prepared) and therefore is highly inefficiency and expensive (typically at least 3 - 5 times as expensive as well planned preventive maintenance).

        Types of Maintenance PDF

        If you've found this article helpful and would like to get your own PDF copy of the article and a supporting presentation that explains the different types of maintenance and when to use them simply click on the link below and leave your details:

        types of maintenance pdf

          So what is breakdown maintenance?

          And frequently asked question is ‘what is breakdown maintenance’ and as it’s not in my explanation I thought I’d just covered it here briefly. As far as I am concerned, breakdown maintenance is simply corrective maintenance and not another type of maintenance in itself. In the case of breakdown maintenance you’ve had a failure and so now it needs to be fixed. And depending on the risk associated with that breakdown it could be urgent or less urgent.

          But, in many people’s mind, breakdown maintenance is urgent maintenance, maintenance that needs to be done right now i.e. Emergency Maintenance. And if that’s the case for you, you know what to do: get rid of it!

           

          What is the difference between preventive maintenance and predictive maintenance?

          I think I have covered this in the article, but as it’s such a frequently asked question I’ll just summarise the key differences here:

          • Preventive maintenance covers multiple types of maintenance that are used before a failure has occurred. Predictive maintenance is a form of preventive maintenance.
          • When most people talk about preventive maintenance they really mean Time Based Maintenance which is a repair or replacement on a fixed interval irrespective of the condition of the equipment. The interval can be time-based (days, weeks or months) or usage-based (operating hours, cycles or km).

           

          Are Planned Maintenance and Preventive Maintenance the Same?

          In my view, they are not the same. Planning refers back to the maintenance planning & scheduling process so planning maintenance is about preparing the maintenance work so that is ready to execute. whereas preventive maintenance is maintenance that has been identified to prevent or mitigate a failure mode.

          So in my view, Planned Maintenance is maintenance that has been through the planning process and is properly prepared with all job steps, labour, parts, and tools identified and organised.

          All Preventive Maintenance should be Planned Maintenance as it has been identified upfront and there is no reason why it would not go through the normal maintenance planning & scheduling process.

          The opposite of Planned Maintenance is Unplanned Maintenance which has not properly been prepared and is planned on the plan as the job is done. This is highly inefficient and something you should avoid at all cost. The only time you should be conducting unplanned maintenance is when you have a high priority work request that comes in and is so urgent that you break into the Frozen Weekly Schedule to complete the work without going through the normal planning & scheduling process. I refer to this as Emergency Maintenance.

           

          And what about Autonomous Maintenance?

          The above table of types of maintenance does not include Autonomous Maintenance or Autonomous Care (also referred to as Front Line Maintenance in other organisations). The CLAIR (Clean, Lubricate, Adjust, Inspect and Repair) activities conducted under Autonomous Care are essentially a combination of the above strategies, but conducted on a higher frequency by frontline staff.

           

          Which type of maintenance is most expensive?

          This an interesting question and generally speaking unplanned corrective maintenance i.e. Emergency Maintenance is the most expensive to conduct. This is because this type of maintenance does not go through the full maintenance planning & scheduling process because it's so urgent and it's simply planned on the fly. That means when you execute Emergency Maintenance you typically have very low efficiency with additional time wasted looking for materials, organising access to the equipment, waiting on other trades etc. Another common issue with Emergency Maintenance is that often parts and services are expedited to arrive faster and increased costs are incurred to make that happen.

           

          Why is Preventive Maintenance better than Breakdown Maintenance?

          In general, prevention of a failure is simply a lot cheaper and safer than letting equipment fail.  Plus, preventive maintenance would have much less impact on production than breakdown maintenance (i.e. running to failure).

          However, there are instances that a deliberate run-to-failure maintenance strategy is the right thing to do. A good example would be something like general area lighting in an industrial plant where you will simply wait till you have a number of lights that have ailed and then you replace them. Trying to replace these lights before they fail would be a waste of money because we cannot accurately predict when lightbulbs will fail. And because the consequence is low we can simply accept that general lighting is run to failure.

           

          Which is better, Preventive Maintenance or Predictive Maintenance?

          Predictive Maintenance really is a type of Preventive Maintenance as they both see you conducting maintenance before the failure has occurred. The issue is though that most people think of the traditional Time-Based Maintenance when they talk about Preventive Maintenance.

          So from that perspective which is better? Neither. You need to select the right maintenance type based on the failure mode you're trying to manage and its characteristics.

          If you have a failure mode that is random in nature you would want to opt for a condition-based or predictive maintenance task so that you can see the potential failure coming closer and take action before the failure occurs.

          But, if you have a failure mode that is very clearly age-related or where a condition based task is simply not economical then you would use a time-based maintenance task.

          Lube oil change out on a turbine with thousands of litres of oil is often best done on condition to ensure you get maximum life out of the oil. But, if you are only dealing with 50 liters of oil the time and effort it takes to sample the oil and analyse it probably means it's not worth going condition-based and you simply change that oil out based on a fixed time or fixed number of running hours.

           

          What Types of Maintenance Do You Use?

          Leave a comment below telling us what types of maintenance you use and why. Have you had great results with one specific type of maintenance let us know:

          66 Comments

          1. Commentators Gravatar  Anicete Pedro Gimbi on 12th Jul, 2018 at 9:28 PM

            Every time we use the preventive maintenance of drilling material and equipement to be really used and avoiid the corrosion .
            The process give us a good facility in offshore drilling over plateforms

            Sincerly

            Anicete

            • Commentators Gravatar  Erik Hupjé on 13th Jul, 2018 at 4:26 PM

              Thanks for the comment, indeed many corrosion mechanisms are time / duty related and can be effectively managed with a time based preventive maintenance regime. However, be careful with other random corrosion mechanisms like stress corrosion cracking which is not age-related and really needs to be designed out or managed through methods than time based PM.

          2. Commentators Gravatar  Rizaldi on 25th Jul, 2018 at 2:15 PM

            Hii,Sir,good definition about maintenance,
            i want to ask
            1.How many of percantage preventive maintenance,predictive ,and corrective standart world class.
            2.If we do activities of predictive,preventive and corrective,its call wrench time.
            Many thanks Sir.

            • Commentators Gravatar  Erik Hupjé on 25th Jul, 2018 at 8:41 PM

              Hi Rizaldi, I don’t like to give percentages for PM, CBM and CM ratios as people just take those numbers and forget to think. Instead I always like to point out that non-age related failure modes are typically > 70% of the failure modes we need to manage. And non age related failure modes are best managed with some kind of condition assessment so that gives you some indication. But also remember that often we have to do preventive maintenance to meet compliance / legislative requirements.

              Wrench time is basically the time your technicians are doing actual maintenance tasks so that excludes travel time, waiting time, time spent looking for parts and materials, time spent waiting for permits, time spent on breaks or meetings etc. Have a look at this article: https://roadtoreliability.com/sell-planning-scheduling/

          3. Commentators Gravatar  Tom on 26th Jul, 2018 at 12:40 PM

            Hi Erik,

            Inspections, vibration rounds, lubrication rounds, … are clearly preventive maintenance, but what if the preventive maintenance (e.g. a vibration reading, corrosion under insulation, …) found a possible error (upcoming bearing damage, a corrosion mechanism that cab lead to failure, …), does the repair or bring back in original state still fall under preventive maintenance or better to say proactive maintenance?

            Would you allocate all the costs to preventive maintenance or would you only allocate the cost for the initial inspection to preventive/proactive maintenance and allocate the repair/bring back to original state to corrective/reactive maintenance? I would prefer the former as the equipment did not fail yet.

            Thanks.

            • Commentators Gravatar  Erik Hupjé on 28th Jul, 2018 at 8:44 AM

              Hi Tom, If during a PM you find a defect that will eventually lead to a failure then I would consider correcting that defect still a PM as you are still preventing the failure from occurring. I like to keep things simple and therefore prefer a simple differentiation of it’s either a PM (before failure) or a CM (after failure). So all work and costs associated with preventing failures are PM costs.

              What you can do in some CMMS systems is to put a flag on the new work and mark it as follow-on work from a PM. That can help you determine how effective your PM is in finding issues.

              PS I’m not a big fan of the phrase proactive maintenance as it seems quite meaningless to me. All you PM’s are proactive in my view and where you have accepted a run to failure strategy I would even consider the resulting CM’s proactive as you have made a deliberate choice to allow that failure to happen (i.e. you have been proactive). I prefer to use the distinction of reactive vs proactive more around the overall maintenance culture rather than maintenance tasks. At that level i.e. a proactive or reactive maintenance culture makes sense to me.

              • Commentators Gravatar  Eddi Hakki on 2nd Oct, 2018 at 3:18 PM

                All take data from equipment and equipment not stop, it call Predictive Maintenance/Condition Based Maintenance.And then using data, make trending. From trending you could predict.

                If any found error during take data or from data reading, then make work orders, it call good corrective maintenance

          4. Commentators Gravatar  DHarmendra Mishra on 4th Aug, 2018 at 8:15 PM

            hi Erik

            what a great work you had done, thanks & keep it up

          5. Commentators Gravatar  Mgonja on 17th Aug, 2018 at 5:03 AM

            Great “digestion” on the maintenace field

            Well done Erik

            Thanks,

            Mgonja

          6. Commentators Gravatar  Viktor Laitinen on 28th Aug, 2018 at 7:04 PM

            Hi Erik,
            Thanks for your article.
            Unfortunately people are very conservative. Refusal of TIME BASED MAINTENANCE (TBM) them seems like a utopia.
            The lowest level is afraid of losing the job, Middle-level managers do not want to take responsibility for themselves, and senior management has an understanding of maintenance at the car care level.
            Sometimes it seems to me that we are banging our heads against the wall …
            BR
            Viktor

          7. Commentators Gravatar  Narender Kumar on 11th Sep, 2018 at 7:23 PM

            Hi Erik
            Thanks for the detailed description of maintenance. It was very informative.
            I have a different view on this. In my opinion, Maintenance are of only 2 types namely – Planned & Unplanned. These are the 2 types which I am concerned about. Target is to achieve more of planned maintenance. We do all predictive, fault finding to avoid Unplanned maintenance. That is when we achieve reliability. I do not like talking in terms of PM, CM, PdM etc as it makes the picture blurred. To get further details on the picture I like to have split for Planned i.e. CBM, PdM & PM. It gives me a clear picture whether we are doing PM or PdM more.
            I am not saying anybody else is doing it in a wrong way. It is just my way of doing things.
            In the end, the result matters

            • Commentators Gravatar  Erik Hupjé on 11th Oct, 2018 at 8:04 PM

              Hi Narender, I think we are actually very aligned in that your planned maintenance is the equivalent of my preventive maintenance and your unplanned maintenance is what I would call corrective maintenance.

              I prefer to keep the planned and unplanned distinction for (corrective) maintenance to identify those maintenance tasks that have not been planned i.e. prepared beforehand and therefore are typically very urgent, inefficient and a costly way to do maintenance. This is what I call emergency maintenance. And then you have planned (i.e. prepared) corrective maintenance where we have had a failure, but still are taking the time to plan the work so we get good efficiency.

              Preventive maintenance should always be planned (i.e. prepared)

          8. Commentators Gravatar  Ivan Robet on 9th Oct, 2018 at 6:06 PM

            I fully agree with what you state here. I am regularly delivering courses on railway maintenance, and i found myself so often faced with misunderstandings on basic concepts (even within professionals) that i developped a module of very basic maintenance concepts.
            Doing so i also discovered, even if this is odd, that those concepts are not always properly defined in academic books, and even in some standards.

            I may have 2 complements though.

            First is about Corrective vs preventive mn.
            As you say, they correspond to a decision, a strategy adopted, or as some books state, an evolution to “reactive” to “proactive”. The original poor or unknowledgeable maintainer would find himself in the reactive one, enduring failures that need to be repaired.
            But it could be misleading in terms of classification of tasks. They do not represent a mathematical “partition” of all the maintenance tasks. If one wanted to list out all maintenance tasks for a particular equipment, he would not be able to put 2 different lists. Because they do overlap.
            This is to me a reason of many confusions in non specialist minds.
            Some same tasks could be performed under corrective or preventive modes. For example greasing a door latch could be performed either once a door ceased to function (one cannot or cannot with sufficient ease slam it), i.e. in corrective mode, or when the door function is ok, or start to be less easy to slam (goes beyond the “p” point of the p-f curve), i.e. in preventive mode. Exact same task. Another example would be the replacement of a car wheel, that can be performed on a flat (failed) tyre or before the tyre gets too worn. Still exact same task, same series of steps.
            Many tasks can be performed exactly the same way, but just under different circumstances. This is also true that in some cases the tasks will somewhat differ, because when a failure occur some additional damages could have happened leadind to the necessity to accomplish other tasks when doing a repair. But not always.
            This seems to be just a small detail, but it is enough to create a confusion in terms of classification and logic for those who would think that preventive and corrective would represent 2 distinct categories of the maintenance tasks listed in a manual (Unfortunately many manuals do this mistake or this simplification).

            Second is about Surveillance / monitoring tasks
            Should a clear-cut split be made among all maintenance tasks, there would be 2 that are really distinct. There are on one hand those tasks dedicated on restoring function (greasing the door, changing the wheel), the interventions, and on the other hand those other tasks dedicated to assessing the state or condition of the equipment. Involving different skills, different tools, different process.
            Could be a measurement (size, current level, vibration level, reaction speed, aspect, sound, smell, etc) or some functional check leading to a conclusion regarding the equipment condition or level of performance regarding a function. It does not necessarily involves the use of a specific device, could be a simple glance to the wheel wear level, or a manual test of the latch resistance. It is where observation and experience comes into place in order to perform intervention only when appropriate. It involves other skills. When not performed, the intervention is done “blindly”. This is the glance to the shoe leading to the potential decision to polish it. Takes many glances before a polish is performed, usually ! They are usually simple, less expensive than interventions. It is what you do when you are lazy in your personal life, or “want to optimize” maintenance in your professional life. These tasks could be called “monitoring” tasks. Probably a better term could be used, i personally prefer the term “surveillance”. “Monitoring” often has the connotation of something made continuously (which is not necessarily the case here), and also can give the impression there will be some physical monitor (screen) involved, which is not the case either. As opposed to intervention where something is “made” to the equipment to restore its function, here nothing is made but the condition regarding a function is checked or assessed. It can be continuous or not, can involve a tool/ device or not.
            Condition monitoring maintenance, simply put, is this maintenance mode where some surveillance is preliminarily performed, with or without device, prior to intervention. This tends to optimize maintenance because it is based on solid and knowledgeable observation of a condition, and interventions which are usually expensive tend to be minimized. Surveillance activities are usually less expensive and shorter to perform, then less expensive.
            It could be said that performing preventative imposes to perform surveillance or monitoring tasks. Otherwise there are no garanty to remain preventive. This is why the “time-based” maintenance is weak. Involves no surveillance. This is a blind type of maintenance where interventions are performed disregardefully of equipment condition.
            This distinction is important for understanding, and it has the advantage of being “logical”.
            Unfortunately books rarely specify this distinction, which leads to mixing oranges and apples under the same general term of “maintenance tasks”, which not enough precise to correctly describe the other maintenance concepts within preventive maintenance. To me this distinction is key for understanding, and clearly missing in the maintenance litterature.
            Hope this will help complement your nice work !

            Best,
            Ivan Robet

            • Commentators Gravatar  Erik Hupjé on 9th Oct, 2018 at 9:37 PM

              Thank you Ivan for your detailed reply. Great point that the same task could be deemed preventive or corrective depending on when the task is done i.e. before or after failure.

          9. Commentators Gravatar  Debo on 25th Oct, 2018 at 1:24 AM

            Hi Erik,

            Thank you for the interested topic.
            I have confused about preventive maintenance and which better: renewal or replacement of complex assets.

            • Commentators Gravatar  Erik Hupjé on 25th Oct, 2018 at 8:52 AM

              Hi Debo, thanks for your comment. Whether you should replace or repair/overhaul a complex asset would depend on factors like the cost of repair ve cost of replacement and whether you expect to get the same reliability and life out of a repaired asset vs a new asset. Don’t forget that for a complex asset the overall failure pattern would most likely be random (see my article on the principles of modern maintenance) in which case time-based repair or renewal would not be an effective strategy.

          10. Commentators Gravatar  Rizaldi on 25th Oct, 2018 at 11:54 AM

            Good share Erick,at our site we clasify type of maintenance Proactive (PM,Pdm,Sca)maintenance and Reactive maintenance(emergency),PM we implement based on ,by time base equipment recomended,Pdm we implement by critical equipment mapping,Sca we implement by Work request and inspection.

          11. Commentators Gravatar  Wirza on 25th Oct, 2018 at 2:53 PM

            Hi Erik,

            It is really good reading. In our site (food & beverage company), we use PM (Preventive Maintenance), CM (Corrective Maintenance), and BD (Breakdown Maintenance).
            1. PM
            We have certain schedule for each equipment. Starting from weekly, monthly, 3 monthly, 6 monthly, yearly, 2 year, and so on.
            2. CM
            We conclude that when we do PM, we do CILT (Clean Inspect, Lubricate, Tightening). Some occasions when we found wear parts (the machine is still okay to run). But we don’t have spares in our store. So we need to order it to supplier and wait for part arrival. When the parts comes to our site, and when we do the replacement we call it by Corrective Maintenance.
            3. BD
            This type of maintenance conducted only if the machine stop in the middle of production. The cause will vary from wrong operational, equipment failure, and many more. Because it easier to note number of breakdown in one week, we use this for our maintenance priority.

            Please share what do you think

            BR

            • Commentators Gravatar  Erik Hupjé on 29th Nov, 2018 at 1:53 PM

              Hi Wirza, that aligns quite well with what I describe. We all have different ways and that’s totally fine. I think that putting a focus on breakdown maintenance (what I tend to call emergency maintenance) is really good as it helps to get out of the reactive environment

          12. Commentators Gravatar  Asim Eltom on 14th Jan, 2019 at 6:45 AM

            Hi Erik,
            Thanks for sharing this informative and clear work. The subject is very interesting. The good point you mentioned it. We have to think about principles, With this platform and the main classification is it before or after. My point for further discussion what about design out maintenance as way to improve capacity or reduce maintenance and other point opportunity maintenance.

          13. Commentators Gravatar  Mohammad Fadel on 6th Mar, 2019 at 1:04 PM

            Thanks Engr.Erik,
            It’s so useful information ,
            We apply preventive maintenance by 80% of our maintenance job
            The productivity is always high .

          14. Commentators Gravatar  Rashid on 21st Mar, 2019 at 4:28 AM

            Hi Erik

            Thanks a lot for useful and very interesting subject about type of maintenance. The following equations required specific and detailed answer

            1- Can u explain reliability vs PM
            2- How we can reduce CMs work order
            3- Long lead delivery spare part vs CM

          15. Commentators Gravatar  Enrique Báez on 22nd May, 2019 at 9:46 AM

            Excellent summary.. I had implemented in several organizations Plant Maintenance models and support them with Work Management tools. I had faced many times discussions with Maintenance heads on which is their maintenance strategy, and it is very frustrating that we have to start from basics and jump into a maintenance strategy or philosophy to respond to the business or equipment requirements.

            • Commentators Gravatar  Erik Hupjé on 22nd May, 2019 at 3:38 PM

              Thank you Enrique

              • Commentators Gravatar  Eyadeh on 23rd May, 2019 at 12:37 PM

                Hi Erik,
                Appreciate your great explanation about this topic, actually I am a student in maintenance engineering master program and I am about to start doing my research in some thing related to topic, but I want you to help me in choosing a maintenance topic for my research, it would be great if it was in aviation maintenance, any other topics also good.
                Thank you

                • Commentators Gravatar  Erik Hupjé on 23rd May, 2019 at 12:44 PM

                  Thank you for the comment Eyadeh. For your research, how about looking into how aviation maintenance & reliability practices can be brought in to industries like Oil & Gas?

                  • Commentators Gravatar  Eyadeh on 31st May, 2019 at 1:18 AM

                    Nice Erik, thank you so much, but can you please suggest more topics for my research, I really appreciate your help.



          16. Commentators Gravatar  Jacob Enco on 23rd May, 2019 at 2:37 PM

            Thanks for clarifying the types of maintenance tasks. I have been dealing with a system where they only classify into regular maintenance, non-critical issues and then critical issues. But obviously, and as you have explained, I suspected the maintenance tasks are more complicated than this. It’s not really in the scope of my current project exactly but after reading your breakdown I wonder if a more elaborate system of recording and dealing with the different maintenance tasks would help efficiency of maintainers. All the preventative tasks have been grouped together and cannot be distinguished to see where the problem is…

            • Commentators Gravatar  Erik Hupjé on 23rd May, 2019 at 2:44 PM

              Hi Jacob, thank you for your comment. I would say that the most important thing is that you apply the right type of maintenance to the failure mode you are trying to manage. How you classify your maintenance in your CMMS can help but I would not make this a priority until a lot of other things were in place.

          17. Commentators Gravatar  Sanjeev Duggal on 12th Jun, 2019 at 1:57 AM

            Hi Erik,
            Greetings!
            Types of maintencae is well explained by you. Very knowledgeable article.
            Regards

          18. Commentators Gravatar  Obeng Boampong on 12th Jul, 2019 at 6:17 AM

            Hello, please I want to know the various maintenance aids

            • Commentators Gravatar  Erik Hupjé on 12th Jul, 2019 at 7:21 AM

              Can you explain a bit more what you mean with various maintenance aids?

          19. Commentators Gravatar  Elisha k. juris on 13th Jul, 2019 at 4:30 PM

            Well done job sir!

          20. Commentators Gravatar  ghassan on 19th Sep, 2019 at 1:20 AM

            hello sir
            could you please send me the book, the research paper, or the reference of your writing about types of maintenance and selecting the best strategy, I need to read about it more, so that i can cite it in my research … regards

            • Commentators Gravatar  Erik Hupjé on 19th Sep, 2019 at 6:54 PM

              Hi ghassan, I wrote this based on my own industry experience, but there are actually a couple of international standards that cover this and where most of the industry terminology comes from.

          21. Commentators Gravatar  hazim on 26th Sep, 2019 at 10:54 PM

            Hi Erick
            my question is : what kind of maintenance can i implement for long off standing LV motors in oil and gas field to keep the resources
            thank you

            • Commentators Gravatar  Erik Hupjé on 29th Sep, 2019 at 6:51 AM

              Hi Hazim, try turning that question around: what failures may lead to those motors not being available when you need them? And then consider what tasks you could efficiently and cost-effectively do to mitigate the failure modes you identified.

          22. Commentators Gravatar  SYASYA on 9th Dec, 2019 at 5:40 AM

            Hai Sir,
            Can I know what is the suitable type and strategies of maintenance for heritage building?

            • Commentators Gravatar  Erik Hupjé on 27th Dec, 2019 at 7:22 AM

              The maintenance strategies and types you would use for building maintenance would depend on the failure modes you’re looking to manage, plus of course any legislative maintenance requirements. So for example you would use failure finding maintenance to test your building fire and smoke detectors on a regular basis. But you would probably use deferred corrective maintenance for any lighting maintenance, i.e. run lights to failure and then replace in a campaign once you have a number of lights fail. For an aircon system you would probably use time-based maintenance to replace filter elements.

          23. Commentators Gravatar  Abdulmagid sghair on 25th Dec, 2019 at 6:05 PM

            would please help me in suitable originations chart for oil company maintenance Section
            Regards
            A.Sghair

            • Commentators Gravatar  Erik Hupjé on 27th Dec, 2019 at 7:20 AM

              Do you mean ‘organizational chart’? If so, send me a more detailed message with a bit more background to your question via the contact page and I’ll do my best to answer.

          24. Commentators Gravatar  Ahmed Kassem on 23rd Jan, 2020 at 12:57 AM

            Hi Sir,

            I appreciate your great efforts and informative articles and I’m interested in reliability ( specially RCM ) and maintenance scheduling so I’m asking about the planning of preventive maintenance activities. ( By Reliability ( weibull) Vs Cost) or there is a better way!

            • Commentators Gravatar  Erik Hupjé on 23rd Jan, 2020 at 5:09 AM

              Hi Ahmed, thanks for your comment. When it comes to determining how often to do your preventive maintenance tasks comparing reliability vs costs can be a good approach, just be very careful with the data you use. Most organisations do not have the dataset to make these evaluations. That’s why I personally prefer a qualitative approach and then use a continuous improvement loop to enhance and optimise the PM program. Don’t forget to read my article on the principles of modern maintenance if you are interested in RCM.

          25. Commentators Gravatar  Ahmed Kassem on 23rd Jan, 2020 at 5:35 AM

            I will..Thanks a lot. and wish you success.

          26. Commentators Gravatar  Alex Kidd on 21st Feb, 2020 at 6:18 AM

            What a poor article!
            Typical maintenance theoretical statements.
            If we are not careful we will train all maintenance engineers of the future in these vintage theories.
            Obviously TBM has an important part to play in any maintenance strategy and this is getting pushed out by the penny pinchers.
            Any BUISINESS has to maintain product quality and operational effectiveness or it will never compete, therefore the operational running costs have to include a significant amount of Fixed TBM.

            • Commentators Gravatar  Erik Hupjé on 21st Feb, 2020 at 7:12 AM

              Thanks for your comment Alex. This article means to give an overview of the different maintenance types and in what circumstances they should be used. I agree that in many companies penny-pinching is a problem when it comes to maintenance, but I strongly believe that in those same companies maintenance teams do themselves a big disservice by executing a lot of non-value-adding maintenance tasks. And often these are time -based intrusive tasks that serve little to no purpose.

              • Commentators Gravatar  Bahrain Munir on 3rd Apr, 2020 at 4:05 PM

                Hi Erik, firstly thank you for this simplified theoretical maintenance strategy. Easy to read and make it easily understood.
                I’m fully agree with this discussion especially on this current Upstream O&G business situation where cost optimization (reduction?) and recent fallen oil price. For the next lines, please allow me to consider that the plant maintenance is part of safety matter due to the true goal is to preserve an asset from failure and decline (of course at the end to ensure business continuity). In the real life we have to asses all aspect that contribute to the business success provided with operational and safety excellence. Understood that safety margin is an imaginary line, therefore the operator is oblige to set the applicable and acceptable scope, context and criteria of the operation parameter considering either common best practices or domestic proven experiences. This would help the leader to make decision in selecting and prioritizing between business or safety. One famous approach is risk-based management decision.
                Since several years ago, we have been introduced with (Process Safety) Asset Integrity Management System on which maintenance management is one of its tools.
                Back to the current business/economical constrain. The operator must have depth understanding as well on the concept of deferred maintenance approach since its original/initial “positive” objective (e.g. cost optimization and minimal production interruption) could easily falling to the “unexpected” very costly compensation (e.g. long term high cost, equipment efficiency degradation, costly emergency intervention, major accident event, etc.).
                Just a cent from me.
                In this occasion please allow me to pray for the health of all of you wherever you are. May GOD protects us from this covid-19 outbreak.

          27. Commentators Gravatar  manish on 27th Feb, 2020 at 11:55 AM

            I have a query regarding ” what is Restorative maintenance in hardware and software”?

            • Commentators Gravatar  Erik Hupjé on 2nd Mar, 2020 at 5:18 PM

              I would suggest that restorative maintenance is to restore a function that has degraded which in my view would imply an age-related failure mode e.g. after so many hours of service a component is overhauled = restored. not sure how that would work with software though. Where did that phrase come from?

          28. Commentators Gravatar  Sanjeev Kumar on 12th Mar, 2020 at 10:40 PM

            Interesting read, some great points made and clear benefits to use of Preventive Maintenance although I believe it is more labour intensive with more frequent checks resulting in higher costs to run.

            I believe the solution to this is Predictive Maintenance in the form of simple wireless remote monitoring IoT network sensors that monitor your assets on a 24/7 basis that alerts you in real time to any abnormalities it detects preventing costly damages and maximising up-time.

            For further insight, feel free to read my article:
            https://www.chsservices.com/post/the-future-of-maintenance

            Thanks,

          29. Commentators Gravatar  AKSA on 14th Mar, 2020 at 8:44 PM

            Hi Erik,
            Can we say that predictive maintenance is a new type of maintenance appeared with industry 4.0 and not a branch of preventive maintenance?
            Thanks

            • Commentators Gravatar  Erik Hupjé on 15th Mar, 2020 at 7:42 AM

              I don’t think you can, fundamentally predictive maintenance is just like condition-based maintenance in that it aims to prevent or least mitigate the effect of a failure before the failure has occurred. As such it is a type of preventive maintenance.

          30. Commentators Gravatar  Lee Houghton on 12th Apr, 2020 at 1:48 PM

            What I have found with any form of maintenance, the names used on each site are based on what they consider the split, from an engineering perspective I find the following usually allow me to develop a full picture of the sites requirements
            1 Planned Preventative Maintenance (PPM) is used to monitor the items condition and functionality and make routine adjustments and corrections,
            2 Planned Corrective Maintenance (PCM) is used to restore degraded or compromised condition or functionality before it causes a failure, this can be asset condition from the previous PPM identified fault ie a camera dome getting degraded from UV being replace at the next PPM or a regular scheduled life expired type like replacing the batteries in an alarm system after 3 years of use.
            3 Life Cycle Upgrade (LCU) or Life of Type Upgrade (LTU) is the replacement of component parts at a set age to continue the systems functional level of service as whole, Usually this replace parts with a new more up to date version of parts that is no longer supported or manufactured without having to do a full upgrade.
            4 Reactive Corrective Reset (RCR), basically the resetting of the system after Operator Error or a system freeze or lockout. Well we have two components to this People and Computer/Mechanical, both cause issues that trip either designed safeties or move the system out of functional limits unintentionally.
            5 Unscheduled Corrective Maintenance (UCM) which is like PCM but the failure has occurred before either it has been identified and/or repair in time for a fault that should have been able to prevented from occurring.
            6 Reactive Corrective Maintenance (RCM) is any damage fault caused by unpredictable causes like a prisoner filling an intercom with toothpaste or lighting strike.
            7 Emergency Corrective Maintenance (ECM) covers any maintenance task from any of the methods of finding is of a mission critical nature or life preserving that just needs to be fixed right now. Includes call outs for stupid faults

            The last three are unfortunately the most common type of maintenance tasking that gets resourced even if spending the money on the first 4 actually saves a lot of the last 3 occurring in the first place. The trouble is most places never collect or at least use any information gained from performing the maintenance tasking to help improve/optimize the systems responses and cost impacts.

          31. Commentators Gravatar  Gavin Menzies on 15th May, 2020 at 12:49 AM

            It may be useful to refer back to Terminology: used n the context of Maintenance Contracts if not actually practised reference may be made to European Standard publication CEN 13306:2017 (E/F/D) “Maintenance: Maintenance Terminology” for clarification purposes.

          32. Commentators Gravatar  JIM VANTYGHEM on 30th May, 2020 at 1:22 AM

            Erik,

            You never cease to provide a wealth of knowledge. Your document is well presented, easy to understand, and useful for implementation.

            In our day and age of quick returns on investment, modeling the success of others who have proven strategies is an efficacious means of
            reaping the same rewards but in a much quicker time frame.

            I can not say enough great things about your contributions of time, effort, knowledge and experience given to the world of Reliability Engineering and Maintenance.

            For those who have not found the Road To Reliability community please do so. It will be worth your time.

          33. Commentators Gravatar  Hauzan Kamil on 25th Jun, 2020 at 10:59 AM

            This is a very basic knowledge and very important. So far, I use time-based-maintenance for almost all equipment under my responsibility. And I think I was wrong. Inadequate equipment maintenance will impact to safety also, maintenance members and others.
            Changing maintenance strategy is my next goal.

          34. Commentators Gravatar  Alok Shukla on 9th Jul, 2020 at 10:33 PM

            Hi Erik,

            I read your section it is very good and full of package.

            My question is that some time maker are recommend that after some time (every 20000 hours we have to change the oil ), but when we did our oil test analysis we found that oil is in good condition.

            So just suggest me we have to follow instruction of maker or we can run our equipment on the basis of our analysis. Oil changing work is too expensive.

            • Commentators Gravatar  Erik Hupjé on 10th Jul, 2020 at 7:17 AM

              Hi Alok, Thanks for the question. If you treat your lube oil well and analyse for the correct parameters then you can often extend the lube oil life well beyond the recommended change-out frequency recommended by the equipment manufacturer, but… you need to make sure you fully understand how the oil may degrade in your service, how you can detect degradation and how you will manage that (treatment or replacement). Replacing large lube oil quantities is indeed expensive but so is a significant equipment failure, so tread carefully. Depending on the quantities of oil involved and the potential replacement costs, it might be worth to hire an external specialist to help with this and develop a long term strategy.

          35. Commentators Gravatar  Moses Agaba on 17th Jul, 2020 at 6:03 PM

            Hi Erik, thanks for the good information. I have the following questions;
            1. What is the world class target for emergency maintenance ratio?
            2. What are the world class targets for MTBF and MTTR?
            Thanks

            • Commentators Gravatar  Erik Hupjé on 20th Jul, 2020 at 7:24 AM

              Hi Moses, world-class target for Emergency Maintenance would be <2%. I'm not aware of any world-class targets for MTBF or MTTR and they would not make much sense either as these metrics are very much equipment and location specific. Instead, I would suggest you look for reliability, availability or OEE benchmarks in your industry.

          36. Commentators Gravatar  Moses Agaba on 21st Jul, 2020 at 7:39 PM

            Thanks Erik for this clarification. I know the benchmark targets for availability and OEE, if I were to look at reliability, what measure and target would I look at?

            Thanks

            • Commentators Gravatar  Erik Hupjé on 22nd Jul, 2020 at 4:20 PM

              There quite a few ways to measures reliability as a performance metric, but I often recommend the use of uptime as a relatively simple metric that is easy to measure and understand. The desired uptime target would depend on equipment, industry and what drives value for your business.

          37. Commentators Gravatar  wen on 22nd Jul, 2020 at 6:06 AM

            Hi Erik
            Thanks for your article.

          38. Commentators Gravatar  Moses Agaba on 5th Aug, 2020 at 7:37 PM

            Hi Erik, most of key maintenance KPIs are lagging and most of them rotate on down time; which leading maintenance measures can I use and be able to control the outcomes of the maintenance process in a manufacturing industry?

            • Commentators Gravatar  Erik Hupjé on 5th Aug, 2020 at 9:10 PM

              Hi Moses, there are many KPIs or performance metrics that you can use to manage and improve maintenance. Quite a few will be lagging but there are plenty of leading indicators, it all depends on your goals and objectives. Some good leading indicators would be Schedule Compliance, Percent of Emergency Work, PM/CM Ratio, Wrenchtime, hours of training per year per maintenance technician, number of RCAs completed or Percentage of RCA Actions completed on time etc. etc.

          Leave a Comment