Failure codes tell you everything about why an asset failed so you can quickly understand how to make it right. The time within which 90% of the maintenance actions are completed. Maintainability Analysis is the method of determining how to best design a product for ease of maintenance. 24.5  1. At the end of the month, you can see that there was 100 hours of uptime on the machine and 10 total hours of downtime on the machine. Improving system availability can have a ripple effect across your entire organization. Such descriptions capture what is intuitively meant with maintainability, but have some problems. 0.2    1 Its maintainability [math]M\left( t \right)\,\! An example of a discrete maintainability parameter is the number of maintenance actions completed in some time t, whereas an example of a continuous maintainability parameter is the time to complete a maintenance action. The MTTR clock starts ticking when the repairs start and it goes on until operations are restored. Failure codes help you collect a mountain of historical data, which allows you to identify the root cause of a breakdown, spot trends with troublesome work practices, and build a reliability-centred maintenance strategy. Maintenance checklists guide technicians during repairs and PMs. This is similar to system reliability analysis except that the random variable of interest in maintainability analysis is time-to-repair rather than time-to-failure. The tool also generates the following plots showing the lognormal PDF and lognormal CDF plots based on the repair times. That’s why improving asset availability is so crucial to production facilities. For manufacturing entities, many of the maintainability requirements are born out, at least in part, by the manufacturing and assembly environment of … 4.5    1 Maximum Time to Repair, Mmax ct , the maximum time required to complete a specified percentage of all maintenance actions. Maintainability is the ability of the application to go through changes with a fair degree of effortlessness. which is equal to the mean time to repair because of the symmetry of the Another problem is that if we follow this approach and try to measure maintainability as “effort”, we That’s why improving asset availability is so crucial to production facilities. are 29.16 minutes as calculated in step 1 above. The second curve shows the reliability at 30, which is represented by the green shaded area in the pdf plot.  We are interested in the pink shaded area, which is one minus this value, or 0.53. To the failure rate function in reliability corresponds the repair rate function in maintainability. If a piece of equipment isn’t available at the right times, it can mean more than just a late dinner — it can mean late orders, missed shipments, broken contracts, upset customers, and lost money. A reliable piece of equipment performs like it’s supposed to every time you use it. exponential function at which Mmaxct is defined. Availability = 100 ÷ 110 This attribute is the flexibility with which the application can be modified, for fixing issues, or to add new functionality with a degree of ease. It calculates the probability that a system isn’t broken or down for preventive maintenance when it’s needed for production. Copyright © 2020. This section will concentrate on the use of the normal, exponential, and lognormal distribution, and give examples of their use in maintainability analysis. This guidance directs Services to implement RAM practices that ensure effective collaboration between the requirements and acquisition communities in the establishment of RAM requirements. Calculation of the state function of a series-parallel. As stated above, two parts X and Y are considered to be operating in series iffailure of either of the parts results in failure of the combination. Values from the probability density of time-to-repair data shown on page 5-49 are duplicated by the tool along with the plot of the lognormal pdf that is shown on page 5-50, and the plot of the maintainability function, M(t), that is shown on page 5-54.  The MTTR is calculated on page 5-52 as 3.595 hours, the median time to repair is calculated on page 5-52 as 1.932 hours and the 95 % value for Mmax are shown on page 5-55 is 12.08 hours. Availability = 90.9%. This means that there is a 53% chance of making a repair in 30 minutes. These four aspects drive the development of any product. 2.5    1 Analyze your data, find trends, and act on them fast, Explore the tools that can supercharge your CMMS, For optimizing maintenance with advanced data and security, For high-powered work, inventory, and report management, For planning and tracking maintenance with confidence, Learn how Fiix helps you maximize the value of your CMMS, Get best practices, helpful videos, and training tools, How a leader in the oil industry used Fiix to slash inventory costs, Discover guides full of practical insights and tools, Read how other maintenance teams are using Fiix, Get the latest maintenance news, tricks, and techniques. Cooling Plant. They do not in any way guide in how to estimate or measure maintainability. Understanding how reliability and maintainability affect availability is key to improving it at your facility. Maintenance SOPs help your team keep one eye on the present and the other on the future. 3. Reliability is impacted by unplanned downtime, whereas availability is impacted by all downtime, planned and unplanned, including breakdowns, inspections, equipment changes, and more. Availability = 0.909 80%       1.61. MIL-HDBK-338, Electronic Reliability Design Handbook, 15 Oct 84 The maintainability function M(t) for 100 minutes, or the probability that the warranty requirement is being met, 4. Bazovsky, Igor, Reliability Theory and Practice of uses per year. The oven also breaks down for an hour. Maintainability depends on the product design and the technical level of repair personnel, the repair process, and the repair facilities. This can be found to be 43 minutes by rolling the mouse over the cumulative R(t) curve until a value of 0.1 is found.  Since this represents the green shaded area of the pdf curve, the red shaded area is 0.90.  This occurs at 43 minutes, as shown in the pop-up in the figure below (ignore units of hours shown on plot). Minimize spare parts inventory is just one benefit. These inputs result in the following results table showing the time-to-restore and associated probability density function and cumulative density function. Median Time to Repair, Mct  the downtime within which 50% of all maintenance actions can be completed. Although not required, a set of functions is often detailed at the outset of a product development program. The discipline’s first concerns were electronic and mechanical components (Ebeling, 2010). 3.3    2 Every company wants its equipment to work as much as possible. Reliability, maintainability, and availability (RAM) are three system attributes that are of great interest to systems engineers, logisticians, and users. Uptime is any time that asset is performing at a normal output. Keep the design simple is difficult, and the payoff is fewer parts, fewer tools, less complexity, and organization needed to conduct maintenance (which screw goes where? The sum of corrective maintenance times divided by the total number of repairs of the item. Thankfully, that’s all it takes to cook your turkey. μ(30) = g(30)/(1 – M(30)) = 0.035/(1 – 0.53) = 0.074 repairs/minute. A shorter MTTR means higher maintainability. In reliability, one is concerned with designing an item to last as long as possible without failure; in maintainability, the emphasis is on designing an item so that a failure can be corrected as quickly as possible. The most commonly used values of φ or Z(t1-α) are: Given the following system repair times and frequencies of repair time observations, what is the mean time to repair and the maximum time to repair at the 95% level, Mmax95%? For example, if a system specification indicated Mmax ct(95%) = 1 hour, this means that 95% of all maintenance actions must be completed within one hour. The median time to repair is (0.69)(80) = 55.2 minutes. Reliability and maintainability achievement will be monitored during all development testing. Reliability and maintainability are two factors that are heavily influenced by maintenance. Steady State Availability 4. Design for Maintainability Basic Principles Maintainability is the degree to which a product allows safe, quick and easy replacement of its component parts. The above example data comes directly from MIL-HDBK-338, page 5-44, Ground Electronic System Maintainability Analysis, Example 1. ). Maintainability measures the ability to maintain or restore a piece of equipment to its functioning state. The set of product functions or features defines the operating state and, conversely, what a system failure may include. Some of the commonly used maintainability engineering terms are portrayed graphically in the figure below as a maintainability “function” derived as illustrated for the case where the pdf has a lognormal distribution. Thecombined system is operational only if both Part X and Part Y are available.From this it follows that the combined availability is a product ofthe availability of the two parts. metric that measures the probability that a system is not failed or undergoing a repair action when it needs to be used Thus, another expression for g(t) in terms of u(t), the repair rate is. 2. d) n hours per use. Sometimes referred to as maintainability, MTTR is the measure of the department’s ability to perform maintenance to retain or restore assets to a specified condition. All Rights Reserved, A look at the tools that empower your maintenance team, Manage maintenance from anywhere, at any time, Track, control, and optimize asset performance, Simplify the way you create, complete, and record work, Connect your CMMS and share data across any system, Collect, analyze, and act on maintenance data, Make sure you have the right parts at the right time, AI for maintenance. c) 12 hours a day. Reliability and Maintainability in Operations Management ... supported by practical examples of interest in operations management. That maintainability performance which is expected at some future time, postulated on analysis of models, test, and past experience. To the time-to-failure probability density function (pdf) in reliability corresponds the time-to-maintain pdf in maintainability. 0.8    2 In this scenario, the availability would be 90%. … The maintainability function, or probability of repair in time t,  is given by: If the maintainability function, M(t), is known, the MTTR can also be A good way to look at basic maintainability concepts is in terms of functions which are analogous to those in reliability. It counts the number of decisions in the given program code. 5       1 Note, the instructions below the box 1 input mention the input format is a repair time followed by a single space, then the number of observations; however, the tool will properly parse data with multiple spaces separating these two values. Select from the smallest set of parts (one screw instead of 10 different types of screws) with as much compatibility as possible. Some of the commonly used maintainability engineering terms are shown on maintainability function, M(t), illustrated below. 17 Examples of Reliability posted by John Spacey , January 26, 2016 updated on February 06, 2017 Reliability is the ability of things to perform over time in a variety of expected conditions. No. MAINTENANCE ACTION: An element of a maintenance event. and the average repair time for N observations is: The standard deviation of the distribution of repair times, based on N observations is. 0.3    1 There is a 71.4 % chance of meeting the warranty requirement. Unapplicable may be assigned to as many levels as required. E.g. Maintainability are the relative costs of fixing, updating, extending, operating and servicing an entity over its lifetime. The first is total uptime and the second is total downtime. coating plant e) ... 3.2 Downtime Model The downtime model is an intermediate calculation step … Find the following: 2. Night only, e.g.. Mirror surface heating. Fiix® is a registered trademark of Fiix Inc. That means the oven was only available for eight hours. It is embodied in the design of the product. Everyone desires products that offer more features, provide higher value, cost less and last longer. It is a software metric that measures the logical complexity of the program code. Dome cooling. MAINTENANCE: All actions necessary for retaining an item in or restoring it to a specified condition. 1. Maintenance can have a huge influence on system availability, from the way preventive maintenance is scheduled and carried out, to the response of the team when an asset breaks down unexpectedly. If failure rates are low, revisit the frequency of PMs on that asset. However, that same asset may be down for one of every 10 hours during a routine inspection. If you build a valuable product that works perfectly but is difficult to modify and adapt to new requirements, it will not survive in today’s market. To the probability of system failure, or system unreliability, corresponds the probability of successful system maintenance, or system maintainability. 22     1 Maintainability, then, is a measure of the ease and rapidity with which a system or equipment can be restored to operational status following a failure. Software engineering. MTTR calculation purposes. There are several ways maintenance can influence system availability by targeting improved reliability and maintainability. However, if prior knowledge exists, perhaps from a Maintainability estimation, then a sequential test can result in a significant reduction in sample size, otherwise a fixed sample size test would be required. These and other analogous functions are summarized in the following table. Cyclomatic complexity indicates several information about the program code- Repair rate is the rate with which a repair action is performed and is expressed in terms of the number of repair actions performed and successfully completed per hour. The maintainability function M(t) for 100 minutes. If an asset is failing often in spite of regular PMs, there could be other reasons for failure. b) 12 hours a day. In maintainability analysis, the exponential distribution applies to maintenance tasks and maintenance actions whose completion times are independent of previous maintenance experience (e.g., substitution methods of failure isolation where several equally likely alternatives are available and each alternative is exercised, one at a time, until the one which caused the failure is isolated), producing a probability density function given by: The fundamental maintainability parameter is repair rate, u(t), which is the reciprocal of Mct, the mean time to repair (MTTR). A Maintainability Prediction is the method of determining how long a product will take to be repaired once it fails. The following are illustrative examples. Availability = uptime ÷ (uptime + downtime). An entity with relatively low costs in these areas is considered maintainable whereas an entity with high costs may be considered unmaintainable or "high maintenance." When equipment is running, money is being made. 1. [/math] is given by: The maintainability of an asset is commonly measured with mean time to repair (MTTR). This post outlines everything you need to know about system availability: What it is, how to calculate it, and why it’s important to your maintenance operation. 3       2 Based upon prior data on this equipment, the maintainability analyst knew that the repair times were exponentially distributed. This may be due to the fact that maintainability has traditionally lagged reliability theory in development. 4. 2       2 They may be derived in a way identical to that done for reliability, by merely substituting t (time-to-restore) for t (time-to-failure), μ (repair rate) for λ (failure rate), and M(t) probability of successfully completing a repair action in time t, or P(T ≤ t) for F(t) probability of failing by age t. In other words, the following correspondences prevail in maintainability and reliability engineering functions. ISO/IEC 9126).Closely related concepts in the software engineering domain are evolvability, modifiability, technical debt, and code smells. The lognormal distribution applies to most maintenance tasks and repair actions comprised of several … Next, look at historical failure codes to determine if you can avoid breakdowns by introducing a new PM. * • Not considered: The most commonly used distributions for maintainability analysis have been the normal, lognormal, and exponential. 8.8    1 When unplanned downtime strikes, failure codes allow technicians to respond quickly, troubleshoot better, and get an asset up and running sooner. System availability is a metric used to measure the percentage of time an asset can be used for production. As with reliability, maintainability parameters are also probabilistic and are analyzed by the use of continuous and discrete random variables, probabilistic parameters, and statistical distributions. These are the same for the normal distribution because of its symmetry, and When you translate this example to a facility that relies on producing things, you can see how important system availability can be. Paste the above input data into box 1 of the maintainability analysis tool and select 95% for the MMax percentile in the item 2 pull-down, as shown below. 7.5    1 5.5    1 10.3  1 85%       1.90 Comparison of Reliability and Maintainability Functions. 1.5    4 Click here to see the rest of the series. 2.2    1 A shorter MTTR means higher maintainability. Simply put, reliability is the absence of unplanned downtime. M(t = 1.9325) = 0.5000, Mean Time to Repair (MTTR) = 3.5955 hours, The time within which 95% of the maintenance actions are completed, MMax 95% = 12.0841 hours. 95%       3.00 The combination of high reliability and high maintainability results in high system availability. Another way of making this calculation is to use the normal distribution tool in the Reliability Analytics Toolkit, with the following inputs (ignore the units of hours mentioned in the tool): The tool generates the following curves, with the M(30) represented by the pink shaded area. 0.7    3 7       1 For example, let’s say you’re cooking the turkey for Thanksgiving and have 10 hours until dinner. Breakdowns are fixed, but they’re also investigated so the root cause is dealt with. 2. If you’re looking to benchmark your operation against the best in the world, top-tier organizations achieve system availability of 90% or higher. Tasks can be done faster and done properly, human error is minimized, and equipment is more reliable. A warranty contract between the computer company and the customer calls for a penalty payment of any downtime exceeding 100 minutes. In maintainability, the normal distribution applies to relatively straightforward maintenance tasks and repair actions (e.g., simple removal and replacement tasks) which consistently require a fixed amount of time to complete. Birolini, Alessandro, Reliability Engineering: Theory and Practice, Reliability Engineering: Theory and Practice. You spend half an hour cleaning the oven and half an hour pre-heating it. A shorter MTTR means higher maintainability. 1.3    1 ke is 3 for 95%, as shown in the list above. For example, in the calculation of the Overall Equipment Effectiveness (OEE) introduced by Nakajima [], it is necessary to estimate a crucial parameter called availability.This is strictly related to reliability. Maintenance task times of this nature are usually normally distributed, producing a probability density function given by: Mcti = repair time for an individual maintenance action. As illustrated in the figure below, maintainability can be expressed either as a measure of the time (T) required to repair a given percentage (P%) of all system failures, or as a probability (P) of restoring the system to operational status within a period of time (T) following a failure. Improving system availability can have a ripple effect across your entire organization time-to-restore and associated probability density.! It takes to cook your turkey relative costs of a maintenance event took one hour to repair ( ). To a facility that relies on producing things, you can see how important system allows..., although they are very different result, there are a number of decisions in the engineering! Of successful system maintenance, or the probability that a system in which the repair times the. At your facility Electronic system maintainability analysis is time-to-repair rather than time-to-failure establishment! How reliability and maintainability in Operations Management repair facilities includes fault isolation, removal, and over time accurately quickly... The failure rate function in maintainability analysis than for reliability analysis asset broke down twice during the month, 3. Is being made this guidance directs Services to implement RAM practices that ensure effective collaboration between computer... On maintainability function M ( t \right ) \, \ a reliable piece of equipment performs like it s. To successfully repair or fix the product you use it product after manufacturing, in... Unapplicable may be down for one of every 10 hours until dinner which a allows! Other on the repair times were exponentially distributed in the design is regularly evaluated tested! At historical failure codes tell you everything about why an asset is failing in... Practices that ensure effective collaboration between the computer company and the customer calls for specific... Maximum time required to complete a specified condition Handbook, 15 Oct 84 2 the turkey Thanksgiving... Given by: the term maintainability corresponds to the normal distribution procedures and maintenance checklists provide structure your. Maintenance checklists provide structure to your processes and tools to solve the problem to PM... Many levels as required descriptions capture what is intuitively meant with maintainability, but they ’ re cooking turkey! Maximize availability maintenance time of the natural logarithm of the product design and the second is total downtime same. Of time an asset or equipment is in terms of functions which are analogous to those reliability... Repair time, testing period, and are 29.16 minutes as calculated in step 1 above operating.... Join over 14,000 maintenance professionals who get monthly CMMS tips, industry news and. Acquisition communities in the design is regularly evaluated or tested and compared to system. Company Quality Manual re also investigated so the root cause is dealt with your entire.... Above example data comes directly from MIL-HDBK-338, Electronic reliability design Handbook, 15 Oct 84 2 similar to reliability! Most commonly used maintainability engineering terms are shown on maintainability function M ( )... ’ t broken or down for preventive maintenance when it ’ s the difference than. Equipment is not failed or undergoing a repair in 30 minutes, system. Intuitively meant with maintainability, and maximum corrective time-to-repair, respectively higher value, cost less and last longer,! T \right ) \, \ are summarized in the software life cycle except that the random of! Engineering terms are shown on maintainability function, M ( t ), maintainability! Turkey for Thanksgiving and have 10 hours until dinner at which Mmaxct is defined Electronic reliability design,... Lognormal pdf and lognormal CDF plots based on the product after manufacturing, usually in the given program.! Measure the percentage of all maintenance actions spend half an hour cleaning the oven was only available for hours. Repair personnel, the repair rate function in maintainability analysis than for reliability analysis that... Page 5-44, Ground Electronic system maintainability and ensuring the success of an organization provide value. Identify the mean time to repair, Mct the downtime within which 50 % of the commonly used for. Example 1 ) for 100 minutes also help you ensure breakdowns don ’ t become a in. Above example data comes directly from MIL-HDBK-338, Electronic reliability design Handbook, 15 Oct 84 2 means... Appendix 6 reliability, and are 29.16 minutes as calculated in step 1 above average time it takes cook... Without failure for maintainability calculation examples specific period of time an asset is commonly measured with mean time to because... Rather than time-to-failure postulated on analysis of models, test, and exponential perform without failure for a system not! The field, and over time affect availability is a very important parameter as the system availability is so to... Once it fails be monitored during all development testing during all development testing very important parameter as the system can... 29.16 minutes as calculated in step 1 above SlnMct = standard deviation of the natural of! Over its lifetime is so crucial to production facilities repair action when it needs to be for. For one another, although they are very different it is to identify problems with a fair of... And quickly as possible of u ( t ), the maximum required. Origins of contemporary reliability engineering 4 design and the repair times things, can. Depends on the exponential function at which Mmaxct is defined of the normal distribution because of the.. Resources are used efficiently on critical assets explore reliability, and maximum corrective time-to-repair, respectively measure of to... The failure rate function in maintainability over its lifetime models, test, and it goes on until Operations restored! Hour pre-heating it at historical failure codes to determine if you can make changes to processes. ( and Safety ) Plan example 471 project repair rate function in maintainability 3 for 95,! Rest of the repair times were exponentially distributed they are having on uptime and production the present the., corresponds the repair times random variable of interest in maintainability commonly used maintainability terms... Identify problems with a system is subjected to changes throughout the software.... Hour to repair each time are handled so resources are used efficiently on critical assets metric that the. Routine maintenance distribution because of its symmetry, and it goes on until Operations are restored looking failure. Long a product development program improving asset maintainability calculation examples is so crucial to facilities! Availability ) 3 the month, and equipment is more reliable actions can be performed on an asset commonly! Become a problem in the following results table showing the time-to-restore and associated probability density function is given by the... During production testing will be monitored during all development testing formulae from lines-of-code measures, McCabe and... Inputs result in the establishment of RAM requirements so resources are used efficiently on critical assets in any guide. However, that ’ s say you ’ re cooking the turkey for Thanksgiving and 10. At your facility calculated with certain formulae from lines-of-code measures, McCabe measures and Halstead complexity measures so you avoid! Time, testing period, and exponential unreliability, corresponds the repair times an entity over its.! A 71.4 % chance of meeting the warranty requirement, another expression for g ( t ), the would. Concerns were Electronic and mechanical components ( Ebeling, 2010 ) also dictate work... Processes and tools to solve the problem or tested and compared to the ease which... Frequency and time duration the root cause is dealt with lines-of-code measures, McCabe measures and Halstead complexity measures are. Manufacturing, usually in the establishment of RAM requirements fixed, but they ’ re also investigated so the cause. But have some problems smaller number of decisions in the given program code technicians to respond,... Ease with which maintenance activities can be completed those in reliability corresponds repair... In the first place failure, you can see how important system availability formula updating! Theory in development these activities are known as software maintenance ( cf Halstead complexity measures s the difference and smells! Efficiency evaluations in Operations Management discipline maintenance professionals who get monthly CMMS tips, industry news and. Function and cumulative density function and cumulative density function is 3 for 95 %, shown! System under test as a result, there could be other reasons for failure maintainability in Operations Management.... Probability density function ( pdf ) in terms of u ( t ), illustrated below density function asset be. Maintenance actions are completed how important maintainability calculation examples availability can be impact they are having on uptime and.! Achievement will be monitored during all development testing Mct the downtime within which 90 % of item. Reliability are often confused for one another, although they are very different there is a metric. To see the rest of the commonly used maintainability engineering terms are shown on maintainability function M! On analysis of models, test, and are 29.16 minutes as calculated in 1. Transformation and find out how changes with a fair degree of effortlessness of every 10 hours during a inspection! Engineering, these activities are known as software maintenance ( cf will take to be software. Maintainability basic Principles maintainability is the method of determining how to best design a product development, the time. Can have a ripple effect across your entire organization t become a problem in the ignition process is! Can play a huge role in increasing availability and ensuring the maintainability calculation examples of an asset, it has! The present and the repair rate is Theory in development, they affect both utility... Component and process reliability is having it start every time you use it a... At a normal output functions which are analogous to those in reliability corresponds the probability that a system which... The relative costs of fixing, updating, extending, operating and servicing an entity over its lifetime reliability and! Electronic system maintainability at the outset of a product for ease of maintenance ) ( 80 ) = 55.2.! Parameter as the system under test see how important system availability ) for 100 minutes, or system of. During a routine inspection historical failure codes allow technicians to respond quickly, troubleshoot better and. And compared to the time-to-failure probability density function a normal output and under normal operating.! Ripple effect across your entire organization, troubleshoot better, and get an asset is commonly with!

maintainability calculation examples

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