The failure rate is a basic component of many more complex reliability calculations. Where: More often, systems contain parallel and serial subcomponents as depicted in Figure 11. More detailed understanding of field data collection. I encourage you to further investigate the field of reliability engineering methods, concentrating on the following topics, among others: More detailed understanding of the Weibull distribution and its applications, More detailed understanding of the exponential distribution and its applications, The Gaussian distribution and its applications, The log-normal distribution and its applications, Confidence intervals (binomial, chi-square/Poisson, etc. λ = Failure rate (1/MTBF, or 1/MTTF), In our electric motor example, the actual likelihood of failure at three years is calculated as follows: This is due to the combined influence of design engineering, procurement, production/operations, maintenance, etc., and the difficulty in creating effective tests and experiments to model the multidimensional aspects of a typical production environment. This is assessed by examining the coefficient of correlation R, or more conservatively, R2, which denotes data variability. BASIC QUALITY CONCEPTS . Depending upon the shape parameter, the Weibull failure density curve can assume several distributions, which is what makes it so versatile for reliability engineering. Conversely, if Weibull analysis revealed that the motors exhibited predominantly wearout-related failures, yielding a β shape parameter of 5.0, the estimate of reliability at six years time would be ~ 93%, instead of the ~55% estimated assuming the exponential distribution. When evaluating the reliability and failure characteristics of a machine, we must begin with the much-maligned “bathtub” curve, which reflects the failure rate vs. time (Figure 2). Reliability Engineering in the development process is the discipline of quantifying a product’s reliability requirements, while ensuring that practices are in place to design in reliability, and verifying that reliability requirements are met through design analysis and testing. For non-redundant items this is the equivalent to definition (1). Combination System with Parallel and Serial Elements. As such, the risk of failure is highest just following initial start-up. But once you understand the mechanics of the formulas, the math is really quite simple. Not a complicated tool to use, reliability block diagrams simply map a process from start to finish. Most important, spend time learning how to apply reliability engineering methods to plant reliability problems. To employ the reliability analysis methods described herein, the engineer requires data. Capability – A measure of the ability of an item to achieve mission objectives given the conditions during the mission. This graphic visually illustrates the concept of increasing risk vs. time (β = 0.5), constant risk vs. time (β = 1.0) and increasing risk vs. time (β = 5). Certified Reliability Belt Program the concept Reliability and lifetime of products and machines today are a central success factor with regard to marketing and competitors. Following the run-in period, we might introduce monitoring techniques that are targeted at the time-dependent wearout failures that are believed to affect the system, increase monitoring frequency accordingly or schedule “hard-time” preventive maintenance actions in some cases. The purpose for quantitative reliability measurements is to define the rate of failure relative to time and to model that failure rate in a mathematical distribution for the purpose of understanding the quantitative aspects of failure. The Probability Density Function (pdf). The cost and high-profile nature of aviation related accidents helped to motivate the aviation industry to participate heavily in the development of the reliability engineering discipline. Not dependent. Before discussing series systems, we should discuss reliability block diagrams. The simple parallel system in our example with two components in parallel, each having a reliability of 0.90, has a total system reliability of 1 – (0.1 X 0.1) = 0.99. The basic concepts of set theory and probability theory are explained first. λ = Failure rate (1/MTBF, or 1/MTTF), In our electric motor example, if you assume a constant failure rate the likelihood of running a motor for six years without a failure, or the projected reliability, is 55 percent. When these are lumped together, there is a “randomizing” effect, which makes the failures appear to lack any time dependency. More and more, these methods are being employed to assure the production reliability of manufacturing plants and equipment – often as an enabler to lean manufacturing. PRINCIPLES OF RELIABILITY ENGINEERING Training Duration 5 Days Training Date & Duration REF RM045 Principles of Reliability Engineering 5 5-9 Aug $5,000 Dubai, UAE Will be held at any of the 5 star hotels. The methods described herein are routinely used by reliability engineers and are core knowledge concepts for those pursuing professional certification by the American Society for Quality (ASQ) as a reliability engineer (CRE). Design and procurement is analogous to genetic predisposition; installation and commissioning is analogous to prenatal care and mother’s nutrition; and lifestyle choices and availability of medical care is analogous to maintenance effectiveness and proactive control over operating conditions. Incidentally, we would estimate MTBF for electric motors that are rebuilt upon failure. Below is the pdf for the exponential distribution. For convenience, a highly abridged list of key terms and definitions is provided in the appendix of this article. pdf(3) = .07408 = ~ 7.4%. k = The maximum allowable number of failures Armed with this knowledge, he or she is better positioned to take mitigating actions. θ = Mean time between/to failure However, as the population declines as a result of failure, the actual number of mathematically estimated failures decreases as a function of the declining population. Its scope is not limited to anyone engineering discipline as the concepts and basic techniques for reliability evaluation have no disciplinary boundaries and are applicable in most, if not all, engineering applications. Learn Reliability Engineering basics, application of analysis tools, reliability strategy development, and implementation of workplace improvements . Failure mode – The consequence of the mechanism through which the failure occurs, i.e. For example, if five electric motors operate for a collective total time of 50 years with five functional failures during the period, the failure rate is 0.1 failures per year. Where: In our pulverizer example, assuming a subcomponent reliability of 0.90, the equation works out as a summation of the following: However, if the failure modes were analyzed individually, the story would likely be very different (Figure 13). Once plotted, the linear slope of the resultant curve is an important variable, called the shape parameter, represented by â, which is used to adjust the exponential distribution to fit a wide number of failure distributions. r = The total number of failures occurring during the investigation period. If the shape parameter exceeds about 3.5, the data are time dependent and indicate wearout failures. Before discussing methods, you should familiarize yourself with reliability engineering nomenclature. Learn how we use cookies, how they work, and how to set your browser preferences by reading our. β = Weibull shape parameter from plot. Many data sets will exhibit two or even three distinct regions. during an investigation period for both failed and non-failed items. Simple r/n system example – Three of the four components are required. There are some shortcut methods for calculating parallel system reliability when all subsystems have the same estimated reliability. This course will introduce and familiarize you with the basic concepts and skills of estimation, prevention and management of product lifecycle … Where: Surprisingly, despite the versatility of the Gaussian distribution in modeling probabilities for phenomenon ranging from standardized test scores to the birth weights of babies, it is not the dominant distribution employed in reliability engineering. β = Weibull shape parameter from plot. However, engineers must be particularly clever in their application of the methods. Exact venue will be informed once finalized. ), Bayesian applications of reliability engineering methods, Testing options and their applicability to plant reliability engineering, Reliability growth strategies and management. The Gaussian distribution is generally applicable to data sets where the two most common measures of central tendency, mean and median, are approximately equal. Not independent. R1-n(t) – Subsystem or sub-function reliability for given time (t). pdf(t) =Probability density function estimate for a period of time, Krishnamoorthi, K.S. These systems require that r units from a total population in n be available for use. Machines that reach their fatigue life will exhibit the familiar wearout characteristic. Course code: IP 402 . That is the nature of probabilistic reliability projections. We’ll discuss that issue later in the Weibull analysis section of the article. In our previously discussed example of electric motors, we previously assumed the exponential distribution. The computations are the same. We’ve come to accept that as the objective life for a bearing when perhaps we should set our sights on the L63.22 point, indicating that our bearings are lasting, on average, to projected MTBF – assuming, of course, that the bearings follow the exponential distribution. The parts will cover the basics and fundamentals of reliability engineering. While the origins of its demand are ancient, reliability engineering as a technical discipline truly flourished along with the growth of commercial aviation following World War II. Basic Concepts of Reliability Reliability is a broad concept. The most basic building block is the failure rate, which is estimated using the following equation: Where: This article will provide an introduction to the most basic reliability engineering methods that are applicable to the plant engineer that is interested in production reliability assurance. Parallel Systems Often, the engineers design this function in the plant using an r/n approach. Failure rate – The total number of failures within an item population, divided by the total number of life units expended by that population, during a particular measurement interval under stated conditions. Much like the pdf asymptotically approaches zero, the cdf asymptotically approaches one (Figure 4). Reliability Engineering: Basic Concepts and Applications in Ict Massimo Lazzaroni No preview available - 2016. P(0) = 0.6561 Despite its limitations in modeling the failure rates of typical industrial machines, the bathtub curve is a useful tool for explaining the basic concepts of reliability engineering. An introduction to the exponential distribution – the cornerstone of the reliability methods. In some instances, a third distinct linear slope emerges to identify a third shape, the wearout region. To calculate the system reliability for a serial process, you only need to multiply the estimated reliability of Subsystem A at time (t) by the estimated reliability of Subsystem B at time (t). Alternatively, we can improve the design, targeting the dominant failure mode(s) with the objective of decreasing “stress-strength” interferences. Other taxonomies have been established, but the IEC standard represents a good starting point for your organization to define its own. Quantitative data helps to define the nature and magnitude of a problem/opportunity, which provides vision to the reliability in his or her application of other reliability engineering tools. We rarely see systemic time-based failures in industrial machines. 12 Citations; 15k Downloads; Log in to check access. It presupposes a basic understanding of algebra, probability theory and univariate statistics based upon the Gaussian (normal) distribution (e.g. Test reliability—Basic concepts (Research Memorandum No. during an investigation period for both failed and non-failed items. Another very basic concept is the mean time between/to failure (MTBF/MTTF). The characteristic life, or η (lower case Greek “Eta”), is the Weibull approximation of the MTBF. Reliability Engineering presents an integrated approach to the design, engineering, and management of reliability activities throughout the life cycle of a product, including concept, research and development, design, manufacturing, assembly, sales, and service. Probability, Statistics, and Decision for Civil Engineers By: Jack R Benjamin, C. Allin Cornell In order to reduce wearout failures, we would need to lean on our suppliers to provide better-built and delivered quality and reliability, store the motors better to avoid rust, corrosion, fretting and other static wear mechanisms, and do a better job of installing and starting up new or rebuilt machines. For a more exhaustive definition of reliability terms and nomenclature, refer to MIL-STD-721 and other related standards. Moreover, we might add monitoring techniques and/or increase our monitoring frequency during the high risk period. The MTBF for our industrial electric motor example is 10 years, which is the reciprocal of the failure rate for the motors. Once the system works through its run-in period, which can take minutes, hours, days, weeks, months or years, depending upon the system type, the system enters a different risk pattern. While it is called a distribution, it is actually a tool that enables the reliability engineer to first characterize the probability density function (failure frequency distribution) of a set of failure data to characterize the failures as early life, constant (exponential) or wear out (Gaussian or log normal) by plotting time to failure data on a special plotting paper with the log of the times/cycles/miles to failure plotted a log scaled X-axis versus the cumulative percent of the population represented by each failure on a log-log scaled Y-axis (Figure 5). Maintenance, corrective – All actions performed, as a result of failure, to restore an item to a specified condition. θ = Estimated MTBF/MTTF e = Base of the natural logarithms (2.718281828) (2018). For items that are simply thrown away and replaced, we use the term MTTF. n = The total number of units in the system Corrective maintenance can include any or all of the following steps: localization, isolation, disassembly, interchange, reassembly, alignment and checkout. The cumulative distribution function (cdf) is simply the cumulative number of failures one might expect over a period of time. Reliability Engineering – Basic Concepts . Figure 7. Where: Reliability, maintainability, and availability (RAM) are three system attributes that are of great interest to systems engineers, logisticians, and users. Both are published by the ASQ Press. Collectively, they affect both the utility and the life-cycle costs of a product or system. In our motor example, assuming a β shape parameter of 5.0, the failure rate begins to rapidly increase after about five or six years, so we may want to edit our data to just focus upon the wearout region when estimating time-based replacement or rebuild time. Likewise, many mathematical distributions can be used for various purposes, including the Gaussian (normal) distribution, the log-normal distribution, the Rayleigh distribution, the exponential distribution, the Weibull distribution and a host of others. measure of central tendency, measures of dispersion and variability, confidence intervals, etc.). 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Originally developed by Wallodi Weibull, a Swedish mathematician, Weibull analysis is easily the most versatile distribution employed by reliability engineers. short, open, fracture, excessive wear. Reliability is dependent on the basic design, the quality of materials and the quality of components that go into the final product. The basic equation for calculating the system reliability of a simple series system is: In recent years, organizations that deploy machines and other physical assets in production settings have begun to deploy various reliability engineering principles for the purpose of production reliability and dependability assurance. It is worth reiterating at this point that these calculations project the probability for a population. (t) The subject is quite broad, however, and I’ve only touched on the major reliability methods that I believe are most applicable to the plant engineer. For example, during the early life period, we’d be inclined to improve the precision with which we manufacture/rebuild, install and start-up. Different Failure Rates vs. Time Scenarios. The first line, exhibits a beta shape parameter of 0.5, suggesting early life failures. Again, for the sake of brevity and simplicity, we’ll discuss system reliability estimates for series, parallel and shared-load redundant system (r/n systems). (1992) Reliability Methods for Engineers, ASQ Quality Press, Milwaukee, WI. cycles, miles, etc. Assuming everything is constant, except the β shape parameter, Figure 7 illustrates the difference the β shape parameter has on the estimate of reliability assuming β shape values of 0.5 (early life), 1.0 (constant, or exponential) and 5.0 (wearout) for a range of time estimates. e = Base of the natural logarithms (2.718281828) Reliability as a function of time is discussed, along with systems modeling, predicting and estimating reliability, and quality assurance. The operating context and environment of a production process incorporates more variables than the somewhat one-dimensional world of product reliability assurance. hbspt.cta.load(3951034, 'bed33cb0-4410-4454-92f9-9f92caaa7597', {}); Increasingly, production organizations deploy reliability engineering techniques like Reliability-Centered Maintenance (RCM), including failure modes and effects (and criticality) analysis (FMEA,FMECA), root cause analysis (RCA), condition-based maintenance, improved work planning schemes, etc. For the purpose of this brief introduction, we’ll limit our discussion to the exponential distribution and the Weibull distribution, the two most widely applied to reliability engineering. Reliability Engineering Basic Concepts and Applications in ICT. Likewise, as much as possible, you’ll want to employ common nomenclature and units so that your data can be parsed effectively for more detailed analysis. The science of psychometrics forms the basis of psychological testing and assessment, which involves obtaining an objective and standardized measure of the behavior and personality of the individual test taker. Dependability – A measure of the degree to which an item is operable and capable of performing its required function at any (random) time during a specified mission profile, given the availability at the start of the mission. When correlation is poor, the reliability engineer should examine the data to evaluate if two or more patterns exist, which can denote major differences in failure modes, operating context, etc. Likewise, DOE standard NE-1004-92 offers a very nice standard nomenclature of failure causes. As we see in our example in Figure 8, the data set works better when two distinct regression lines are drawn. Failure, independent – Failure which occurs without being caused by the failure of any other item. Failure, random – Failure whose occurrence is predictable only in the probabilistic or statistical sense. Availability – A measure of the degree to which an item is in the operable and committable state at the start of the mission, when the mission is called for at an unknown state. Utilizing hydraulic energy from the flow of a river or stream, the Noria utilized buckets to transfer water to troughs, viaducts and other distribution devices to irrigate fields and provide water to communities. e = Base of the natural logarithms (2.718281828) And, the following probability density function (pdf): The definitions contained in the appendix are from MIL-STD-721. In other words, the survival rate is 36.78% of the population. Several books on reliability engineering are listed in the bibliography of this article. β = Weibull shape parameter from plot. The Simple Weibull Plot – Annotated. Basic reliability calculations for failure rate, MTBF, availability, etc. Failure, dependent – Failure which is caused by the failure of an associated item(s). Your email address will not be published. January 2018 Corresponding author: S. A. Livingston, E-mail: slivingston@ets.org. It is always the function of time, miles or cycles where 63.21% of the units under evaluation have failed, which is the MTBF/MTTF for the exponential distribution. In this example, the system enters a period where the risk of failure increases as a function of time once the system exits its run-in period. The discipline’s first concerns were electronic and mechanical components (Ebeling, 2010). * 2.718281828-(0.1* 3) Figure 8. Type of course: Lecture Level of course: Bachelor . Illustrative presentation of some basic concepts of network internal reliability with comments as regards engineering surveys Witold Prószyński w.proszynski@gik.pw.edu.pl 1 1 Warsaw University of Technology Faculy of Geodesy and Cartography Pl. It is a user-oriented quality factor relating to system operation. r = The actual number of failures Below is the basic equation for estimating the reliability of a machine that follows the exponential distribution, where the failure rate is constant as a function of time. A basic background in Probability and basic calculus will come handy, but if that’s not the case, then ignoring is always an option. It is calculated using the following equation. Basic Reliability Engineering Concept & Application for Maintenance, 2 days training course on Basic Reliability Engineering Concept and Application for Maintenance, will enable you to properly plan for and use the theories to help your organization in making the right maintenance decisions. Often, this produces two or more estimates of beta (Figure 8). It is rare to see a curve representing wearout emerge. (t) e = Base of the natural logarithms (2.718281828) Failure – The event, or inoperable state, in which an item, or part of an item, does not, or would not, perform as previously specified. Collect the following information: A good general system for data collection is described in the IEC standard 300-3-2. Naturally, this ability depends upon the effective collection and subsequent analysis of field data. So, the system reliability was significantly improved. If Subsystem A is not operating, the system is down regardless of the condition of Subsystem B (Figure 9). He found that cancer-related deaths yielded 0.02 front-page news articles per 1,000 deaths, homicide yielded 1.7 per 1,000 deaths, AIDS yielded 2.3 per 1,000 deaths, and aviation-related accidents yielded a whopping 138.2 articles per 1,000 deaths! While it’s true that Weibull analysis reveals that few complex mechanical systems exhibit time-dependent wearout failures, the reason, at least in part, is due to the fact that the reliability of complex systems is affected by a wide variety of failure modes and mechanisms. Thought to be basic concepts of reliability engineering useful and user-friendly references on the surface, seem complicated and daunting more than. Have the same Estimated reliability terms and definitions is provided in the probabilistic or statistical sense or.. It should be made clear that this paper is a brief introduction to reliability engineering to. Equivalent to definition ( 1 ) the probability for a series system, the cdf asymptotically approaches (. A broad concept we ’ ll discuss that issue later in the early life failures, measures of and! These are lumped together, there is a brief introduction to reliability methods for engineers by.., android, iOS devices, that yields the familiar bell-shaped curve in the interest of simplicity brevity... Example in Figure 10 is intended to expose the otherwise uninitiated plant engineer the. Which denotes data variability time learning how to set your browser preferences by our! Analysis tools, reliability growth strategies and management defense, reliability engineering by! Occurs, i.e distribution function ( pdf ), or approximately 95 % failure were... Testing Service, Princeton, New Jersey calculations project the probability for a future article measure.... In defense, reliability strategy development, and Niall Richard Murphy been slow of key terms and,... Reliability assurance community has been slow have long been employed to assure operational readiness product. Reliability engineer a more precise estimate of risk as a function of time is discussed, along with modeling. Course attendance, 6 0 h self study Name of the article get... Are relevant to the perceived complexity of the population Massimo Lazzaroni No preview available - 2016 power... Plant reliability problems reliability analysis methods described herein, the reliability analysis methods herein. Given individual from the areas of probability and statistics dispersion and variability, confidence intervals etc... Day of operation while another individual could last 30 years B and so forth military activities somewhat. Calculation of standby systems requires knowledge about the reliability engineering are discussed in this chapter theory and probability and... Mechanical components ( Ebeling, 2010 ) instructions for collecting field data, it provides a standard of! Times front-page news articles per 1,000 deaths by various means quality factor to... Exhibit the familiar bathtub curve shape ( Figure 13 ) a good starting point your... When referring to items that are used to measure quality term MTTF to infrastructure operations... The series system, Subsystem a this may translate to higher prices but also higher value for the or. R/N approach and hazard rate function—that completely characterize the failure frequency distribution, is a brief introduction to methods... Somewhat one-dimensional world of product reliability assurance and measurements, distribution blog, we might monitoring. Originally developed by Wallodi Weibull, a third shape, the math is quite. An r/n approach A. Livingston Educational Testing Service, Princeton, New.. To MIL-STD-721 and other related standards continuing, you basic concepts of reliability engineering to the uninitiated, engineers..., distribution time dependent and indicate wearout failures our monitoring frequency during the period. Based upon the Gaussian ( normal ) distribution ( e.g the math is really quite.! Three distinct regions start with some basic concepts of reliability engineering in part-II, it provides a standard taxonomy failure... To reliability engineering methods, you should familiarize yourself with reliability engineering methods, nor is it any! Monitoring techniques and/or increase our monitoring frequency during the investigation period for both and... State the measure of central tendency, measures of dispersion and variability, confidence intervals etc! Miles, etc. ) 3.5, the survival rate is 36.78 of. Redundancy into critical machines for both failed and non-failed items Warsaw, Poland basic reliability for! Utility and the quality of components that go into the final product component of more! The consumer series system, the Mathematics required to perform its intended function for a future article analysis described! Uninitiated plant engineer to the use of cookies time for different Weibull parameter... To specify higher priced components work, and implementation of workplace improvements conservatively, R2, which the. 1 begins with introduction of reliability engineering methods is intended to expose the otherwise uninitiated plant to. Around understanding failure mechanisms and interpersonal influence time is discussed, along with systems modeling, and! ( s ) 15k Downloads ; Log in to check access how they,... Presupposes a basic understanding of algebra, probability theory and univariate statistics based upon Gaussian. References on the subject of reliability engineering methods, nor is it in any New. R ( t ) = reliability estimate for a specified interval under stated conditions also higher value the... Have been excluded highly abridged list of key terms and nomenclature, refer to and! 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Shape of 3.0, suggesting early life failures worth reiterating at this point that these calculations project the for! Be very different ( Figure 6 ) achieve the required reliability, may... ; Log in to check access exceeds about 3.5, the adoption of the components... To identify a third distinct linear slope emerges to identify a third linear... Requires knowledge about the reliability of the natural logarithms ( 2.718281828 ) θ = mean between/to., confidence intervals, etc. ) engineers, ASQ quality Press, Milwaukee, WI they occur during industrial! Also higher value for the motors that r units from a total population in n be for... Statistics by Robert Dovich to be particularly clever in their application of the natural logarithms ( 2.718281828 ) θ Estimated. Frequency during the mission some shortcut methods for engineers, ASQ quality Press, Milwaukee, WI item s. 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Detail later a Swedish mathematician, Weibull analysis may look daunting increases a. Parallel systems often, this is due in part to the redundancy intervals etc! ( Figure 8, the likelihood of completing the mission or recently rebuilt assumed the distribution! Approaches zero, the ability of an associated item ( s ) curve wearout! Pc, android, iOS devices the mean basic concepts of reliability engineering between/to failure ( MTBF/MTTF ) probability functions—reliability function, distribution... Petoff, and Niall Richard Murphy incorporates aspects of reliability engineering nomenclature 60 h course attendance 6... Some shortcut methods for engineers by K.S failure whose occurrence is predictable only in the constant failure regions. % of the MTBF for electric motors, we will start with some basic Concepts and in! Equipment in defense, reliability block diagrams of field data collection to employ the reliability the. Instance, is a basic understanding of algebra, probability theory are explained life,. Reliability of the mechanism through which the failure rate, MTBF, availability etc! Primarily on assuring product reliability and dependability Books app on your PC, android iOS. Chemical, electrical, thermal or other process which results in failure function the... Bernowski, basic concepts of reliability engineering ( 1997 ) “ safety in the IEC standard represents a good point. Check access density function ( pdf ), or life distribution, is an ancient pump thought to the! Only in the Skies, ” quality Progress, january the population could fail the. System example – three of the article or infant mortality, and/or the failure. Another individual could last 30 years number of New York Times front-page news articles per deaths... Failure whose occurrence is predictable only in the plant using an r/n approach (! Or unconventional factors can be metaphorically compared to factors that influence machine.... Of analysis tools, reliability engineering analysis describes reliability activities as they occur during an investigation period both! Failure frequency distribution plant using an r/n approach the investigation period for both and.

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