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Reliability Engineering – It’s all about Models!

Definition of Reliability

The concept of Reliability is often misused, misunderstood, and misinterpreted. Reliability in its academic root, is defined as the probability that a system will perform its intended function in a specified mission time and within specific process conditions. So, it is in essence a probability.

The ageing variable is crucial in calculating the reliability of a system. Reliability is the Probability of Success. And 1 minus the Probability of Failure. In the equation below , the ageing variable is time (t).

$$ \displaystyle \large R\left(t\right) = 1 – F\left(t\right) \:\:\:\: (where \: F = Failure \: Probability) $$

Reliability engineering is based on building data models to predict future system performance accurately. Based on past performance records. The model is more or less precise depending on how many past records we have. The more data, the more precise the model. At the end of the day, a well defined model, even with a little data, is better than no model. At least we can proceed in the right direction. That is, make the best possible decision for our assets.

This article looks at a non exhaustive list of models in the Reliability Engineering realm.

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by nomtbf Leave a Comment

The Damage Done by Drenick’s Theorem

Have you ever wondered by we use the assumption of a constant failure rate? Or considered why we assume our system is ‘in the flat part of the curve [bathtub curve]’?

Where did this silliness first arise?

In part, I lay blame on Mil Hdbk 217 and parts count prediction practices. Yet, there is a theoretical support for the notion that for large, complex systems the overall system time to failure will approach an exponential distribution.

Thanks go to Wally Tubell Jr., a professor of systems engineering and test. He recently sent me his analysis of Drenick’s theorem and it’s connection to the notion of a flat section of a bathtub curve.

Wally did a little research and found the theorem lacking for practical use. I agree and will explain below. [Read more…]

by Semion Gengrinovich 1 Comment

Software Reliability

Software reliability and hardware reliability are two distinct concepts within the field of engineering, each with its own unique characteristics and measurement challenges.

Software reliability is defined as the probability that software will operate without failure for a specified period of time in a specified environment. It is a reflection of the design perfection rather than manufacturing perfection, which is more associated with hardware reliability. The complexity of software is a major contributing factor to software reliability issues. Unlike hardware, software does not degrade over time or wear out, but it may have faults due to design defects that can cause failures.

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by Mike Sondalini Leave a Comment

Aiming for Operational Excellence

The aim of being in business is to satisfy customers in ethical ways while making a profit. To achieve this, variable and fixed costs should be as low as possible without sacrificing on quality products or customer experience.

The term Operational Excellence is often used to refer to a range of technical, soft-skills, and culture components. Regardless of how it is phrased, the core definition and goal are the same – to produce better operational results, and create value for customers and shareholders. In short, Operational Excellence performance is to produce the best quality products or services customers will buy for the lowest expenditure to maximize operating profit. The most successful businesses have built systems and processes that automatically keep their costs low and profits high

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by Greg Hutchins Leave a Comment

VUCA, Distruption and Risk

Breaking an old business model is always going to require leaders to follow their instincts. There will always be persuasive reasons not to take a risk. But if you only do what worked in the past, you’ll wake up one day and find that you’ve been passed by.

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by Hemant Urdhwareshe Leave a Comment

Response Surface Designs: Part-1 Addition of Centerpoint

Dear friends, I am posting a video after some gap! This is our first video in our series on Response Surface Designs. Response Surface Designs become necessary when we want to model a second order response in an experiment. In this first video, Hemant Urdhwareshe explains addition of centerpoint to a factorial design to assess presence of non-linearity in the response. The concept is explained with a virtual catapult with a two-factor two-level design.

Links to the related videos:

(1) DOE-1: Introduction to Design of Experiments

(2) DOE-8: Linearity and Orthogonality in Experimental Design

(3) DOE-6: Case Study in Creating Full Factorial Design in Minita b

(4) DOE-7: Analyse Factorial Design with Minitab

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by Nancy Regan Leave a Comment

The Standard for Reliability Centered Maintenance (RCM)

What Is SAE JA1011? The International Standard for Reliability Centered Maintenance (RCM)

In today’s video, I explain SAE JA1011, the internationally recognized standard that sets the minimum criteria for any process to be called Reliability Centered Maintenance (RCM). Published in 1999, this 12-page document was created to ensure that the term “RCM” is used correctly, following the original principles defined by Stanley Nowlan and Howard Heap. If you’re ever presented with a process claiming to be RCM, SAE JA1011 is your go-to reference to verify that the process is True RCM.

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by Semion Gengrinovich Leave a Comment

Design Change Implementation

Once a problem is clearly identified, the team must gather information concerning the problem, and identify potential solutons. After evaluating the potential solutions, the team can select the solution that will solve the problem effectively. It is then time to plan the details on the design change implementation.

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by nomtbf Leave a Comment

3 MTBF Stories

Everyone loves a great story. Storytelling has been a long tradition to pass along knowledge and wisdom.

There are good stories, tales of inspiration. There are sad stories, tales of caution.

There are fables, ghost stores, legends, epic poems, and more. When considering the reliability performance of your product or equipment, you probably have a few stories that you can tell. “That time … “

Simple join colleagues for lunch and ask about the ‘major disasters’ of the past. The stories help us to remember and hopefully avoid repeating mistakes.

Here are three stories with MTBF as a central figure. It is a site and blog that does take about MTBF, so it fits. To start, let me introduce you to Martin, a new reliability engineering reporting to his first day of work at a bicycle design and manufacturing company. Two sad stories and a good one. enjoy. [Read more…]

by Mike Sondalini Leave a Comment

Machines only Stop Working after their Parts Fail

The level of care given to an equipment item depends directly on the size of business risk if it fails. Reduce the chance of its failure and you increase its reliability. It becomes vital to know the full range of risks each part within an equipment item will suffer. The right asset management strategy starts by knowing which parts are at risk and it is completed when the necessary actions to prevent all failures are in use. Asset Management that does not identify all the risks to equipment parts when selecting equipment maintenance and operating strategies will get you doing the wrong work.

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by Greg Hutchins Leave a Comment

Communication Skills Really Matter

Guest Post by Bill Promfret (first posted on CERM ® RISK INSIGHTS – reposted here with permission)

Back in 1990, I was introduced to Og Mandino, a best selling American author, just three of his books, “The Greatest Salesman in the World” The Greatest Miracle in The World” and “The Greatest Secret in the World” these three books alone sold over 50 million copies, his lecture was on “How to write and Speak.” In his presentation, which had been a tradition for more than 40 years, was posted on YouTube not long after his death in 1996. In it, he explains the relationship among three critical elements of any level of success: knowledge (K), practice (P) and talent (T).

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by James Reyes-Picknell Leave a Comment

Gremlins Today

“Gremlins today” is a series of short articles on problems that plague industrial operations the world over.

Originally, Gremlins were fictitious mischievous trouble makers who caused Royal Air Force aircraft breakdowns during World War II. Author Roald Dahl published a book about them in 1943, based on his own experience as an RAF pilot. Pilots in the RAF used to carry lucky Gremlins to ward off their effects. Dahl worked with Disney to publish a cartoon book based on them, but it never made it into a movie at the time. Never-the-less, it did loosely inspire the 1984 movie, “Gremlins,” by Steven Spielberg.

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by Joe Anderson Leave a Comment

The Power of Vision in Leadership and Organizational Success

All Things Rise and Fall on Vision—or the Lack Thereof

In leadership, vision is everything. It’s the guiding star that directs decision-making, inspires action, and shapes the future of an organization. Whether in business, maintenance, or any other field, a clear and compelling vision can determine the trajectory of success or failure. Without it, even the most well-intentioned efforts can flounder. The power of vision in leadership and organizational success cannot be overstated. In essence, all things rise and fall on vision—or the lack thereof.

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by Hemant Urdhwareshe Leave a Comment

SPC-2: Proportion Defective and Number Defective charts (p and np charts)

Dear friends, we are happy to release this second video on statistical process control charts. In this video, Hemant Urdhwareshe illustrates how to use attributes charts, specifically p-charts for proportion defective and np charts for number defective! Watch our video SPC-1 for Introduction and Selection of Control Charts, and X-bar and R charts.

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by Nancy Regan Leave a Comment

Is a Formal Criticality Analysis Necessary?

Do You Need a Formal Criticality Analysis to Select Equipment for RCM? In today’s video, I answer a common question: is a formal criticality analysis required to determine what equipment should undergo Reliability Centered Maintenance (RCM)? While you can perform a formal criticality analysis, it’s not always necessary. One of the best ways to get started with RCM is to focus on equipment that causes chronic downtime or has the highest costs. Starting small with pilot projects on your highest pain points is a practical approach. Join me in beautiful Santiago, Chile, as I share how common sense can guide your RCM efforts, ensuring you get the reliability you need without overcomplicating the process.

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