Here’s Fred on a Dare to Know podcast episode talking about the book and blogging about the issues and solutions concerning MTBF. You can learn more about Fred at his bio.
The Reliability Metric: A Quick and Valuable Improvement Over MTBF
Search Results for: mtbf
MTBF and preventative maintenance
I find the world of maintenance a very odd place to find MTBF. While it is possible, that a set of equipment or a machine may actually have a constant failure rate it is the exception rather than all that common. Assuming a constant failure rate doesn’t make it so. [Read more…]
NoMTBF Campaign Outfitters
Start the discussion. Encourage those around you to consider why and how they are using MTBF.
At one point, someone noticed I was pretty adamant around this topic and after mentioning it was my personal mission or I was mounting a campaign to get rid of MTBF, they suggested creating campaign buttons. Those buttons have now evolved into a full fledge store. Get your t-shirts, jackets, earrings, coffee mug, and, of course, buttons at the CafePress NoMTBF store.
[Read more…]Linking Reliability Concepts and Safety Performance
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 time variable is crucial in calculating the reliability of a system. Reliability is the Probability of Success. And 1 minus the Probability of Failure.
[Read more…]
5 Reasons Rate of Change is Important
A simplifying assumption associated with using MTTF or MTBF implies a constant hazard rate. Some assume we’re in the useful life section of the bathtub curve. Others do not understand what assumptions they are making.
Using MTTF or MTBF has many problems and as regular reader here know, we should avoid using these metrics.
By using MTTF or MTBF we also lose information. We are unable to measure or track the rate of change of our equipment or system’s failure rates (hazard rate). The simple average is just an average and does not contain the essential information we need to make decisions.
Let’s explore five different reasons the rate of change of a failure rate is important to measure and track. [Read more…]
QDD 165: Redux: 5 Aspects of Good Reliability Goals and Requirements
5 Aspects of Good Reliability Goals and Requirements
Good reliability requirements are going to drive our design decisions relating to the concept, the components, the materials, and other stuff. So, the moment to start defining reliability requirements is early in the design process. But, what makes a well-defined reliability requirement? There are five aspects it should cover: do you know what they are?
We’ll describe what makes a good reliability requirement and examples of common (but not good) requirements.
How We Think About Reliability
How We Think About Reliability Is Important
Getting on an airplane we think about the very low probability of failure during the flight duration. This is how we think about reliability.
When buying a car we think about if the vehicle will leave us stranded along a deserted stretch of highway. When buy light bulbs for the hard to reach fixtures we consider paying a bit more to avoid having to drag out the ladder as often.
When we consider reliability as a customer does, we think about the possibility of failure over some duration.
And, we really don’t like it when something fails sooner than expected (or upon installation). [Read more…]
Fundamentals of Metric Monitoring
An Accendo Reliability recorded webinar event
Following along the idea stated by Lord Kelvin, “…when you can measure what your are speaking about, and express it in numbers, you know something about it…”, we have organizations measuring reliability performance. Not that measuring something is managing it, those are two different activies. Yet, using various metrics that we track on a regular basis does provide some useful information if done well.
Let’s explore a few ways that I’ve seen reliability metric monitoring. Let’s also examine a simple process to establish, maintain, and end metrics. Measuring something has an expense, so it must also provide value. If the value is not there, or it’s not useful for making decisions, then either improve the metric system or end the metric.
[Read more…]How to Define Proper Product Reliability Goal
Defining a proper product reliability goal is a critical step in ensuring that a product meets customer expectations and performs adequately throughout its intended lifespan. This also involves a careful balance between the required level of reliability and the associated costs and complexities of achieving that reliability.
[Read more…]The Worst Reliability Requirement
by Mark Powell
Most of us have seen reliability specified using a requirement like the following:
The Zeus 5000 SUV shall have an MTBF of 144,269.5 miles with a 90% confidence.
Some readers may not have seen reliability requirements specified in any other way. What they have always seen has read something like: The widget shall have an MTBF of X with a Y% confidence. This reliability requirement structure is rather ubiquitous
in military and aerospace specifications, which along with Mil-HDBK-217, have been major influences in reliability specification practices for decades in many industries.
Renewal vs. Generalized Renewal Process?
How to distinguish a renewal process from a “generalized” renewal process? Compare observed monthly returns vs. actuarial returns forecasts using actuarial return rate estimates of TTFF and TBF (Time To First Failure and Time Between Failures). A geophysicist masquerading as an Apple reliability engineer said, “It’s too hard to figure out the probability that a return came from a computer made in an earlier year.” It’s harder if returns could be second, third, or???
[Read more…]How Often Should You Schedule Preventive Maintenance?
Ever wondered how often you should perform preventive maintenance tasks? In just 31 seconds, learn the key concept of Useful Life and how it determines the intervals for Scheduled Replacement and Scheduled Restoration tasks. And learn that Mean Time Between Failures (MTBF) does not govern how often you do them.
[Read more…]The Fear of Reliability
MTBF is a symptom of a bigger problem. It is possibly a lack of interest in reliability. Which I doubt is the case. Or it is a bit of fear of reliability.
Many shy away from the statistics involved. Some simply do not want to know the currently unknown. It could be the fear of potential bad news that the design isn’t reliable enough. Some do not care to know about problems that will require solving.
Whatever the source of the uneasiness, you may know one or more coworkers who would rather not deal with reliability in any direct manner.
[Read more…]
Using Crow-AMSAA Plots in Disaster Predictions
Crow-AMSAA Analysis Overview
Crow-AMSAA Plots have a variety of names, such as Reliability Growth Plots or Duane Plots. The term “Crow” comes from Dr Larry H. Crow, who enhanced James T. Duane’s pioneering launch of this methodology, which was developed in the early 1960s (1). Crow successfully applied the method in the US Army Materials System Analysis Activity (AMSAA). The technique has blossomed into large amounts of new applications in industry such as but not limited to:
- Making reliability more visible and manageable hence contributing to Reliability Improvement Programs,
- Monitoring Design Optimization and Quality Performance,
- Catastrophic or adverse event occurrence predictions and trends which in essence are the objective of this article.
In practical terms, The Crow-AMSAA technique involves plotting, most commonly, cumulative failures vs cumulative time on a log-log scale resulting in straight line plots (2). The line slope value (or Beta value) indicates improving, deteriorating, or constant failure occurrences. Due to the straight-line nature of the plots, future failure forecasts can be estimated. In plain words, based on the current trend, when is the next failure expected to occur? This method handles mixed failure modes, so it is, therefore, suitable for the complex nature of the generating units. [Read more…]
The Army Memo to Stop Using Mil HDBK 217
Over 20 years ago the Assistant Secretary of the Army directed the Army to not use MIL HBK 217 in a request for proposals, even for guidance. Exceptions, by waiver only.
217 is still around and routinely called out. That is a lot of waivers.
Why is 217 and other parts count database prediction packages still in use? Let’s explore the memo a bit more, plus ponder what is maintaining the popularity of 217 and ilk.
[Read more…]