Your Reliability Engineering Professional Development Site
A listing in reverse chronological order of these article series:
In probability theory and statistics, the Weibull distribution is a continuous probability distribution. It models a broad range of random variables. Largely in the nature of a time to failure or time between events. It addresses mechanical or structural failures in the field of Reliability Engineering. By nature, the Weibull distribution provides a lot of information such as aging characteristics or expected asset lifetime. One of its most common outputs is the Bathtub Curve.
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Physics-of-Failure warns us to keep the sum of all static and cyclic loads on a part’s microstructure below its fatigue stress limit.
The image below shows two example metal fatigue limit failure curves. These curves were determined based on controlled laboratory experiments. These experiments use a machine with a fixed load to test the selected piece’s microstructure stress levels. Curve A shows that at a high stress level, close to the Ultimate Tensile Strength of steel, the test piece failed after 10,000 cycles. As the fatigue stress level is reduced, the test piece lasts longer. When the imposed stress is limited to around 50% of the UTS, the cycles to failure had no measurable limit. On the other hand, Curve B shows that at all levels of fatigue stress the component would eventually fail. However, the same outcome can be seen, that as stress reduces the service lifetime before failure increases.
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Have you ever tried to implement any asset improvement activity but it didn’t go so well? Couldn’t rally the troops? Couldn’t get the kind of management buy-in that you really needed to get things off the ground? If so, you’re not alone.
I’ve read too many articles describing that up to 70% of asset improvement initiatives fail. And I think it’s because a lot of people don’t have a basic understanding of maintenance and reliability principles. So they don’t understand why “change” needs to take place.
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Focus on failure elimination, otherwise equipment failures never stop because they are forever being introduced and perpetuated by poor procedures and practices, poor quality control and poor business management systems.
Knowing defects cause future equipment failures, production downtime, unnecessary costs and lost profits, it is necessary to put defect elimination strategies into place to purposely stop defects occurring and to remove the defects that are already present.
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In our first two videos we discussed alarms and event rates. Today we will be discussing rework. What is rework? How can we identify rework? George has it covered. Check it out this latest video and if you have any questions feel free to leave a comment!
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Failure Modes and Effect Analysis (FMEA) is an excellent foundation for Reliability Programs. It is also a stepping stone to build Reliability, Availability, and Maintainability (RAM) models. Here lies the “beauty” of doing Reliability and Maintenance analysis. Whereby information from one analysis can help enhance another analysis.
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Plant and equipment failures are business process failures. Plant stoppages and breakdowns result from failure-causing practices built into business processes and from leaving the right reliability practices out of them. Processes may superficially look okay because they have documentation, charts and records, but if you suffer a steady stream of failures, problems, and rework, then your processes contain unforeseen ‘traps’ into which your people and equipment regularly fall. Failure was not intended when your processes were chosen and designed, but failure is what happens when they are used.
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Air, sea, space, land, or underground? Commercial, government, or military? Reliability Centered Maintenance has something for everyone!
Absolutely. In fact, in Stanley Nowlan and Howard Heap’s book on RCM, they state:
The content of scheduled-maintenance programs developed by experienced practitioners of MSG-2 techniques may be quite similar to the programs resulting from RCM analysis, but the RCM approach is more rigorous, and there should be much more confidence in its outcome. The RCM technique can also be learned more quickly and is more readily applicable to complex equipment other than transport aircraft.
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In most industries we ideally want the lowest-cost maintenance strategy, one that balances risk of unplanned vs planned maintenance costs to a lifetime minimum.
This is what we’ve calculated in a previous article HERE, and this article/exercise is a follow-on from this.
The downside of using this method is that it may select a maintenance interval where the inherent reliability of the component at changeout time is less than is required for operational reasons, or that we’re not getting the best “increase in reliability vs marginal cost” value. [Read more…]
First master the fundamentals
Basketball Olympic Gold Medallist Larry Bird
The industrial world today is abuzz with a lot of terminologies and jargons mainly stemming from today’s technological advances in the areas of sensors, data, communication and electronics. Each day brings in something new for the Asset Owners from the service providers who claim that their technology, product or service is ‘unique’ and has been ‘never seen before’. While a lot of these offerings are innovative in many aspects, the real question lies in how do they fit within the ‘fundamentals of the Asset Management’? [Read more…]
Companies that want plant and equipment reliability need to engage the people in the workplace and give them a large degree of responsibility for improving the performance of their equipment. The most successful solution yet discovered to do that is the autonomous work team.
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Last time we discussed Alarms in the Opportunities for Maintenance and Reliability series. This week we will be discussing event rates. What is an event rate? Watch George break it down!
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Concurrent or simultaneous failures can happen with redundant or spared systems. This means that both spared equipment can fail at the same time leaving the operator with no production output. For example, we have two alternating pumps operating in a parallel configuration. Each one acts as a spare and at any one time can take over if the other one fails. This article is based on a question I was asked during a recent industry presentation. I thought the example was interesting and informative enough to share with the Maintenance and Reliability community.
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The world needs plant and equipment that are reliable and fault-free for decades. Yet Maintenance can only keep machinery working by replacing broken and at risk parts. Even industrial asset management only aims to lower the cost of plant and equipment ownership. Neither methodology has the capability to deliver what mankind needs in future. Before the end of this century both disciplines will die-out because intelligent production machines will be made that are completely reliable and maintenance-free for their entire lifetimes.
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In this video, we use RCM principles to decide if I should accept the consequences of failure or visit the dentist to eliminate the Failure Mode.
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