Your Reliability Engineering Professional Development Site
Unless you live in Fantasyland, there’s no silver bullet for achieving your equipment Reliability goals. Start at the beginning, with Reliability Centered Maintenance and watch your Reliability program come to life. [Read more…]
There is a type of error when conducting statistical testing that is to work very hard to correctly answer the wrong question. This error occurs during the formation of the experiment.
Despite creating a perfect null and alternative hypothesis, sometimes we are investigating the wrong question. [Read more…]
Fatigue regulations and guidelines have been long established in aviation, transportation and the nuclear industries (just to name a few). The science is solid supporting the correlation between human fatigue, and poor decision-making/poor responsiveness.
So why aren’t such fatigue regulations required in healthcare as a matter of standard like in other industries? Is there something different about the physiology and/or anatomy of a healthcare worker versus a pilot, truck/bus driver or nuclear operator? [Read more…]
Some time ago when talking with someone I just met, the conversation turned to what we did for a living. I mentioned being a reliability engineer, and his response: “Oh, yes, we do reliability”. Curious, as I’m not sure that I ‘do reliability’, we then talked about what he meant.
The conversation revealed that they had a list of tasks that they accomplished for each product under development. They did tests and reviews of the results. A lot of testing. They did FMEA and HALT. He believed the engineers did derating or stress/strength calculation. He didn’t know about process stability with vendors or internal manufacturing lines.
They did stuff, which meant they did reliability.
Changes are a part of the evolution of a new design. But managing the timing of changes is important. Figure 1 shows that the cost of making design changes increases rapidly beginning late in development. In well-run projects, design changes are mostly complete by early development. But project teams that ignore reliability often discover the need for changes during lab testing (late development) or commercialization. This is very costly, creates schedule delays, and can lead to brand damage. In Maximizing Oilfield Equipment Reliability, it is stated that Design for Reliability (DfR) programs are used by OEMs to elevate reliability. But DfR activities can also reduce the cost of changes. How is this achieved? [Read more…]
Ever wonder how some organizations make their vibration or thermographic program work, and not only work but deliver huge results to their organization? They use a systematic approach to establishing the correct frequencies of inspection. Establishing the correct frequencies of maintenance activities is critical to the success of any maintenance program. Too infrequently and the organization is subjected to failures, resulting in poor operational performance. Too frequently, and the organization is subjected to excess planned downtime and an increased probability of maintenance induced failures.
This article will continue the discussion on establishing the correct frequency in a maintenance program. There are three different approached to use, based on the type of maintenance being performed;
This article will focus on On-Condition Maintenance. While establishing the frequency for Fixed Time Maintenance activities is complex and is more of science, establishing the frequency for Condition Based Maintenance inspections (or On-Condition) is a mix of science and art.
The first step to determining the inspection frequency for on-condition tasks is to construct the P-F curve and P-F interval. Constructing a P-F curve requires recording the results of the inspection and plotting the result versus the elapsed time. If enough measurements are taken, a fairly consistent curve can be developed for each failure mode. Making sure that the data is gathered carefully and consistently will aid in increasing the quality of the P-F curve. Lets use an example from RCM2;
Now this works quite well for linear P-F curves because it is predictable. So how do you construct a P-F curve for a non-linear failure mode? It is a bit more complex, and a bit more of art. Let’s use another example;
With P-F curve and P-F Interval (PFI) established, the frequency can be determined.
Once the P-F Interval (PFI) is established, the inspection frequency can be determined. Thankfully it is not as complicated as establishing Fixed Time Maintenance frequencies. To determine the inspection frequency, the formula is either PFI/3 or PFI/5.
Now the above works well for linear P-F curves, so how do you establish the frequency for the non-linear curves? You use the same approach as above for the initial inspection frequency.
However, once a potential failure is detected, additional readings should be taken at progressively shorter intervals until a point is reached that a repair action must be taken. For example; the initial inspection frequency is every four weeks. Once a defect is detected, the next inspection will be at three weeks, then two weeks and then ever week.
This is only guidelines and should be adjusted based on the method used to track and trend data, the lead time of the repair parts (if not kept on site), and how quickly the data will be analyzed, and the repair work planned. If your planning process is poor, the frequency should be more frequent, to allow for a high chance of detection sooner.
How much thought was put into your Condition Based Maintenance inspection frequencies? Have you broken down each failure mode trended the data and established the frequency using a systematic approach? As with the Fixed Time Maintenance activities, you may be over or under inspecting, costing your organization reliability or money.
Remember, to find success; you must first solve the problem, then achieve the implementation of the solution, and finally sustain winning results.
I’m James Kovacevic
Eruditio, LLC
Where Education Meets Application
Follow @EruditioLLC
References;
Anyone who knows me knows that I tend to only think in terms of cars. I can remember the car someone pulled up in at a party four years ago, but will have no recollection of what their name was. Moreso, I view culture, politics and economics through a sort of automotive anthropologist lens. For example, darker colors are more popular in luxury car sales when an economic downturn has occurred and major shifts in industrial focus will be reflected in increased offerings of economy cars that can hold 4 to 5 people. I think you can see what the problem is here.
In any case, I came up with a cooking analogy (in no way automotive related) for a principal of data organization and I have to say, it’s actually pretty good! So, I am documenting it here.
[Read more…]
Fifty years ago, having your own car was a sign of adulthood and your ticket around town. But that is all going to change within the next five to ten years due to rising CO2 levels and a new trend called Transportation as a Service. TaaS sits at the intersection of four technical macro trends. These are:
These trends are here today and are predicted to grow significantly and quickly over the next five to ten years. It is a positive trend with a lot of positive affects on the country and world.
The risk to this trend is the need for electric power will outstrip the supply. This article presents the case for this risk. [Read more…]
… is the world’s leading method for identifying maintenance and other activities required to sustain reliable performance of physical assets. Previously I discussed the various maintenance approaches you can use. This method (RCM-R®) is a structured approach to making those choices. If you want a proactive maintenance program that really works, then Reliability Centered Maintenance is the most thorough approach you can take to get there.Since the 1970’s RCM (generic) has been responsible for huge improvements in airline flight safety – crash rates today are 1 / 120th of what they were before RCM, and the costs of aircraft maintenance programs are way down. We are all comfortable flying in safety. That would not be the case had RCM not come along. [Read more…]
One of the most important concepts in designing for reliability is robust design. This article is a high-level overview of robust design and its relationship to FMEA.
“For the robust, an error is information.” Nassim Nicholas Taleb
It is often wrongly believe that ALL Failure Modes should be included in an RCM analysis. RCM gives us four specific criteria that dictate what Failure Modes should be in included in a properly executed RCM analysis. They are… [Read more…]
A common question when setting up a hypothesis test is concerning sample size. An example, might be: How many samples do we need to measure to determine the new process is better than the old one on average?
While this seems like a simple question, we need a bit of information before we can do the calculations. I’ve also found that the initial calculation is nearly always initiated a conversation concerning the balance of sample risks, the ability to detect a change of a certain size and the constraints concerning the number of samples. [Read more…]
[Editor: originally posted Jan 23, 2015]
For those that are football enthusiasts and looking forward to the upcoming Superbowl, we are intrigued by the recent scandal in the NFL. The scandal involves the allegation that somehow the New England Patriots’ footballs used in the game against the Colts last week, were deflated and did not meet the minimum PSI requirements of the NFL to be ‘legal’ for game use. The allegation involves the possible tampering of the NE footballs to attain that ‘deflated’ state. Conceivably this would make it more desirable to throw and catch in the conditions of the game. [Read more…]
Some time ago, earlier in my career, I worked for a wonderful boss. She would stop by my office on occasion and ask ‘what’s new?’ or “how’s it going?’ Just a check-in. I often let her know about the current vexing problem I was struggling with at the moment.
The funny thing is she never directly solve the problem for me. She certainly could have. Instead, she would ask a couple of questions that always helped me to find the solution. This happened with problems concerning dealing with a difficult person, strange material properties, motivating change within a group, or finding someone that could design and run a computational fluid dynamic model for me.
It was her questions the helped. She did this in meetings, in presentations, and when she swung by my office for a chat. [Read more…]
Think about your maintenance program. How often are your PMs scheduled? How were those frequencies established? If you are in the majority, the chances are that the frequencies were either established from the OEM manual, or by someone in the department without data.
Establishing the correct frequency of maintenance activities is critical to the success of any maintenance program. Too infrequently and the organization is subjected to failures, resulting in poor operational performance. Too frequently, and the organization is subjected to excess planned downtime and an increased probability of maintenance induced failures. So how do you establish the correct maintenance frequencies for your organization? There are three different approached to use, based on the type of maintenance being performed;
This article will focus on Time Based Maintenance Tasks.
“The frequency of a scheduled task is governed by the age at which the item of or component shows a rapid increase in the conditional probability of failure” (RCM2). When establishing frequencies for Time Based Maintenance, it is required that the life be identified for the component based on data.
With time-based failures, a safe life and useful life exists. The safe life is when no failures occur before that date or time. Unless the failure consequence is environmental, or safety related, the safe life would not normally be used. The useful life (economic life limit), is when the cost of consequences of a failure starts to exceed the cost of the time-based maintenance activity. There is a trade-off at this point between the potential lost production and the cost of planned downtime, labour, and materials.
So how is the safe life or useful life established? It is established using failure data and history. This history can be reviewed using a Weibull Analysis, Mean Cumulative Failure Analysis or even a Crow-AMSAA Analysis to statistically determine the life of the component. Once that life is determined using a statistical analysis, the optimum cost effective frequency must be established.
This formula is used to establish the economic life of the component, balancing the cost of the downtime vs. the cost of the replacement.
Where;
The formula will provide the total cost based on the maintenance frequency. Since the calculation can be time-consuming, Dodson developed a table which can be used if;
Therefore when using the table, use formula; T=mѲ+δ. Where;
In the example below, you can see how the table can be used with the formula;
The cost for a PM activity $60. The cost of a failure for the same item is $1800. Given the Weibull parameter of B=3.0, O=120 days, and δ =3 how often should the PM be performed?
The table value of m given a shape parameter B of 3.0 is 0.258. Therefore;
As you can see, determining the frequency of Fixed Time Maintenance tasks is not as simple as picking a number out of a manual or based on intuition. Armed with this information, a cost effective PM frequency based on data can be developed for your Fixed Time Maintenance tasks. This will ensure the right maintenance is done at the right time, driving your plant performance further.
Does you Fixed Time Maintenance Tasks have this level of rigor behind them? Why, not? After all, your plant performance (operational and financial) depends on it. Stay tuned for next week’s post on establishing frequencies for On-Condition tasks.
Remember, to find success; you must first solve the problem, then achieve the implementation of the solution, and finally sustain winning results.
I’m James Kovacevic
Eruditio, LLC
Where Education Meets Application
Follow @EruditioLLC
