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by Rolly Angeles, Reliability Consultant
Have you ever figured it out why our equipment keeps on failing despite our best efforts on our Preventive Maintenance ? I have a list of questions below and try to answer them honestly on your own.
You are always press for time and you do not have the luxury of time to attend to training because your boss will not allow you to attend to them, am I right here ?
Do you need to turn on your cell phone at night to received late calls from other shifts wanting you to go to the plant in the middle of the night or early morning for a problem they seem can’t fix ?
Do you hear this often from your people that they are always outnumbered by the failures and maintenance are always complaining that they lack the manpower resources to fix all failures ?
Do you have to sacrifice some family time in order to keep working overtime and when you return home everyone is asleep ?
When an equipment is newly overhauled or just perform a major Preventive Maintenance overhaul, do you ever wonder why operators always complain why it ain’t running and make a grin on his/her face and say “ No wonder this machine ain’t running, it’s newly overhauled” ?
Do you need to cannibalized some parts from other station-nary equipments since there is no stock or spare around the stockroom ? Do you do this all the time ?
Now this is the worst part, do you have nightmares of your work or your boss yelling at you that wake you up in the middle of the night ?
Then if you answer YES to almost all of these questions, don't be surprise, you are not alone in this world !
Let me explain to you, when I was still studying all these stuff about reliability and maintenance, I use to have a friend and mentor, who have worked for a very long time in an industry, they retire him because he is old. I guess that would be the trend. But anyway, I remember asking him what was the best maintenance strategy that we can adopt and he told me that if I wanted to know the answer to my question then he said to come with me and take a walk, and so we walk and sat down on a park near his place. The park had a basketball court and he ask me to sit down and watch the game of basketball since there was an ongoing league at that time. We sat and watch the game and not a single word from him was ever spoken. We just watch the game. The basketball game ended and it was getting a little dark and he told me to go home since my place is far from here. I told him, why we watch this game and ask him that I though you are going to answer my question about the best maintenance strategy to adopt. Calmly, he look at me smiled and said, Rolly, if you watch the game carefully, then you have already answered your question. I was shocked, since I really have no idea what he meant when he said that.
I usually give this story to people whom I teach and wonder for a while if they can figure it out themselves. I guess like me they find a hard time what that old man was talking about or if he is making some sense into it. Now, the clue lies in the June 2007 Edition and let me dished them out for you
Below are the patterns of failure, this is how your components or parts behave. John Moubray author of RCM further indicates in his book that these three failures mostly occur in combination by studying parts behavior and led to what we call the 6 failure pattern, But eventually those 3 patterns of failure (bathtub curve) can be seen as existing in TPM books, Statistical books and Weibull Distribution.
PATTERNS OF FAILURE (HOW FAILURE OCCURS)
Infant Mortality Failures - These are failures that occur at the beginning of its life. Others call them start-up failures, commissioning failures which are likely to occur after a major overhaul or Preventive Maintenance had been initiated
Random Failures - These are failures that can occur at any given period, and this is where our routine Preventive Maintenance will be at its weakest point, recommended task that can be used for Random failures will be Predictive Maintenance if the failure provides a warning or potential failure and that it is on the verge of process of occurring, modification or simply run it until it fails if the consequences of failure will be low and tolerable
Understanding these patterns is the key in uncovering the mystery why most industries are reactive or is it really a mystery or lack of solid understanding. But first let us define the following maintenance strategies so we can have a common understanding.
REACTIVE MAINTENANCE: A strategy which tells us that when a machine fails then maintenance simply fix it. Maintenance is done at a point when there is an actual breakdown. It occurs when repair action is taken in the event of a failure. Other terms used are breakdown maintenance, unplanned breakdowns, run to fail, run to destruction, band aid maintenance, no scheduled maintenance which simply means that when something fails we are here to fix it.
PREVENTIVE MAINTENANCE: These are maintenance activities performed on a fix operating schedule in order to extend the life of the equipment. It assumes that the condition of the machine is correlated with time which means that the part or component can be expected to operate reliably until a period of time and is expected to wear out. Other terms use are Calendar-Based, Time-Based, Schedule Discard & Schedule Overhauls and the time can be referred to as hours, days, number of strokes, running time etc.,
PREDICTIVE MAINTENANCE: These are maintenance activities geared in indicating where a piece of equipment is on its critical failure curve and predicting its useful life. This is done with the aid of non-destructive instruments. It also check the equipment for potential signs of failures. Other terms used are Condition-Based Maintenance, On-condition tasks, Reliability-Based Maintenance. Performing maintenance will be based upon the condition of the equipment and not based on time differentiating it from Preventive Maintenance.
PROACTIVE MAINTENANCE: Just the opposite of reactive maintenance. Proactive Maintenance is about analyzing why failures keep on recurring through techniques such as RCFA/RCA. Parts are modified or redesigned to lengthen the part’s lifespan. I would say that modifications, redesign, analyzing failures all belong to this category.
Ok, now we know the different maintenance strategies and how each failure occurs or failure pattern, so let’s just tie it up with basketball. Most industries I know rely too heavily on their Preventive Maintenance efforts, yet even with the best structure and software a lot of failures still occur. Why ?
Preventive Maintenance will only be applicable to age-related failures or to those whose parts have a direct relation to age itself, and when the failure is random in nature then there is no amount of Preventive Maintenance that can solve this problem, in fact this is where Preventive Maintenance will be at its weakest point. And secondly too much activities on PM most specially overhauls will increase the chances of Infant Mortality Failures to occur.
A quote from the original manuscript of Stanley Nowlan and Howard Heap on Chapter 1 page 3 states that Consequently, a maintenance policy based exclusively on operating age (he was referring to Preventive Mtce) would, no matter what the age limit have little or no effect on the failure rate.
A basketball team mainly compose of 2 guards, 2 forwards and 1 center. Now lets speculate and imagine if your first five where all center, it is like assuming that all parts will eventually wear out which is unlikely to happen since only around 15 to 20% of most components have a wear out pattern.
Imagine putting a basketball team of 5 people all guards, then it is like assuming that all parts will fail randomly, again there are still the infant mortality failures and wear out failures.
Therefore, the best maintenance strategy to adopt is not about being proactive or applying the best predictive maintenance strategy but it is about creating a balance and understanding when to use all these strategies simultaneously since every failure have their own unique pattern and every failure pattern should have their own specific maintenance task to adopt and not to mention that we must also look upon the consequences of failure itself.
Putting too much effort on your current Preventive Maintenance activities will only lead you to more failures since PM can only accommodate failures that have a wear out pattern. This is like putting 5 centers in one basketball team. Your team won’t work, they won’t blend. This is what I believe the reason why most industries are reactive, since they place all their center players in one team. They assume that their current PM will capture all kinds of failures. Eventually they are wrong in every way.
Hence by studying how a part behaves and fails, we can adopt a more appropriate and suitable maintenance task that will be more much more effective. So try to observe the parts and how they fail. Here are some of my recommendations :
If the part or component has a wear out mode and consistently survive this period and there is a direct relationship between its age and rate of wear, then the best maintenance task to adopt is to undergo a Preventive Maintenance replacement or overhaul.
When the part fails randomly, which means that the part can fail at any given period, then you have three options. First, Run to Fail for failures that have minor consequences or parts with redundancies. Second, Predictive Maintenance for random failures that have potential failures or signs that it is in the verge of failing. Lastly, Modify or Redesign when both Run to Fail and Predictive Maintenance is not applicable.
Remember that around 15 to 20% of parts will fail due to a wear out mode, and that the majority will fail randomly hence, let us not rely too much with our center players. A good basketball coach always knows when to place the right players at the right time, and a good maintenance structure is knowing when to adopt the different maintenance strategies at hand.
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RELIABILITY NEWSLETTER |
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Welcome to your Reliability Monthly Newsletter for the month of July 2007. You are receiving this email because at some point in time and for reasons that you opted to be included in our Newsletter mailing list from our web at www.rsareliability.com
Our newsletter will be sent out once a month and provide you with quality articles and resources on our most common link which is reliability and maintenance, as well as regular updates on our articles. I would like to personally invite you to visit our new website regularly and check out updates on our articles and training courses.
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My Warm Regards,
Website : www.rsareliaiblity.com Email : rollyangeles@rsareliability.com |
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RELIABILITY & MAINTENANCE CONSULTANCY FIRM
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Issue No. 3 - July 2007 |
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