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Curran919

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Reply with quote  #1 
You may have done a double-take at that title, but that is exactly the question I am asking. I had a big discussion with my colleagues after a number of miscommunications with describing something as a failure or a part/machine as having failed. You may hear someone say, "we had a seal failure on our feedwater pumps yesterday," and be able to interpret a huge variety of severity that they could be talking about. Why do we use such a inexact word? As Olov said in his recent thread:

Quote:
Originally Posted by Oli
the bearings last 800 to at best 1000 hours before worn out, not failed but interfering with the work of the machine due to clearance increase


The technical definition of failure is any state where the machine is not performing to specification. Therefore in Oli's case, it would technically be failure, but you need to differentiate it from being a catastrophic failure, where the machine cannot be operated (within the spec or not). We have other words for this: fault, defect, flaw, deviation, noncomformity.

It is my preference to use 'failure' for catastrophic failure that immediately prevents further operation of the machine, and to use fault for minor failures where the machine/part is operating out of spec. The machine can keep operating with the fault, but risk of failure is increased, or production amount/quality is affected. There is obviously not a strong line between the two, but it at least immediately communicates severity.

Thoughts?
MarkL

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Reply with quote  #2 
Curran I class as follows, but it's merely my own understanding.
Failure- The machine is not longer in an operational condition.
Fault- This I class as something hindering operation to full capability/design capacity, but machine is still operational.
Cathastrophic failure- the machine is totalled/has landed in bits in the next county over.

I always mention the last one when trying to get my point home on more serious findings in my PdM reports.

Big Al

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Reply with quote  #3 
In John Moubray's RCM II he refers to the P-F curve with which a lot of us are familiar. The P stands for potential failure and the F stands for functional failure.

Potential Failure: identifiable physical conditions which indicate that a functional failure is about to occur or is in the process of occurring.

Functional Failure: the inability of an asset to meet a desired standard of performance.

Once the desired standard of performance is no longer achievable then technically the machine has failed. Catastrophic failure on the other hand is a whole other ball game, that none of us are fond of playing.
RGf

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Reply with quote  #4 
I rarely use the term "failure" unless the machine in question is no longer running or is in a state that it is a hazard. My favorite expression is "the machine is in a state of considerable distress". It gets management attention in the morning meeting. The prior regime wrote up everything as a failure and soon lost credibility.

 
Dan Timberlake

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Reply with quote  #5 
I feel plumb lost when the description is "noisy" bearings, "bad" bearings, or "and then I told her she told her she should have told her she was done with her and all her drama." 
RustyCas

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Reply with quote  #6 
Quote:
It is my preference to use 'failure' for catastrophic failure that immediately prevents further operation of the machine


Generally, I would agree.  As in the following write-up:  "Pump outboard bearing has failed (broke off one bearing cap bolt, and the other backed completely out). Pump bound up and the rubber coupling element was ejected; motor was still running. Replace pump."

However, consider this: "The outboard pump bearing has failed; bearing energy now exceeds 80 g’s. Recommend removal from service ASAP."  I'm pretty sure you have to call this a "failure" even though the pump was still running.

Pump Brg Fail.png 


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RustyCas

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Reply with quote  #7 
And then this one:  "Motor outboard bearing has failed. Vibration is very high due to imbalance – motor shaft is running off-center at the outboard end."

I could see the "wobble" of the motor shaft at the fan end -- probably had 0.050" clearance in the bearing.

Motor Brg Fail.png 


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RGf

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Reply with quote  #8 
Yeah-80 G's is what I would consider a failure. I'm not sure if I would want to get up close and personal with a machine running at that level. In my company they have tried to standardize the verbiage on what is a failure and the like. They have categories like watch/marginal/unacceptable but that is pretty subjective depending on the analyst and how plant management wants it reported so their really is no standard. I put quite a few machines on the watch list that others might classify as marginal or unacceptable as I believe if it is still performing it's function its still somewhat okay even with known bearing faults etc. I only have so many bullets in my belt and of course limited maintenance resources at my disposal.   

The way I approach a machine in obvious distress where I believe the machine is in danger of coming to a sudden, catastrophic stop is I don't worry about the wording in the work order until I've had Operations swap to the other machine and verified that that machine is in a good enough condition to run until the other one is repaired. Then I can get fancy in the work order/failure description.
RustyCas

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Reply with quote  #9 
Quote:
I don't worry about the wording in the work order...


Me neither.  I call someone and tell them to remove it from service ASAP if there's a spare.  I too try and get all the useful life out of run-of-the mill machines.  It really depends on the situation.  I have the luxury (?) of being the only data collector / analyst in my plants so there's not a lot of ambiguity, except what you get when you try and explain technical things to people who have little idea what you are talking about.  I normally focus on what they should "do" with a machine, but I include enough explanation to convey that I'm not just making stuff up.

When I call anything a failure, as MarkL says, there needs to be visible evidence when the machine is disassembled.  Otherwise, they'll think I'm just crying wolf.

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Sinski

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Reply with quote  #10 
Quote:
Originally Posted by RustyCas


Me neither.  I call someone and tell them to remove it from service ASAP if there's a spare.  I too try and get all the useful life out of run-of-the mill machines.  It really depends on the situation.  I have the luxury (?) of being the only data collector / analyst in my plants so there's not a lot of ambiguity, except what you get when you try and explain technical things to people who have little idea what you are talking about.  I normally focus on what they should "do" with a machine, but I include enough explanation to convey that I'm not just making stuff up.

When I call anything a failure, as MarkL says, there needs to be visible evidence when the machine is disassembled.  Otherwise, they'll think I'm just crying wolf.


I pretty much agree with this although to me if its still running it has not failed. With some of those examples before I would use the term failing.
I had one yesterday where a coupling had decided to let go on one of our machine drives. I had arrived onsite very early in the morning (4am) to do a paper machine survey, Came in early as we are having a bit of a heat wave at the moment, and the foreman reported to me a noise on one of the machine drives. I went and took some data from the drive, although pretty clear what was happening without data, and reported that the coupling was in the process of failing. Ended up shutting the machine an hour later along with a paper break to replace the coupling. Lots of coupling shim was found on the ground when the guard was removed.
electricpete

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Reply with quote  #11 

Good discussion. My two cents, not much different…

 

Like others said, we generally reserve the word “failure” for when the machine stops doing it’s job (pump stops pumping fluid for example).

 

Some of the ways we characterize our findings are in terms of vibration level (slightly elevated, elevated, very high) and/or degradation (early-stage degradation, moderate degradation, severe degradation).

 

If the machine is still running and doing it’s job (pumping), but we want to convey more concern about the severity, we would call it “imminent failure”. 

Of course that invites the $64,000 question…. “how long?”

Unfortunately I’m no longer allowed to respond with my Dirty Harry imitation: “Do ya feel lucky punk?. ... Huh? ...Do ya?”

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