Cooling tower Fan catastrophic failure

Hello everyone

Has anyone experienced a breakdown of a cooling tower ID fan where the fan blades (FRP), the drive shaft (metal) are broken in to pieces. where the vibration was very less (monitored by MCT) and 150 Kw driving motor also having less vibration.

see the attached picsIMG_5271IMG_5272

 

Thanks Akhil Rathore Great India

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Original Post

"where the vibration was very less (monitored by MCT)" What is MCT?

I did work on cooling tower fan where 3 FRP were thrown to ground and broken drive shaft was laying on the fan deck! The permanent vibration monitor was a Murphy Switch, and did not detect high vibration or cause shutdown. Another case of a useless vibration monitor!

Stay safe my friend,

Walt

Cooling towers are usually not monitored well, and I echo Walt's comment wondering what is "MCT".

One part of the monitoring problem is the initial failure often occurs with minimal warning due to the monitoring (shut down switches, scanning systems, etc.)  Once the initial mode of failure occurs, which frequently is a loss of a blade, then secondary and very extensive damage occurs.  All this can occur in a matter of seconds. 

Some things can't be predicted by vibration monitoring. For example bolt failure (crack), worn material, wrong assembly, welding failure, unexpected events (hammer falling down the tower etc.), operator mistakes and many others. That is why I tell to every customer, vibration monitoring won't prevent every single failure.

I agree with Becar, but my comment was referring to poor choice of vibration sensor/monitor and poor alarm setting (high to avoid false positive). Another aspect to a significant machine crash is the sequence of events that cause a cascade of individual component failures. We don't know if one blade broke first followed by other blades and then drive shaft or perhaps the drive shaft first followed by the blades.

Walt

SKF Machine Condition Transmitters (MCT) Series 500 are 4-20 mA Transmitters

with 2 accelerometers stud mounted one at GB input and one at output

 

Using this MCT device I collect the velocity and gE for the GB.

@Walt Strong

The sequence of events is never easy to identify.

 

I wonder at least some indication should be there in vibrations, whatever may be the fault.

Has anyone ever concluded on such failure, what happened and when?

 

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I've used permanently mounted accelerometers on the gearbox with some success to predict cooling tower problems by taking readings manually as part of a quarterly route.  In my opinion by manually taking the readings and analyzing the data you can pick up slight variances that may be missed by a vibration monitoring tool.

In my case the gearbox was very low on oil and gear mesh frequencies were recorded and the unit was shutdown before failure.  As others has said, not all failures can be predicted.

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