Hello All,
We have an ambient reheat fan that is powered by a 1180hp motor which in turn is coupled by a single stage gearbox which in turn drives the fan to 490 rpm. This particular fan had a coil leaking water continuously into the fan on a day which just happened to be one of the coldest day of last year (a few weeks ago). It ran for a few hours before a mechanic happened to hear the fan, he said it sounded like a freight train. Needless to say the water on the blades turned to ice and caused a severe imbalance when the fan was started( this fan had not ran for a few weeks)which caused severe damage to the IB and OB bearings(center hung fan)along with other fan damage. Now the question, what kind of monitoring devices are out there that could of had possibly caught this before this catastrophic failure? This fan is shceduled on a monthly frequency vibraiton collection. But as you can see anything can happed within a month. Any suggestions are appreciated.

Thank You In Advance
Rafael

By the way Terrence, Excellent Conference last month, you are to be commended for a job well done!

Rafael,

up here in northern Canada, freezing and thawing is a common problem. In my travels, many of my customers utilize a vibration shutdown swith (red Murphy box) if online vibration monitoring is not available. However, the easiest solution might be to have the mechanic or millwright watch the unit start up. With long periods of inactivity, many fans will start to corrode, which will also give an unbalance situation. Good luck and welcome to the world of ice and snow!

Brian

Freezing fans in Texas - who would have thought!

I hope all of the "north of border" Canadian maintenance members have some good information to share.

Thanks for the nice comments about IMC-2004 - glad you were there. We have lots of room for improvement and are already planning some for IMC-2005!

We faced simiar problem at our ash silo vent fan, where the ash deposits on the fan cause imbalance especially in the humid season. This had caused damage to the impellers and foundation of the fan sevral times. Now we made two modifications which have reduced the damages significantly. Firstly, we have provided a heating jacket around the fan casing utilizng a nearby condensate return line. Secondly, we have installed vibration switch and set it up to trip the fan before the vibrations cause damage to the fan.

Thanks for all your replies, it's good to know that there is so much wisdom out there in the vibration world. Brian when you said a vibration shutdown switch, I'm assuming that it's a mechanical vibration switch. Have any idea where I can start looking for one of these switches?
Thanks in advance.
Rafael

Rafael,

the internet is the best place. Go to
www.fwmurphy.com or do a google search for vibration shutdown switches.

It looks as though they have a distributor in Texas, but their head office is Oklahoma. They make a full line of shutdown switches. These are mostly what I see in the oilfield up here.
They are a mechanical, contact style switch.

Brian:
Thanks for the info, I'm following up with a company located in Houston (2hours drive) called Metrix/Beta. They sell a fairly inexpensive electronic vibration shutdown switch that may work.
Again, thanks for all the suggestions that were made.

Regards,
Rafael

Rafael, when do you next expect ice in Texas )

Brian, In the past February has been our coldest months and normally have our share of ice, but your guess is as good as mine! Temperature changes very quickly in Texas. It can be 70°F during the day wearing t-shirts and shorts and then raining ice in the evening. The cold spell(low in the low 20's,highs around 30°F) that damaged the fan lasted for about3 days. That same weekend we had temperatures close to 70°F which lasted for about a week. During the summer I've seen it rain on one side of the street while the on side I was standing on was sunshine, go figure! The saying around here is,if you don't like the weather in Texas today, just wait and it will change very soon.



Regards
Rafael

Rafael,

I was not aware that Texas had such extremes of cold weather. Here in Scotland we get lots of different weather too - lot's of different types of rain :O)

I have spent quite a bit of time up in the Boston area and their saying is. "If you don't like the weather wait a minute!"

Brian,
There has been times when we've had single digits temperatures with 15-20mph winds from the north! Ouch! We've been fortunate so far just to have temperatures in the 20's. If you happen to be in the states, come on down and visit Texas, but if you're driving bring a LARGE cup of coffee(El Paso is closer to California than to Dallas).

Concerning the fan in question:
A suggestion has been made to change the pillow-block ball bearings to split roller bearings on both the inboard and outboard end.

What do yall think?

How about use FMEA to identify all potential failures for this fan and weight their risk based on likelihood and consequence? From this analysis, actions for operations, technical & maintenance can be specified, which could include operator checks during start up, design changes such as online monitoring etc. TQ

Rafael ,

Was there any opinion or approach on the suggestion?

What have experience on Split bearings for fan applications been? These are supposed to handle out-of-turn vibrations better than DRSB...

quote:

Originally posted by Rafael:
Concerning the fan in question:
A suggestion has been made to change the pillow-block ball bearings to split roller bearings on both the inboard and outboard end.

What do yall think?