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centrifugal pump casing failure

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xgiorg

Industrial
Jun 10, 2008
37
Hi!

The last week we had a centrifugal water pump failure. The recirculation pump allows 10bar and 120C, bought on 2009. The system works with water at 4bar and 90C. After stopping the first pump, the reserve pump didn't started. After an hour they started and all was ok, but suddenly, after 1 minute more or less the pump burst. The system have security valves rated to 10bar, then it is impossible to have overpressure. I think the problem can be it exist an economizer before the pump, and during the stop water reached 150C without vaporizing. Does a 20 to 150C temperature transition can brake a pump? Also I checked the case wall thickness in different places and I found 5,5mm to 12mm variation. Is this allowable? We're I can find more info about it? I attach some pictures, thank you for your help.
 
 http://files.engineering.com/getfile.aspx?folder=d0dd9dde-aa3c-4fd5-83dd-9474e4f34380&file=DSC_0020.JPG
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Yep. The 150C is what got you. Your Cast Iron fitted pump is not made for that temperature; there are so many things that go wrong. Your pump looks like it just cracked the case from excessive heat; 150C should have a carbon steel or SS centerline mounted casing.

One thing to think about: pumps made for higher temperatures have their support mount locations centered along the shaft centerline axis. That way, the thermal growth caused by elevated temperature moves symetrically away from the shaft. With a foot mounted casing, such as yours, the thermal expansion is busy misaligning everything.

Sounds like you just economized yourself into buying another pump.
 
The problem is that before the failure, the economizer was located after the pump. Then if some temperature increase occurs, the water was cooled in the line before reaching the pump. I don't know why they changed it, because they didn't verify the allowable temperature in the pump.
I read that theorically a PN10 din 24255 can work till 160C, but the specification say 120C for GG25 cast and I know is their fault.
Now I'm interested in knowing if the cause of the failure is thermal expansion or vaporisation occurs inside the pump, just to understand what happens. Someone knows if the thickness wall variation is allowable?
Thank you a lot for your help, I don't know too much about pump failures
 
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