Shaft Centrifugal Pump failed by torsion or fatigue??
Shaft Centrifugal Pump failed by torsion or fatigue??
(OP)
Dear All,
I'm new here, i've got a problem with this stuff. Anyone care to look at this failed shaft?
It was a centrifugal pump with double suction enclosed type impeller and shaft supported with plane bearing on both ends
I'd like to know if it is torsion or fatigue or even something else that might cause it to break like this?
Material : A276 316L
Fluids service : MDEA Semi-Lean Solution
RPM : 2980
Suction Pressure (Max/Rate) : 9.0/3.8 kg/cm2G
Discharge Pressure : 36.4 kg/cm2G
Thanks !
I'm new here, i've got a problem with this stuff. Anyone care to look at this failed shaft?
It was a centrifugal pump with double suction enclosed type impeller and shaft supported with plane bearing on both ends
I'd like to know if it is torsion or fatigue or even something else that might cause it to break like this?
Material : A276 316L
Fluids service : MDEA Semi-Lean Solution
RPM : 2980
Suction Pressure (Max/Rate) : 9.0/3.8 kg/cm2G
Discharge Pressure : 36.4 kg/cm2G
Thanks !





RE: Shaft Centrifugal Pump failed by torsion or fatigue??
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
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P.E. Metallurgy, Plymouth Tube
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
But i think its not overload, but from torsional fatigue because final fracture was smaller than total area of the shaft. It means stress which applied on the shaft was below the UTS, isn't??
Besides, after i look at microstructure there was many presence of twinning grain, is there any relation between twinning grain and torsional stress (plastic deformation) ??
Could you help me again??
Thanks for your kindness
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
Is there a step in the shaft where it broke? The stress concentration at the step would really accelerate fatigue at that location.
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P.E. Metallurgy, Plymouth Tube
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
So,torsional stress doesnt have effect to twinning grain??
Im suspicious about one thing, is it possible that microstructure like this because of heating while operation??
because recently i just know that treatment was conducted on the impeller . But from hardness test, there are no different value on center shaft and its surface.
Thank for your attention
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
https://www.ksb.com/blob/189738/7fec819715ee3d7ea9...
- If Direct coupled, type of coupling ?
- Belt driven?
- Service life and repair history?
- How many of these pumps do you have?
I believe shaft features like grooves or keys can modify the "torsion = 45 degrees " rule sometimes.
Fig 3.3 page 14 here -
http://www.rexnord.com/ContentItems/TechLibrary/Do...,
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
If they heated the impeller they could have caused other problems in the structure.
Andy stress relief would make that section softer, and it would have lower fatigue strength.
If they got it hot enough they could have sensitized it, and this would have much lower ductility and lower fatigue strength.
Were there valves in this system that were opening and closing frequently? Pressure pulsations would greatly accelerate fatigue.
Was the impeller well balanced?
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P.E. Metallurgy, Plymouth Tube
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
That said, I find it interesting that the fatigue at face value appears to initiate in the interior of the shaft and then propagate mostly to the left as if it were under unidirectional bending. Final fracture occurred to the right shortly after the crack reached the OD surface on the left. I would be very focused on why this appears so, especially since most fatigue cracks are expected in this environment to initiate on the surface.
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
Looks to me like the main fatigue crack started at left, and later a sympathetic fatigue crack started at the right side.
The morphology suggests a shaft straightness and/or alignment problem, again unsurprising for a shaft.
Enquire if the equipment was recently disassembled.
mrfailure, I keep a photocopy of the handy dandy ASM graphic aid taped to my office wall
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"
RE: Shaft Centrifugal Pump failed by torsion or fatigue??
http://www.sciencedirect.com/science/article/pii/0...
Maui
RE: Shaft Centrifugal Pump failed by torsion or fatigue??