Hello all,
Can anyone tell me the possible root cause of pump shaft broken? Broken position is over packing follower about 2-3 cm. and shaft surface have been repaired by thermal spraying.
Thank,
weerasak.

This message has been edited. Last edited by: Weerasak W.,

Shaft_1.JPG (74 KB, 115 downloads)

picture #2
Pump detail: Vertical, Centrifugal mix flow, tall about 7 m., Shaft dia about 1 1/2 inch., 3 shafts and 1 impeller shaft.

Shaft_2.JPG (71 KB, 94 downloads)

What is the pumping fluid? Upthrust may be one reason during pump starting. Corrosion. Is it possible there? Reduction in diameter due to rubbing with gland packing if sleeve is not there.

This pump used with raw water. When we diaassembly shaft not lock. Reduction in diameter of shaft is slightly, i think not more than 5%

Hi,

Since you have mention that it was repaired by metal spray, could you check if is have given time to cool down by its self or otherwise if it was force to cool down by dipping into water or oil it than there is a possibility for the metal to be britle or might create a so call hair line cracks in a metal.

This happen is some machine shops to speed up the work.

Where does the raw water come from? River? Lake? Does it pull from a pit or straight out of the river or lake?

1.) I would say your repair job was inadequate and; 2.) your alignment was terrible.

I've worked on a number of these: here's a paper on one............ if a pw is required use pdmsam

AlnBalAgitator.doc (29 KB, 64 downloads) 'em tators - alignment

The fracture surface shows evidence of rotational bending fatigue with multiple origins around the circumference. Fatigue covers roughly 60-80% of the cross section, indicating that there wasn't a whole lot of bending forces, but enough to fatigue crack the cross section.

The picture isn't color-corrected, but it doesn't appear that corrosion played any significant role in this fracture.

Thanks all of comments.

Kestas,
I agree with your comment but why i am not find the beach mark? and why the final rupture not appear close to center of surface?
I taked a photo after broken about 2 weeks.

Best regards,
Weerasak W.

P.S. I am not fluent in english, sorry if I use no good.

Beach marks can all but disappear if the amplitude of cyclic loading is even throughout the fracture process. But the fatigue striations will remain visible under SEM examination. I do see some evidence of striations at the lower right of the first picture (Shaft 1.jpg). Beach marks presented in text books usually show the appearance of fatigue with a single point initiation. This shaft has multiple origins around the circumference. Once the fracture planes join together, the fracture front will take on a circumferential character.

It is also typically rare to find final shaft rupture at the very center after rotational bending fatigue. This is because the amplitude of stress is rarely perfectly even for the entire 360° circumference of rotation. It is these small details in the application of bending and surface tensile stresses that give the unique character to each shaft fracture.

K. Smalinskas