Image of broken shaft in circulating water pump
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In the external circulation water pump of a refinery’s utility system, it was discovered on the morning of the 11th that the end cover at the non-connected side of the bearing housing had fallen off; upon disassembly at noon, it was found that the shaft was broken. This pump is of horizontal split-type, double-suction centrifugal design, with model 28SH60-6. Its flow rate is 4000 m3/h, head is 52 m, rotational speed is 990 rpm, shaft power is 666 kW, and motor power is 800 kW. The impeller is made of 316L material, while the shaft is made of 2Cr13 material. The images of the defects are as follows: 1. Crack on the impeller side; 2. Crack on the coupling side; 3. The rotor is broken into two pieces. Currently, there are no replacement parts available for the pump shaft. How should this situation be handled, and how can the cause of the problem be traced?
After operating intermittently for over 2 years, with three pumps in use and one as a spare, it has never been disassembled, nor any damage has been detected.
It was caused by a sudden jam in the bearing, and you can’t find any other reason for it; previously, we experienced a broken back wheel due to this very issue.
How was it possible to notice the bearing cover coming off first? Didn’t it break suddenly during operation? Did the mouth ring and things like that not get scratched? The break is at the shoulder of the shaft, with a sleeve on the outside. From an outsider’s perspective, it seems that this cross-section wasn’t formed in one go. It’s possible that there was a crack originally or at some point, which gradually led to separation.
Fracture must occur over a certain process; besides, there are so many parts on the shaft – even if it breaks, those parts can’t just fly out all at once!
The high-voltage motor is 800 kW, and the photomotor weighs nearly 6 tons.
The operating cycle is long and the bearings wear out. The balls are in contact with each other
I think the shear stress on the pump shaft cannot be withstood by the rolling bearings. Furthermore, once there is no rolling friction in a rolling bearing, the load will generate a large amount of heat; the bearing housing may shift out of place or the cage may burn up – such phenomena are highly likely to occur, and it’s hard to imagine the shaft breaking directly.