Analysis of the causes of shaft fracture in circulating water pumps!
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Brief overview of the pump shaft: The pump has a power rating of 450 KW. Wear was detected on this pump shaft during a planned inspection in December 2015, after which a new shaft was installed; it has been in use ever since. In April 2017, the vibration of the pump bearing increased and the temperature rose; disassembly for inspection was planned. Upon disassembly, it was found that the pump shaft had broken at the junction with the impeller (shaft journal diameter: 95 mm). The relevant images are shown below; the cross-section appears dirty, but it is actually smooth – although it is not a perfect flat surface ； My analysis: 1. This cross-section is very smooth, which is consistent with the characteristics of fatigue fracture; however, the pump has not been in operation for long, and neither the shaft keyways nor the keys are worn out. Even after breaking, the pump continued to rotate thanks to the connection provided by the keys ； 2. Defects in the pump shaft manufacturing; this pump shaft was also purchased under emergency circumstances, and the forging process may not have been carried out thoroughly. Please point out any mistakes in the above analysis at your earliest convenience. Thank you all.
The shaft broke before the impeller did; it must be a manufacturing defect – the heat treatment was not done properly
Hello, may I ask what kind of heat treatment is required for this type of shaft? Thank you
I think on the contrary, it is the heat treatment that causes the fracture, rather than twisting!
I also think it’s caused by heat treatment issues; in our company, there was a case where the shaft of a 315KW circulation pump broke, due to wear on the shaft, and it was repaired by welding. . .
It is recommended to check whether the foundation bolts of the equipment are loose; the key point to note here is whether the bolts hold the equipment firmly in place. Such things have happened: the nuts were tightened, but the equipment couldn’t be secured due to threading issues. Here, it is necessary to loosen the nut first and then secure it; while securing it, check whether the bolt twists as well. If it does twist, it means the device has not been properly secured. If any abnormalities are detected during securing, the device must be realigned and centered again. Shaft breakage incidents caused by foundation bolts are often overlooked. For reference.
Our company has encountered the same problem with pump power of 450 KW for circulating water pumps; the cause was a lack of oil in the pump bearing chamber, as no oil was added in time, which led to an increase in the temperature of the pump shaft and bearings and ultimately to their failure.
The shaft ends connecting the impeller are all fitted with chip clearance grooves; this area is subject to the least shear force. It is necessary to check whether the pump may be operating in reverse, or whether insufficient precision in the threading of the impeller cover could lead to oscillations of the impeller caused by air erosion, thereby generating shear force.
His should be a double-suction pump supported at both ends!