The pump shaft has broken; I seek expert advice on analyzing the fracture surface
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It is a long-axis vertical pump; during operation the pump shaft broke, with the break occurring at the intermediate shaft guide bearing. The fracture site is shown in the diagram. Could the cause and mechanism of this fracture be analyzed?
I hope everyone will share their opinions and conduct some analysis.
It’s best to use data for analysis – how much was the radial vibration in the previous days? How much axially? What is the temperature of the bearing housing? How does the bearing sound look (using a stethoscope)? What are the coupling alignment data? How many shims are used for the coupling clearance? Are the import and export volumes normal? Special inspection mechanisms should be established for moving equipment, with the data being recorded.
It’s probably caused by excessive load, or the shaft is stuck.
There are many reasons for shaft fracture: 1. Poor material quality; 2. Jamming; 3. Eccentricity, as one side of the cross-section is severely damaged and the fracture surface is relatively flat. When the pump suddenly jams while operating at high speed, the situation will be as shown in the image
This is especially true for fractures in the middle of the shaft, where the area is weak under stress
This post was last edited by “Please, please” on June 25, 2017, at 18:45. The fractured area seems to be worn; there’s excessive play in the bearing, resulting in significant rotor wobbling. There might be friction or collision between the rotor and the housing. The shaft broke due to tangential forces. Please check whether there are any wear marks on the housing.
Only half a turn of the pump shaft shows obvious wear marks
Give it a push, don’t let it sink. Are there anyone who specializes in fracture analysis?
Twisted off; it’s likely the middle bearing is stuck
Personally, I think it was fatigue fracture, probably caused by the bearings not being aligned; there was no plastic deformation in the vicinity. Check microscopically for streaks.