ArticleVertical Sulfur Pump
by Jeremiah S. Gerard
This brief paper gives an account of how vibration analysis was used to detect a bearing fault in a vertical pump. As the bearing condition worsened, the pattern in the vibration data changed from the presence of defect frequencies to signs of excessive clearance or looseness within the machine. Due to the persistence of the vibration analyst, a complete failure of the machine was avoided.
“A vertical pump at a sulfur recovery unit was pulled out for replacement of bearings due to abnormal noise coming from the pump. Thrust and radial bearings were replaced, and the pump was put back into service. Operations complained that the same abnormal noise was coming from the bearing housing area of the pump. This area is close to the motor, so that it was difficult to identify the source of the noise. A vibration specialist was contacted to identify the problem. The specialist took vibration data and confirmed that the abnormal noise was coming from the upper bearing housing of the pump. He was also picking up BPFO vibration at 5.24 times operating speed with a high first order component. The data indicated excessive clearance between the outer diameter of the bearing and the inner diameter of the bearing housing (Figure 1).
The maintenance department was informed of the problem, but they insisted that the bearings had just recently been changed and that it was an electrical fault. Electrical personnel finally uncoupled the motor and requested that the vibration specialist take vibration readings at free-load condition. Vibration levels were normal, and there was no abnormal noise.
The mechanics were unhappy with the results reported by the vibration specialist and insisted that they would not remove the pump again. The coupling was reinstalled, and the equipment was returned to operation. The specialist was told to monitor the condition of the pump. Within a short time, a different pattern was observed in the spectrum at all the points for motor and pump (Figure 2).
The specialist saw an increase in vibration levels at operating speed that indicated motor unbalance as well as a drastic drop in vibration levels for the pump. The BPFO at 5.240 times operating speed disappeared from the spectrum (Figure 3). Instead, operating speed and a number of orders indicated looseness. It was on a Friday evening that the engineers from maintenance and operations were informed that something was wrong. The pump was in operation until Monday before it was shut down and pulled out for inspection.
Operations stopped the pump and maintenance pulled it out, took it back to the workshop, and dismantled it. When the specialist and engineers examined the pump, maintenance showed them the new upper thrust bearing and reported that nothing was wrong. However, when the specialist tried to install the bearings into the housing, the bearings could slide in and out without any interference.”
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