Page 2 of 3
In November 2011, the plant Operations team observed a spike in DE and NDE bearing housing vibration, and a spike in DE bearing temperature. The DE bearing temperature increased suddenly from 120°F to 268°F. The DE bearing housing vibration increased from 0.16 to 0.27 IPS while the NDE vibration increased from 0.24 IPS to 0.4 IPS. The temperature spike lasted about 18 minutes, after which the temperature dropped to 92°F. The vibration spikes lasted 6 minutes, after which the DE vibration fell back to 0.16 IPS and the NDE dropped back to 0.22 IPS. A review of past operating data showed a similar spike in DE bearing temperature in September 2011, but there were no associated vibration spikes. The spikes in both temperature and vibration in November 2011 indicated possible bearing issues. A vibration analysis was performed, which showed that the vibrations were at a frequency corresponding to running speed.
A planned plant outage was scheduled for January 2012 and it was decided to inspect both the DE and NDE bearings. The DE and NDE bearing temperatures and
The bearing inspections revealed significant damage to one side of the DE sleeve bearing. Both oiler rings were worn through and the shaft journal was severely scored, but the shaft was straight (0.001? TIR). The thrust bearings had also failed, but there was no damage to the thrust collar. See pictures in Figures 3 and 4. The motor centerline was also found to be 0.050? lower than the fan.
The NDE bearing also was found in good condition. See Figure 5.
The rotor was removed from the fan housing. Both sides of the DE shaft journal were machined down, spray coated and machined to design dimensions. The rotor was then dynamically balanced.
The entire DE bearing housing assembly also was replaced. This included the housing, bearing liners, thrust plates and oil rings. After the outage, the bearing temperatures have not changed, but both the DE and NDE vibration levels dropped to under 0.02 IPS.
Heinz Bloch is a renowned rotating machinery consultant and author. On Feb. 29, 2012, he held a webinar entitled, “Lubrication and Failure Avoidance.” The webinar was sponsored by Hydrocarbon Processing and readers are encouraged to listen to it.
In this webinar, Bloch stated the following, “… in all equipment styles and machine configurations, machine types running or machines ever built: every problem fits in one or more of these 7 cause categories. Thus, a lubrication defect is always traceable to:
- Faulty design
- Material defects
- Processing and manufacturing defects
- Assembly or installation defects
- Off-design or unintended service conditions
- Maintenance deficiencies (neglect, procedures)
- Improper operation.”
The fan that is the subject of this article had been in service for 17 years with no significant issues.