When all else fails, leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery.
The seasoned Analyst
Introduction:
Online vibration monitoring is a great tool that enables monitoring of a vast number of assets, it helps the analyst when they “can’t see the woods for trees”.
This post is to highlight that for a full assessment of an asset you don’t just sit in your air conditioned office looking at the data on the screen. You must use other technologies and inspection tools to assess the Reliability of the system, the best tool is experience and your human senses.
Background:
The SPM online system alarmed on a fan bearing. This fan has a direct drive AC motor to a fan lay shaft with two SKF/Cooper split bearings.
The onsite vibration analyst called for an inspection of the bearing due to mechanical/component looseness and an outer race defect. I was asked to confirm the diagnosis and provide further details.
Pre-Vibration Analysis:
On review of the data, and the new on demand live data, from the SPM system I concluded that the analyst was correct in the diagnosis of mechanical/component looseness and an outer race defect on the split bearing.
Figure 1 is the SPM online Velocity spectrum from the 1st September, with low overall one order and no harmonics.
Figure 2 is the SPM online Velocity spectrum on the 3rd September, and shows many running speed harmonics indicating a component/mechanical looseness.
Inspection :
Before I issued my comments I decided to “Leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery”. Within seconds I spotted the issues and using my personal Motion Amplification tool, my finger! I felt and confirmed what my eyes were seeing.
Image 1 is of the drive end (Motor side) split bearing, all good.
Image 2 is of the fan NDE bearing (Fan side). The top cap retaining bolts were coming loose!
Corrective Actions:
This was reported immediately to the on site maintenance team. Maintenance re-secured and torqued the bearing top cap bolts. It was found that both bolts were loose!
Post Vibration Analysis:
Figure 3 is the SPM online Velocity spectrum after the corrective actions, 3rd September. This shows a large reduction in the 1 order harmonics, confirming the loose bolts were the cause of the harmonics. It was also noticed that there were still some higher frequency data evident that was not there prior to the 3rd September.
Further analysis of the SPM HD Envelope spectrum displayed a clear defect signal for the outer raceway. This is a split bearing so you would expect to see some bearing signal but the fan end is a lot higher. This is not surprising giving that the fan end bearing was in operation with a loose top bearing cap!
The data below compares the drive end (motor side) Figure 4 and non-drive end (fan side) Figure 5 SPM HD Envelope spectrum. This confirming that the fan end bearing signal is a lot higher.
Summary:
This highlights that there is a place for an online monitoring system in some aplications.
In addition to preventing a catastrophic failure of the fan and this having a effect to the profitability of the site, this prevented what could have been a very dangerous safety incident with a fan coming loose at full speed.
For a full assessment of the system please leave the air conditioning, and go examine the operating equipment. Go look, touch, feel, smell and listen to the machinery. Don’t site and rely on one form of data to make a decision that will affect the reliability and probability of the system.
A profitable plant is reliable, safe and a cost-effectively maintained plant.
The Seasoned Analyst