Power of MCA
The motor at a coal-fired steam plant was experiencing increased vibration levels. We used motor circuit analysis to find the cause.
The Allied Reliability team was able to determine why a company’s grinding mill was experiencing repeated bearing failures through a Root Cause Analysis (RCA), a systematic methodology used to eliminate chronic problems that affect an organization.
The asset is a vertically-mounted, belt driven grinding mill, as shown in Figure 1. The drive spindle has three (3) bearings: two (2) cylindrical roller bearings and one (1) ball bearing. The mill is being belt driven by a 100 hp, two-pole motor. The mill normally operates at 3,150 rpm.
Legend
The mill rotor bearings, which are mounted in the steel housing, are two (2) cylindrical roller bearings, NU 316 ECM/C3, and one (1) grooved ball bearing, SKF 6316 C3. The bearings have failed several times over a period of two (2) years. Before this time, the mill had no recorded bearing failures (as confirmed by the CMMS).
In 2007, the vibration spectra began displaying excessive looseness. A work order was submitted by the vibration analyst, and the bearing assembly was rebuilt and reinstalled by on-site mechanics. (See Figure 2.)
In September 2009, the vibration data was again showing bearing defects. At this time, the old bearing housing, shaft, bearings, and seals were sent to a local precision mechanical shop for assembly. The on-site mechanics performed the replacement of the bearing assembly, rotor, sheaves, belts, and motor.
In February 2010, the bearings failed again, this time with very little notice. A new bearing assembly was purchased from the manufacturer at this time. This assembly was again installed by the on-site mechanics. (See Figure 5.)
In November 2010, the bearings failed yet again. (See Figure 6.)
Note in the photographs in the Supporting Data section that all of the ball bearings (with the exception of the first one) failed in the axial plane.
All of the photos in this report were taken, cataloged, and documented by the Allied Reliability analyst working at this location.
Due to the repeated failures, this asset triggered a Root Cause Analysis. The investigation eventually revealed the cause of the failures. During the investigation, we verified many different issues. Some of the most important issues were as follows:
The bearing supplier's engineering consultants suggested the plant return to the old bearing style. In addition to the poor application of this new style of bearing, the lubrication was not entering the bearing due to the style of the cage (the old bearing was unshielded). (See Figure 7).
We were able to correct the issue by performing several actions:
Root Cause Analysis Cost Information
Goal | Impact to the Goals | Costs (USD) |
Production | 120,000 lbs | $40,000.00 |
Maintenance | 2,500 parts and hours | $2,500.00 |
Subtotal | $42,500.00 | |
Frequency (Number of Times per Year) 3 | 3 | |
Annual Total | $127,500.00 |
The importance of documenting all of the data for any critical asset cannot be overstated. While the difference in ball bearings is obvious in all of the photos in this report, without the past failure data being catalogued and stored by the previous analyst, this bearing change out may have continued to go unnoticed.
The analyst who was working at the facility had only been at that location approximately six months; however, due to the proper documentation by the previous analyst, he was able to do his job and compare the current data with the old data and find the change that started this chain of failures. It was while looking through photos of past failures that we first noticed the differences in the bearings.
The motor at a coal-fired steam plant was experiencing increased vibration levels. We used motor circuit analysis to find the cause.
Advanced vibration analysis was performed on the blower and supporting base structure to determine the root cause of the elevated vibration levels that were affecting this equipment.
A health treatment facility noticed an elevated temperature with a fan assembly breaker. We used multiple technologies to find more faults with increased certainty.
713-682-3651
10344 Sam Houston Park Drive
Suite 110, Houston, TX 77064