Root Cause Analysis (RCA): Poorly engineered, built & often failing plant Air Comp drives made 100% reliable very economically.
Article Type: | Root Cause Analysis (RCA) |
Category: | Mechanical |
Equipment Type: | Miscellaneous Rotating Machine Problems |
Author: | S. Raghava Chari |
Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of one or two decades ago. These articles will help you to improve your troubleshooting skills and knowledge.
The author was aware of the mechanical crew struggling with the jackshaft drive coupled to the plant air compressor when he was Instrument Engineer.
On assuming the position of Instrument, Electrical & workshop Root Cause Analyzed and learned the following:
1. Two additional plant air compressors were necessary because:
2. Budget constraints permitted buying compressors only
3. Undaunted the maintenance manager though an electrical engineer overlooked the poor efficiency and consequent exorbitant electricity bills used two Nos. surplus 3.3 kV 450 kW 1500 RPM Journal Bearing Motors and jackshaft coupled them to the 250 Kw compressors (fig 1) as JB motors unsuit pulley on motor belt drives (fig 2).
4. The mechanical crew who completed the installation could not provide the very essential belt tensioning device to move the motor as necessary to get correct belt tension – the essential for long belt lives
5. In addition, because of the shop made motor & between plummer block jackshaft mounting base and other poor workmanship all over the motor to jackshaft alignment drifted often and damaged the motor bearings
6. The too often motor bearings and belts changes and the long time necessary for belt change and jackshaft to motor alignment reduced the drive availability to 50%.
7. The compressors deficiencies worsened the situation
8. Hence the much-needed plant air compressors’ availabilities were around 30% only. Hence the sandblast air costs paid to the contractors did not reduce significantly.
The author reviewed the serving HT motors and implemented the below-given solutions:
Below given are motor shifts savings:
Motor Shift Savings | Motor 450 KW | Motor 300 KW |
Efficiency at 250 kW load | 0.85 | 0.94 |
Yearly Power cost = 8000*250*5/E | 11764706 | 10638298 |
150 belt set change / yr @ 200 /set for 450 kW motor and 2 for 300 kW motor | 30000.00 | 400.00 |
Crew overtime | 100000.00 | 20000.00 |
Other miscellaneous costs | 50000.00 | 10000.00 |
Yearly Ownership costs | 11944705.88 | 10668697.87 |
Yearly savings from motor shifts Say 1.28 million | 1276008.01 |
RCA Solution Benefits are”
Author: S. Raghava Chari
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