Root Cause Analysis (RCA): Too poor antifriction bearings lives caused machine changeovers posed upsets / outages.
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 two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.
An always running turbine driven 800 KW 3000 RPM BFWP and its rarely run motor driven auto-start standby feeds 5 Nos. boilers-hence highly critical as waste heat boilers shutdown is not easy in case of failed boiler feed water (BFW) supplies
Yellow zone shock pulse meter readings within two months service and consequent motor driven a daylong run and the external very unreliable power supply threatened the entire fertilizer plant shutdown (SD) for long periods.
Boiler | P | SPR | |
Process Waste Heat Boiler E-101 | 40 | 100 | |
Process Waste Heat Boiler G-101 | 40 | 100 | |
Process Waste Heat Boiler E-104 | 10 | 100 | |
2 Nos. oil fired boilers | 40 | 50 | |
Total 5 Nos. |
P-pressure kg/Cm2; SPR-Steam Production Rate T/H
The author, read to the maintenance group from bearing vendors catalogs, “Designers select AFBs of 50,000 hours (≈6.5 years) service lives for 24×365 service machines, and even 200,000 hours (≈27 years) service lives for 24×365 highly critical machines e.g.
Boiler Feed Water Pumps (BFWP). He exhorted the ‘experts’ to Root Cause Analyze the problems and take steps to realize at least 50% of possible lives.
The ‘experts’ accustomed to 10‑yearlong frequent AFB changes and of spurious bearings mindset ridiculed the author behind his back as impractical theoretician. In the absence of response, the author Root Cause analyzed the critical BFWP poor AFB lives:
The pump manual specifies New Departure Co USA L1A suffix AFB. The ‘experts’ said suffix numbers are unimportant and equivalent basic number SKF AFBs they substitute are sufficient.
The author read to the group from bearing catalogs that suffix numbers too are important as they specify the selected bearing’s special features to meet specific operational requirements!
Local SKF office forwarded to the author SKF Sweden office advice: ND L1A suffix means C3 clearance – higher than normal clearance – and nylon cage AFBs because of the two reasons given below:
Implemented RCA solution benefits are:
Delving further the author found the following:
The primary reformer a critical process’s 750 RPM FD fans grease lubricated AFBs too lasted 6 Months only. Changing to oil lube increased the lives to 9-Months.
Fit up and alignment errors were absent. Hence, the author concluding selected bearings insufficient load capacity, substituted a cylindrical roller bearing of 4 times the dynamic loading capacity modifying the pedestals to accept the new plummer blocks. The bearings lasted and lasted
Benefits of the modification are:
This 4600 RPM 20 kW machine runs for 2 hours in every 8-hr shift. Tired of the few days AFB lives the plant engineer retired the machine, and hose connected plant air supply for instrument air dryer alumina gel drying.
The author came to know of this unauthorized modification. He studied and found bearing fit up and other problems are absent. He substituted 4 times higher dynamic load capacity bearings with necessary pedestal changes. The problems vanished
Author: S. Raghava Chari
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