Plant Operations, Maintenance, and Troubleshooting
This is the domain of judgement: safe start-up and shutdown, condition-based maintenance, and diagnosing a fault from evidence rather than guesswork. Items often present a symptom set - vibration signature, tube failure appearance, an operating trend - and ask for the most probable cause or the correct next action.
Operations
- Start-up: prove interlocks, purge the furnace, warm up at the manufacturer's rate. Drum differential temperature limits (commonly around 50 K top to bottom) exist to control thermal stress.
- Shutdown: cool at a controlled rate and never dump a hot drum. Select wet or dry lay-up according to duration and freezing risk.
- Logs, rounds and trend review remain the backbone; a slow trend in bearing temperature or air heater differential finds faults earlier than any alarm.
Maintenance
- Preventive, predictive and corrective work. Condition monitoring - vibration, oil analysis, thermography, ultrasound - catches bearing wear, misalignment and lubricant breakdown before failure.
- Vibration: 1x running speed suggests imbalance; 2x suggests misalignment; high-frequency broadband suggests bearing defect; sub-synchronous 0.4-0.5x suggests oil whirl. Use the spectrum, not just overall amplitude.
- Root cause analysis: five whys and fishbone diagrams, aimed at the system that allowed the failure, not the individual who happened to be present.
Troubleshooting
- Tube failures: thin-edged wide rupture = short-term overheat (low water, flame impingement); thick-lipped = long-term overheat from scale or steam blanketing; black magnetite pitting = oxygen corrosion; gouging under deposits = high pH.
- Water hammer: fast valve closure, condensate in steam lines, or flash steam. Correct with trapping, drainage and slow valve travel.
- Vibration after a bearing change: check alignment and soft foot before touching the rotor.
Worked example
A motor-driven fan shows overall vibration of 0.15 in/s, dominated by 1x running speed, rising after a motor rewind. Dominant 1x with little 2x points to unbalance or a bent shaft: check shaft runout and coupling alignment first, then balance the rotor. If 2x dominated instead, misalignment would be the first suspect and shimming the feet - not balancing - would be the correct repair.
Traps
- Replacing bearings repeatedly without examining the vibration spectrum.
- Using wet lay-up in a location that will freeze.
- Adjusting a safety valve to stop nuisance lifting instead of finding the control or setpoint problem behind it.
- Bypassing a trip to keep running without a documented management-of-change decision.