Boiler Operation, Startup, and Shutdown Procedures
What this domain tests
This domain tests sequence and judgement: the order of steps for a cold start, a hot restart, paralleling with a header, and a controlled shutdown. Items frequently present a sequence and ask what comes next, or what would happen if a step were skipped.
Startup sequence essentials
- Confirm the boiler is filled to the proper level with treated water, all manholes and handholes are closed, vents are open, and the fuel train has been leak-tested.
- Pre-purge the furnace and gas passages before every light-off - normally at least four air changes - with the burner off and the fan running. Never light off a hot furnace that has not been purged.
- Establish the pilot, prove the flame with the scanner, then open the main fuel valve. If the main flame is not proven within the flame-failure response time, the safety shutoff valves must close.
- Warm up slowly on low fire, keeping the drum level visible at all times. Blow the gauge glass down during warm-up to confirm it is not plugged.
- Warm steam headers by cracking the stop valve with drains open, then open slowly to avoid water hammer.
Paralleling and shutdown
- Bring the incoming boiler slightly below header pressure, open the equalizing line, then open the main steam stop slowly while watching level and pressure.
- Shut down by reducing to low fire, purging, closing the fuel valves, then stopping the fan. Do not drop a boiler from high fire - the sudden contraction can damage tube seats and refractory.
Worked example
A cold boiler is at 60 psig and must go on a 100 psig header. Steps and reasoning: (1) verify the drum level and gauge glass; (2) raise pressure slowly to just under header pressure - paralleling above header pressure forces steam backward and can trip a check valve; (3) open the equalizing line so pressure equalizes without steam flow; (4) open the main stop slowly, watching for water hammer caused by condensed steam in a cold line; (5) once the boiler is carrying load, close the drains.
Traps that cost marks
- Skipping the purge after a flame failure; unburned fuel in a hot furnace is an explosion hazard.
- Opening the main steam stop wide and fast, which causes carryover and water hammer.
- Leaving superheater drains open after steam flow is established.
- Shutting down from high fire, or draining a hot boiler.