Why must feedwater not be added to a boiler whose heating surfaces have been overheated by low water?
- The feed pump may be damaged by the hot boiler
- The boiler water treatment would be diluted
- The gauge glass would show a false high level
- The metal may be shocked and the water flash to steam
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D. The metal may be shocked and the water flash to steam
Red-hot steel that is suddenly quenched contracts violently and may crack or rupture, and the water flashing on the hot surface produces a surge of steam. Both can turn an overheating incident into an explosion.
Reference: Boiler emergencies: low water
When a cold steam boiler is being started, how long is the boiler vent left open?
- Until the burner lights for the first time
- Until the boiler reaches working pressure
- Until the main stop valve is fully open
- Until steam flows steadily from the vent
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D. Until steam flows steadily from the vent
The vent lets air out as the water heats. It is closed once steam is issuing strongly, typically at 10 to 15 psi, which shows the air has been pushed out. Closing it at light-off traps air, which causes corrosion and a false pressure reading.
Reference: Boiler operation: cold start-up
Why is a cold boiler brought up to pressure slowly?
- So the feedwater has time to deaerate
- So the fuel has time to reach the burner
- So the metal and refractory expand evenly
- So the safety valve has time to warm up fully
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C. So the metal and refractory expand evenly
Heating too fast makes some parts expand before others, which strains tube joints and seams and cracks refractory. A gradual warm-up at low fire keeps temperatures even throughout the boiler.
Reference: Boiler operation: cold start-up