Boiler Shutdown Procedure

Planned Shutdown Sequence

1. Reduce firing rate gradually to low fire. This allows the boiler to cool slowly.
2. Switch the burner to manual control and further reduce firing rate.
3. When steam demand allows, close the main steam stop valve. The non-return valve will prevent backflow from the header.
4. Turn off the burner. Allow the combustion fan to run for the post-purge cycle to clear unburned fuel.
5. Close fuel supply valves. Verify gas tightness at the gas train.
6. Allow the boiler to cool naturally. Do not force-cool with cold water or open doors. Allow at least 4 to 8 hours (longer for large boilers) before opening access doors.
7. When pressure drops to 0.5 bar, open the vent valve to prevent vacuum formation as steam condenses.
8. When pressure reaches 0 bar and temperature drops below 90 degrees C, the boiler is safe to open for inspection.

Short-Term Shutdown (Hours to Days)

• Maintain water level: Keep the boiler at normal water level. Check daily.
• Maintain pressure: If possible, keep the boiler at low pressure to prevent air ingress. If depressurised, fill completely to minimise air space.
• Close vents and drains: All valves should be closed to prevent air entering and causing corrosion.
• Consider nitrogen blanketing: For longer shutdowns, introduce nitrogen into the steam space to displace oxygen and prevent corrosion.

Long-Term Shutdown (Weeks to Months)

• Wet layup: Fill the boiler completely with deaerated, chemically treated water (with excess sulphite or hydrazine for oxygen scavenging). Maintain a slight nitrogen blanket above the water. Suitable for shutdowns of weeks to months.
• Dry layup: Drain the boiler completely, dry all surfaces with warm air, and place desiccant (silica gel or quicklime) inside. Seal all openings. Suitable for long-term shutdowns. Inspect desiccant monthly and replace when saturated.
• External protection: Apply corrosion inhibitor to burner and controls. Cover the stack to prevent rain entry. Maintain boiler room heating above 10 degrees C to prevent freezing.

Emergency Shutdown

Emergency shutdown is triggered by: low water level (primary low-water cutoff), high pressure (safety valve), flame failure, fuel leak, or other safety-critical conditions. The procedure is: cut fuel supply immediately, close the main steam stop valve, do NOT add cold water to a hot boiler (thermal shock), and allow natural cooling before inspection.

If the boiler has lost water (low water alarm), never feed water into it while it is hot. The thermal shock can cause immediate tube failure or a steam explosion. Allow the boiler to cool completely before adding water.