Auxiliary Boiler Low Water Level Alarm
You are the second engineer on a 25-year-old product tanker. The auxiliary boiler supplies steam for cargo heating and fuel oil heating. At 0600 the low water level alarm sounds and the burner trips. The boiler is a vertical cylindrical type with a gauge glass, two independent low water level switches, and a feedwater pump controlled by a level controller. The cargo is a heated parcel of heavy fuel oil requiring steam to maintain pumpability. The chief engineer is on deck supervising cargo operations. The motorman reports that the gauge glass shows water at the bottom of the visible range.
1. State the immediate actions you take and the checks you make before attempting to restart the boiler.
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Immediate actions:
- Do not restart the burner. Confirm the burner is off and the fuel supply is isolated. A dry-fired boiler can be severely damaged.
- Check the gauge glass. Blow through the gauge glass to confirm the reading is genuine and not a false indication caused by a blocked connection. Compare with the level controller indication and the low water level switches.
- Check feedwater supply. Confirm the feedwater pump is running, the feed tank has water, and the feedwater valve is open. A common cause is feed pump failure or a closed valve.
- Check for leaks. Inspect the boiler, fittings, and feed line for leaks. A sudden loss of water may indicate a tube or fitting failure.
Before restarting:
- Confirm the actual water level is restored to the normal working level in the gauge glass.
- Test both low water level switches and the alarm.
- Confirm the burner sequence and flame failure device are functioning.
- Only then restart the burner at low fire and monitor the level closely.
Cargo consideration: Inform the chief engineer and the deck watch that steam may be interrupted. Assess how long the cargo can remain without heating before pumpability is affected, and plan accordingly.
2. The gauge glass shows water at the bottom of the range, but the level controller indicates normal level. How do you resolve the discrepancy?
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The gauge glass is the primary local indication and must be trusted until proven wrong.
- Blow through the gauge glass. Close the top cock, open the drain, then close the bottom cock and open the top cock to blow through. Repeat in the correct sequence. If water returns to a normal level, the original reading was a false low caused by a blocked water connection.
- If the glass remains low, suspect a blocked steam connection (giving a false high) or a genuine low level with a faulty level controller. Check the controller's sensing lines for blockage or leakage.
- Cross-check. Compare with any independent level indication, such as a test cock or a second gauge glass if fitted. Check the feedwater valve position and feed pump running status.
- Do not assume the controller is correct. A level controller that reads high while the boiler is actually low will keep the feedwater valve closed, which is dangerous. If in doubt, operate the feedwater valve manually and observe the gauge glass.
- Record and report. Log the findings and inform the chief engineer. If a sensing line is blocked, it must be cleared before the boiler is returned to automatic control.