TUBE LEAK IN A WATER TUBE BOILER

(i) When the amount of leakage is small:

• A slight drop in boiler water level (increased feed water consumption).
• A slight increase in the feed water flow/ make-up.
• A hissing/ steam sound in the boiler (steam escaping into the gas side).
• A slight increase in the boiler pressure/ temperature fluctuation.
• Moisture/ steam at the boiler casing/ inspection openings.

(ii) When the amount of leakage is large:

• A rapid drop in boiler water level (alarm/ low-level trip).
• A large increase in feed water flow.
• A loud steam/ water leak sound.
• Steam/ water escaping from the boiler casing, flue or stack.
• A drop in boiler pressure/ steam output.
• Possible water hammer/ vibration.
• A rise in the flue gas temperature (less heat absorbed) or a change in the gas analysis.

(i) How it can be identified:

• The leaking tube is identified by inspection (steam/ water marks, or by pressurising the water side and observing the leak location).
• Within the tube bank, the leak is located by isolating sections/ by observing the steam/ water escaping from a specific tube, or by using a leak-detection method (e.g. pressurising and observing, or by the sound/ moisture at a specific tube).

(ii) Immediate actions and temporary repairs:

• Isolate the boiler: shut off the fuel/ firing, shut off the steam and feed water, and allow the boiler to cool and depressurise.
• Identify the leaking tube and plug it (temporary repair): fit a plug (tapered/ threaded or welded) at both ends of the tube (top and bottom) to isolate it, as per the maker/ Class-approved method.
• Pressure test the boiler to confirm the plugged tube is leak-tight.
• The boiler can then be returned to service (with the plugged tube) until a permanent repair (re-tubing) is carried out at the next opportunity.
• Record the plugging and, where required, obtain surveyor/ Class approval.