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Some of the common repair work carried out on the marine boiler while on board the ship is plugging of the tubes and replacing the leaky manhole joints. Other major repairs like the renewal of the damaged tubes and furnace rebuilding must be carried out in the dry dock. The plugging of the boiler leaky tube is a temporary repair which must be carried out in order to fire the boiler. Whatever the situation, and in any condition the boiler must run to supply the working steam.
When the gasket becomes damaged or gets old, smoke starts to come out of the boiler in the case of the water tube boiler. In the smoke tube boiler, the water starts to leak outside the boiler. This must be repaired onboard by replacing the leaky manhole joints.
Replacement of a Leaky Manhole Joint:
- Maintain proper spigot clearance- 1.5 mm to position the door centrally for evenly loading the gasket.
- Never use an old gasket.
- Do not over strain the door studs, which may stretch.
- Pull-up studs by re-tightening the nut after steam rising or warming up.
- Avoid causing damage to door by holding it by a rope and gently lowering it inside or taking it out.
- Mark the dogs and nuts to fit back correctly in the same door.
- Check for wear and tear on the studs and nuts.
- Carefully check the matting/ landing surface for corrosion and erosion on the door and boiler before reassembling.
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Repairs In Smoke Tube Boilers:
Procedure for Plugging of a Damaged / Busted Smoke Tube:
- Hydrostatic testing to mark the leaky tubes.
- Cut the tubes on one end and clear of the tube plate. At the other end the tube is collapsed inside the tube plate.
- Pull out the tube from the collapsed end.
- Insert a short tube into the tube plate and weld it in place.
- Lap the spare tapered plugs on both stud ends in the tube plates.
- Insert the tube plugs and tack weld it.
- Alternatively, the plugs can be held in place by a long steel bar threaded and bolted at both ends.
- Hydrostatic pressure test to confirm no leaks.
- Flush up the boiler and re-inspect the plugs for leaks under full steam pressure.
Temporary Repairing Procedure to Rectify the Leakage in Smoke Tube:
- Stop the burner, allow the boiler to cool and remove the soot.
- Allow boiler to depressurize, and open the blow down valve to drain the boiler.
- Enter the boiler flue box and cut a hole in the side of the relevant smoke tube.
- Clean the rim of the smoke tube with a wire brush.
- Cut a circular plate (15 mm thick) of the same diameter as the smoke tube and chamfer the top edge to 30 degrees by grinding.
- Fit the plate into the top of the smoke tube and weld it in position as shown.
- Enter the boiler furnace and cut a similar hole in this end of the relevant smoke tube.
- Repeat steps 4 to 6 for lower plate.
- Refill boiler and check for leaks before start-up.
- Start up boiler and check for leaks when pressurized.
Note: Any temporary repair to smoke tubes or boiler tubes should receive more permanent attention as soon as conveniently possible.
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Repairs In Water Tube Boiler:
Instruction for Plugging / Repair of Water Tube Boiler & Economizer:
- In case of tube failure, steam pressure has to be removed and the oil burner dismantled.
- If the leakage is readily visible from the burner hole, the boiler can be emptied and repairs commence.
- Otherwise, the boiler is given pressure by means of the feed pump. The position of the leakage will be indicated by the water flow.
- This flow may not be visible from the burner hole. If it is not visible, remove the inspection door and enter the furnace. If the tube failure is still not found, then enter the generating tube section. From here the bottom of the membrane walls and generating tubes can be inspected for leakage.
- If the leakage has resulted from the membrane walls or generating tube, the inspection door at the smoke connection pipe must be removed, and the generating tube/ membrane tube in which the failure has occurred is pointed out.
- The leakage may also result from economizer.
- By removing the inspection door at the bottom of the economizer, it can be determined which uptake has caused the leakage.
- If necessary other inspection doors should be removed to point out the damage register.
- When a damaged tube or convection register has been removed, and the remaining tube studs have been repaired/ plugged a new tube or register should be mounted as soon as possible.
- Operation for longer periods with one or more registers missing involves the risk of further damage to the boiler due to increasing heat leads on the parts next to the ones removed.