.bmd .boiler manhole door .manhole door .boiler door
Procedure for opening boiler manhole door:
- Boiler depressurized
- Boiler sufficiently cooled down
- Drain the boiler water fully
- Hold the top door with chain block before opening the manhole door nut. Open the top manhole door first to make sure the water is fully discharged
- After opening top door, a sounding tape with water finding paste is inserted inside a tube to check whether the boiler is empty or not.
- Then open bottom manhole door.
Why manhole door is elliptical
- any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole.
- More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out.
- To compensate for the loss of material in the shell due to opening, a compensating ring has to be provided around the opening.
- The thickness of the ring depends on the axis length along the direction in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum.
→Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating
→Circumferential stress: Pd/4t
Why manhole door is fitted inside
The manhole door of any pressure vessel is elliptical in shape and fitted from the inner side for safety reasons.
If there is any hidden pocket of pressure (that is not indicated in pressure gauge) because of its shape the door will not come out of the boiler/air bottle and thus preventing human injury.
To bring it out the door is inclined to some extent and bring it out.
What is the advantages of reflex plate gauge glass?
- It is very thick and less chances of crack or break down
- With this type of gauge glass water level can be seen from distance
what is your course of action, if your boiler gauge glass is leaking ?
- Ans: There are 2 gauge glasses.
- If one gauge glass leaks, it is isolated and not used. The steam and water valves are shut and drain valve opened.
- At the first opportunity when the boiler is out of service and not under pressure, the leaking gauge glass is safely renewed.
- Trying to repair/replace leaking gauge under pressure by shutting the steam and water valves is not safe.