- Close the section isolating valve, this will raise an alarm indicating zone isolation
- Now, open the test valve, if no water comes out, then it means the NR valve placed after the section isolating valve is not leaking.
- Since, the section after the NR valve remains pressurized, opening of the drain valve will cause the water pressure in the section line to decrease. A pressure switch sensor senses the decreased pressure & raises an alarm.
- Now, close the drain valve, open the section isolating stop valve. To check the flow switch, open the flow test switch to activate an alarm.
- Allthe above alarms will be indicated on the navigation bridge, E/room as well as in the Fire Control Room. The alarm will also indicate the particular zone from where it has risen.
- Ifall the alarm conditions are satisfied, close all the testing valves, open the section isolating valve, purge the sprinkler line by air and again keep the line pressurized. Check from the pressure gauge, that proper pressure has been maintained or not
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 doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the dirrection 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 More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.