Q. What are the air bottle maintenance and inspections?
Ans:
a. Regularly drain the bottle of water and oil
b. Regular inspection to ensure that the internal condition of the bottle is good
c. Check for corrosion both externally and internally
d. Inside coating, COPAL varnish condition to be checked to ensure that it is unbroken and no peeling is taking place
e. Welding seem to be checked, carry out dye-penetrant test at suspected areas.
The tell-tale hole between the lap welding seams of the doubler plate / ring to be checked for leaks in service to ensure that the internal welding is intact
g. Face of the man hole to be checked for pitting marks
h. Drain should be clear
i. All points of high stress and corrosion are to be thoroughly checked viz. welds, supports braces, the bottom of the bottle where water/oil is collected. Pay attention to the zone of water line.
j. Check for leaks at the mounted valve glands/flanges, carry out inspection of the valve face and seat for wire drawing effect
k. A timing check with the air bottle completely charged and isolated will give a good idea of the intactness of the pressure vessel
l. The safety/relief valve setting to be inspected as per the class requirement
m. Regularly check the alarms and monitoring equipment for proper functioning
Q. Explain the air bottle entry procedure.
Ans:
a. Inspection is to be carried out when the receiver capacity is not required for maneuvering
b. Receiver properly isolated, depressurized and notice pasted
c. The internal pressure is to be checked by the pressure gauge and by opening the drain valve
d. Open the manhole door carefully and ventilate the air bottle
e. Obtain an enclosed space permit and comply with it
f. Ventilation is to be maintained during the entire time of enclosed space entry
Q. What action should be taken in case of corrosion/wasting observed on air bottle?
Ans:
MINOR: Clean the site of corrosion, observe the varnish manufacturer instructions for surface finishing prior applying the coat. Apply new coat of the varnish.
MAJOR: The site has to be cleaned and re-varnished as above. The air bottle has to be derated.
In case of excessive the entire bottle has to be replaced.
The derating procedure should be carried out as follows:
a. The extent of the derating is determined by the class surveyor to a value which ensures the safe limit of the hoop stress at this reduced thickness of the shell plating
b. The derating should not violate the starting air requirements for consecutive starts of the main propulsion engine
c. The setting of the safety/relief valve, should be set not exceeding 10% of the maximum working pressure after derating
d. The cut in and cut out pressure switches for compressor automation should be readjusted
For these reasons the air pressure vessels on board ship are fabricated to allow for derating in future still complying with the consecutive start requirements of the propulsion engine.