Marine Engineering Study Materials

What are the causes of starting air line explosion on ships ?

1. The main cause of starting airline explosion is the leaking starting air valve or jamming at open position of the valve.
2. Initially, the oil which is discharged from the air compressor to starting air line system, it will deposit as a thin moist film on the internal surface of the pipes but not ready to combustion.
3. If starting air valve leaked or jammed at open position, hot gas or flame may enter the starting air manifold, vaporize the oil and set the fire to oil mist and greasy matters, which generally deposit on the surface.
4. At that condition, mostly arrival first start for manoeuvring time, high pressure compressed air coming into contact with the fire and may cause explosion.

How to prevent starting the air line explosion ?

1. Regular overhaul and maintenance of starting air valve.
2. Before departure, test the air starting valve leakage.
3. Regular drain off the air bottle drain valve.
4. Regular drain off air starting system.
5. Regular cleaning of the compressor suction air fitter and use oil wetted suction filter.
6. Feed minimum absolute cylinder lubrication to compressor.

What are the safety devices on starting air line ?

1. Spring loaded safety valve or bursting disc. (if bursting disc fitted, no need of relief valve)
2. Flame trap. (At Joint where manifold to each cylinder starting line)
3. Starting air line drain valve. (Inlet of automatic air starting valve)
4. Turning gear interlock 
5. Reversing interlock 

How to test starting air valve leakage of main engine on ships ?

When Engine Running

• By hand touch feeling to adjacent pipe to the valve while in engine is operating.         
• If leak, we can feel the pipe hotter than others.

When Engine Stopped

• Shut the isolating valve of starting air distributor        
• All indicator cocks must be opened    
• Disengage the turning gear
• Open the main air bottle stop valve
• Set the control lever to starting position       
• Check all the indicator cocks   
• Escape of air through indicator cock will show a leaking starting valve
• It should be replaced immediately.    

Write a note on bursting disc arrangement on main engine ?

• When starting air line explosion occurs, bursting disc burst out of safety tube, the outer hood can be moved round just far enough to blank off the holes in the inner hood, thus preventing air leaks when the engine continue using air.
• It is only used for emergency and the bursting disc should be renewed as soon as possible.
• The detector fixed to the safety cap will by bent out at the explosion and it tells at a glance which disc has burst.

What are the bursting disc maintenance on ships ?

• For renewable type, renew after complete running hours.
• For reusable type, annealing must be done.

Reference:

Oral Guide by – MIN ZAR TAR