What is the purpose of water spray arrangement around the deck LNG fuel tanks of a Dual Fuel VLCC?
When LNG in liquid condition drop on steel plate of the ship (in an accident), such steel plate will be cracked due to very low temperature of LNG.
To avoid such direct contact, barrier between LNG and steel plate will be necessary.
As such, water spray is required on Gas Carrier Code.
According to IGF Code 11.5.1 A water spray system shall be installed for cooling and fire prevention to cover exposed parts of fuel storage tank(s) located on open deck.
11.5.2 The water spray system shall also provide coverage for boundaries of the superstructures, compressor rooms, pump-rooms, cargo control rooms, bunkering control stations, bunkering stations and any other normally occupied deck houses that face the storage tank on open decks unless the tank is located 10 metres or more from the boundaries
Further to DCKim’s response, as metals cool, they lose their ductility. Mild steel” becomes brittle at about -10°C. Normal hull steel is susceptible to brittle fracture at cryogenic temperatures. Steel structures that come into contact with LNG can easily crack if stressed, impairing ship integrity
This is britlle fracture on carbon steel deck plate to illustrate. Note that this is not valide for stainless steel.
Thanks for rare, interesting but valuable spot report.