Korea imports LNG from 16 contries (as of 2016) including Qatar, Australia, Oman, and Malaysia. It takes about 15 days for an LNG carrier to make a round trip to Southeast Asia, and about a month to the Middel East.
On arrival in Korea, the, LNG carrier is delivered to the jetty in a LNG terminal by 4 Tug Boats,
and after arriving at the jetty, it is fixed at the pier with a mooring rope to minimize the movement of the ship during unloading.
When the LNG carrier is fixed in place, three LNG unloading arms and one NG arm are connected, and the LNG is transferred through the unloading piping to the onshore storage tanks using the transfer pumps on the LNG carrier side.
The reason for connecting the NG arm is to compensate for reduced pressures in the carrier tanks caused by level decrease of LNG tanks on the carrier side.
This can cause damage to the tanks, -Boil-off gas (BOG) generated at the production base is supplied to the ship to compensate the pressures.
A lot of BOG is generated in the early stage of unloading because LNG evaporates while LNG is being unloaded through the unloading piping,
where the temperature is partially elevated. The amount of LNG loaded on one LNG carrier is usually 125,000 m3 (approx. 57,000 tons) or 135,000 m3 (approx. 62,000 tons).
When LNG unloading starts, a portion of LNG is collected from the unloading piping to analyze its composition, heating value, and weight, and when the unloading is completed,
the LNG carrier is separated from the unloading facilities. It takes approx. 12 hours to unload LNG to the LNG storage tanks in the terminals,
but the ship docks for approx. 21 hours because of the unloading preparation process, loading of food and repair materials needed on the ship, and changing crew.