Liquefied natural gas carrier is short for LNG carrier, mainly used for transporting liquefied natural gas. The main component of liquefied natural gas is methane, for facilitate transportation, it is usually liquefied at low temperature (-165°C) at normal pressure. LNG vessel is a specially designed ship for liquefied gas at low temperature, it is a kind of “marine super freezing tanker” and known as one of the most difficult vessel types to build.  It can only be built in 13 shipyards in United States, China, Japan, South Korea and a few European countries 

LNG in the cargo hold will evaporate due to shaking and the input of heat from the environment during transportation. In order to meet the requirements of the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC) about cargo tank pressure level, special equipment is installed to eliminate the excess natural gas, which will be leading to gas waste. In order to solve the problem, different refrigeration liquefaction technologies are used to liquefied the evaporated natural gas and sends them back to the tank, ensure keeping no gas loss.