GAZ CARRIER - a watercraft for the transportation of liquefied gases (liquids with an absolute vapour pressure of more than 274.7 kPa at the temperature about 37.8 ° C). Gas carriers are distinguished by purpose, method of transportation of liquefied gas, as well as by design of the watercraft and its cargo (gas) tanks.
By destination, gas carriers are divided into two main groups: for liquefied petroleum gases (LPG) - propylene, propane, butane, etc.; for natural gas (LNG) - mainly methane. Watercrafts of the first group transport also liquefied gases, which are close to LPG in their physicochemical properties, with a boiling point not lower than -50 ° C (for example, ammonia, butadiene, vinyl chloride). Transportation of LPG and similar gases is carried out: under pressure (up to 1.8 MPa) in a cooled state (-48-50 ° С); combined method at a low temperature (about 10-20 ° C) and a pressure not less than 750 kPa. The latter is used mainly on watercrafts with a carrying capacity of up to 8 thousand tons. LNG is transported exclusively in a cooled state (at the temperature about -162 ° C). The design of the gas carrier and its cargo tanks is engineered according to the type of transported liquefied gas, its degree of danger to the crew and the environment, and the method of transportation. Tanks are divided into built-in, membrane, semi-membrane and supplementary ones.