An LNG carrier is a vessel specifically designed to trade and transport liquefied natural gas (LNG). LNG is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6). The LNG ships have a cargo carrying capacity between 125,000 cum to 260,000 cum. The most popular size is up to 180 000 cum.
In order to facilitate transport, natural gas is cooled down to approximately −163 °C (−261 °F) at atmospheric pressure, at which point the gas condenses to a liquid. The tanks on board an LNG carrier effectively function as giant thermoses to keep the liquid gas cold during storage.
Gas carriers are specifically designed to carry bulk gases. These vessels are categorized into two main segments: LNG and LPG.
While LNG vessels are designed to transport liquefied natural gas, LPG vessels are built to carry liquefied petroleum gas (LPG). To learn more about LPG vessels, you can read our detailed article on the different types and sizes of LPG carriers.
LNG carriers can be classified into the categories in term of the cargo containment system:
This system is named after the Norwegian company which designed them (Kvaerner Moss). Most of these vessels have 4-5 tanks. Moss tanks have a working pressure of up to 22 kPa (3.2 psi), but the working pressure can be raised foran emergency discharge.
The self-supporting prismatic type B tank is designed by Ishikawajima-Harima Heavy Industries. Due to several incidents in the past, these tanks were designed to avoid damage due to incidents occurred inside membrane LNG tanks. The design is implemented in very few vessels.
These vessels are designed by Technigas and are a membrane type design. The membrane consists of stainless steel and the tanks have a 1.2mm waffle pattern' to absorb the thermal contraction when the tank is cooled down.
This design designed by Gaztransport consists of primary and secondary membranes made up of a material Invar which has no thermal contraction. The insulation is made out of plywood boxes filled with perlite and continuously flushed with nitrogen gas. The integrity of both membranes is permanently monitored by detection of hydrocarbon in the nitrogen.
Invar, FeNi36 (64FeNi in the US), is a nickel–iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α).
C-type tanks are quite common in the small scale LNG segments. These tanks are designed as cryogenic pressure vessels, using conventional pressure vessel codes (very often vapour pressure). The design pressure for these tanks is in ranges above 2000 mbar. The most common shapes for these tanks are cylindrical and bi-lobe. Type ‘C’ tanks are used in both, LPG and LNG carriers.
These tanks have a prismatic tanks shape and maximize the use of the vessel’s tanks, ensuring a flat deck without losing cargo capacity. A self supporting tank structure enabling parallel building activities. The design aim to optimize the cargo carrying capacity volume, the thermal insulation performance in tank shape and hull design.
In Maritime Optima we have used the cum. sizes to divide the vessels into sub segments. In addition to the pre-defined segments, you're able to search for vessels based on your own criteria, i.e. technical details such as summer deadweight (SDTW), draft, TPC and cubic capacity to name a few. With the smart search feature you can even search for vessels based on where the vessels departed from, their current location and an entire voyage (from-to).
