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LPG ships transport liquefied petroleum gas (LPG), which consists mainly of propane and butane or a mixture of these two hydrocarbons, including propylene and butylene, as well as various chemical products; in recent years, ethylene has also been included in the range of substances transported by such ships. Based on the different liquefaction conditions for carrying various gases, they are classified into full-pressure type (with a smaller loading capacity), semi-cold semi-pressure type (with a larger loading capacity), and full-cold type (with a large loading capacity). LPG carriers have special requirements in various aspects due to their specialized purpose; they present high technical challenges and represent the current level of shipbuilding technology. Their price is 2 to 3 times that of conventional transport ships of the same tonnage, making them ships with high technology and high added value. Classification of LPG ships: LPG ships are classified into three types based on the method of cargo transport: fully pressurized, semi-cold and semi-pressurized (cold pressurized), and fully cold type. (1) Total-pressure transportation, also known as normal-temperature pressure transportation, involves placing the goods under pressure at normal temperature that exceeds their vapor pressure, thereby turning the goods into a liquefied state. A few gases such as ethane, ethylene, and methane do not liquefy even when pressurized above their critical temperature. The holds of full-pressure transport ships do not require insulation or cryogenic cooling equipment. Typically, the maximum design temperature is 45°C, and the maximum design pressure ranges between 1.75 and 2.0 MPa. China’s first 3,000 m3 LPG ship, built by Jiangnan Shipyard, had a design working pressure of 1.75 MPa; typically, the tank capacity of full-pressure LPG ships is below 5,000 m3. (2) Semi-cold semi-pressure transport, also known as low-temperature pressure transport, saw its first vessel built in 1959, with a capacity of 2100 m3. In early 1960s in Europe, as research on cryogenic technology matured, a large number of such facilities were built one after another. Currently, the German fleet is the most common to see. In the early days, the cooling temperature for such ships was around –5°C, with a pressure of about 0.8 MPa; they were used to transport liquefied gas in a manner similar to fully pressurized LPG ships, and very few of them are built these days. Recently, such ships have been divided into two categories: the majority have a cooling temperature of –48°C, while a few used for transporting ethylene have a cooling temperature of –104°C. The operating pressure ranges from 0.5 to 0.8 MPa. The 4200 m3 and 16500 m3 LPG ships built by Jiangnan Shipyard belong to these two ship types respectively. Typically, the maximum tank capacity of such ships does not exceed 25,000 m3, and the newly developed 30,000 m3 LPG ship is the largest of its kind. (3) Fully refrigerated transport, also known as the low-temperature at atmospheric pressure type, involves storing liquefied gas in pressure-resistant tanks where it remains in a boiling state at atmospheric pressure. The design pressure for liquid tanks is generally 0.025 MPa. The volume of a single tank is rarely limited, making it suitable for building large ships; their capacity usually ranges from 50,000 to 100,000 m3. Tank structure types: (1) non-independent integral tank type; (2) internally insulated storage tank type; (3) independent tank type. This tank can be divided into three types: A, B, and C. None of them are part of the ship’s structure, and they are self-sustaining. Type A independent tank: This type of liquid tank is typically composed of a planar structure, with a maximum allowable design pressure of not more than 0.07 MPa. It is widely used on large fully refrigerated ships, and the operating temperature is not lower than –55°C. Type B independent cabin: Accurate structural stress analysis and model testing are required, including the use of finite element methods and shell theory; in some cases, frame analysis techniques can also be appropriately employed. Buckling, fatigue life, and plastic deformation are all taken into consideration. The tank types are prismatic and rotatable spherical, with a pressure of less than 0.07 MPa. This type is widely used in LNG carriers. Type C independent compartment: Type C compartments come in single-tank, double-ear, and three-leaf types, and are designed in accordance with pressure vessel standards. The design pressure is usually taken as 1.8 MPa, not exceeding 2 MPa. All the full-pressure and semi-cooled semi-pressure LPG ships currently built in our country fall into this category. This ship does not require shielding, and its technical status is mature. Reports on LPG carriers at home and abroad: The “Franders Tenacity” is an 84,000-cubic-meter fully refrigerated LPG/liquid ammonia carrier built in May 1996 at the Sakai Shipyard of Kawasaki Heavy Industries in Japan; it represents the largest class of vessels in terms of capacity among LPG carriers. Total length: 230.00 meters, beam: 219.70 meters, draft: 36.00 meters, depth: 21.90 meters, draft: 11.60 meters, gross tonnage: 47,027 gross tons; load capacity: 54,135 tons. Main engine model: MAN B&W 5S70MC diesel engine manufactured by Kawasaki; maximum power: 18,300 horsepower; service speed: 17.5 knots. This ship is primarily used for transporting goods such as propane, butane, and anhydrous ammonia. It features an IMO-approved Type A double-hull structure; all 4 cargo tanks are prismatic in shape and are made of carbon-manganese alloy steel, allowing the temperature in the cargo tanks to be reduced as low as minus 48°C. Each cargo hold is equipped with 2 electric deep well pumps with a loading/unloading speed of 600 meters per hour, 2 booster pumps, and a cargo hold heating system that enables the transport of liquefied gas to shore at temperatures below its critical point. The 22,000 m3 semi-cold semi-pressure liquefied gas carrier manufactured by Jiangnan Shipbuilding (Group) Co., Ltd. is capable of transporting three different densities of liquefied gas as well as certain chemicals. Its minimum designed operating temperature is -104°C, with a maximum pressure of 4.7 bar. The main research contents include: developing a ship design that can meet various draft conditions ； It solved the problem of ensuring overall stability under a wide variety of cargo types and loading conditions (with nearly 3,000 different hull damage scenarios), thereby greatly enhancing the safety of the ship ； The key technology for safe launching under deckless and weak structural conditions has been achieved ； The key welding techniques for constructing liquid storage tanks from ultra-low temperature (-104°C), high-strength, high-nickel alloy steel materials have been mastered ； Achieved modular manufacturing technology for the complex liquid cargo system equipment on domestic liquefied gas carriers, earning a good reputation in the global shipbuilding market. Notable large fully-cooled LPG carriers abroad include the World Bridgestone 74,000 m3 fully-cooled LPG carrier, the Yuyo Maru 10 47,500 m3 LPG/petroleum products hybrid carrier, the Danian Gas 26,000 m3 fully-cooled LPG carrier, the Gaz Fountain 40,232 m3 fully-cooled LPG carrier, and the La Forge 70,793 m3 LPG carrier built by Nippon Kokan. The table below lists some of the key specifications for LPG carriers both domestically and internationally: Loading capacity, Transport mode. Jiangnan Shipbuilding: 22,000 m3, semi-cold and semi-pressure type; Hudong Shipbuilding: 8,400 m3, semi-pressure and semi-cold type; Franders Tenacity: 84,000 m3, fully cold type, Type A; World Bridgestone: 74,000 m3, fully cold type; Danian Ga: 26,000 m3, fully cold type; Gaz Fountain: 40,232 m3, fully cold type