Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.
Issue link: http://uscgproceedings.epubxp.com/i/578020
35 Fall 2015 Proceedings www.uscg.mil/proceedings The term "liquefed gas carrier" (LGC) covers a broad range of vessel types and includes more than 400 liquefed natural gas (LNG) carriers and more than 1,100 liquefed petroleum gas (LPG) or petrochemical gas carriers operating world- wide. 1 Carrying certain gas cargoes on LGCs in a liquefed state versus a gaseous state reduces the volume immensely. For example, liquefaction of methane gas (LNG) and liquefac- tion of propane gas (LPG) reduces the volume by factors of 600 and 270, respectively. 2 However, when liquefed, these cargoes become more challenging to store, due to the low temperature and/or high pressure required to keep the cargo in the liquid state. Careful vessel design and operation, coupled with inter- national safety codes and strictly enforced industry guide- lines, helps to ensure safe liquefed gas shipment. Thus, with increased shale oil and natural gas production, the U.S. is set to become a major liquefied gas exporter. LPG Carriers LPG carriers transport heavier hydrocarbon gases, which are typically produced from oil refning processes. Currently, the largest propor- tion of liquefed petroleum gas is produced in the Arabian Gulf states and shipped to northeastern Asia. 3 Large liquefed petroleum gas carriers transport the cargo fully refrigerated at atmospheric pres- sure, while smaller quantities are transported either under pressure or semi-refrigerated. LNG Carriers Large volumes of methane are only carried in the liquefed state. The largest liquefed natural gas producers are currently Qatar, Australia, Malay- sia, and Indonesia. The largest consumers (used to generate power) are Japan, Korea, and China. 4 The proposed expansion in U.S. LNG export capability will lead to a cor- responding ramp-up in U.S. port calls for liquefed natural gas carriers. Further, the increasing number of U.S. LNG liquefaction facilities either under construction or awaiting approval will create a fourfold increase in the number of liquefed natural gas carrier transits by 2016. By 2020, the Sabine Pass on the Texas/Louisiana border may see hundreds of gas carrier transits per year, marking a major step-change in the vol- ume of world liquefed natural gas exports. 5 Conditions of Carriage There are three conditions of carriage for liquefed gas car- goes: • Fully refrigerated: The cargo is carried at or very close to atmospheric pressure. Liquefed Gas Carriers Trends, routes, and inspections. by Mr. MichAEl dAvison Project Development Manager BG Group Ship Liquefed Gas Production, Transportation, and Use LT dAllAs sMith Marine Inspector U.S. Coast Guard Liquefed Gas Carrier National Center of Expertise An LNG carrier alongside the terminal at Elba Island, Georgia. All photos courtesy of Michael Davison, Project Development Manager, BG Group. continued on page 37