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49 Fall 2015 Proceedings www.uscg.mil/proceedings B, and C tanks. LNG tanks can also be non-independent tanks, which include the membrane and semi-membrane types. Tank Types The International Code for the Construction and Equip- ment of Ships Carrying Liquefed Gases in Bulk (IGC Code) defnes three categories for independent LNG tanks, which are self-supporting tanks that do not rely on a ship's struc- ture for strength. Type A independent tanks: are designed primarily using recognized standards of classical ship structural analysis, constructed of a plane surface, and prismatic in shape. The IGC Code, where the minimum design temperature is below -10°C, requires a complete secondary barrier capable of con- taining the cargo for a period of 15 days in the event of a ruptured or leaking tank. Type B independent tanks: use model tests and refned tools and analysis methods to determine stress levels, fatigue life, and crack-propagation characteristics. A partial secondary barrier, which can consist of a spray shield and drip pans, is required for independent Type B tanks with minimum design temperatures below -10°C. Type C independent tanks: are pressure vessels that are designed for pressures greater than two bar 1 and are cylin- drical or spherical. Type C tanks can be designed for much higher vapor space pressures than Type A and Type B tanks, and they don't require a secondary barrier. Membrane, or non-independent tanks: are non-self-sup- porting tanks that consist of a thin layer (called a membrane) supported through insulation by the adjacent hull structure. This containment system requires a complete secondary barrier capable of containing the cargo for 15 days. Semi-membrane tanks: are non-self-supporting when loaded. Only parts of the tank are supported (through insu- lation) by the adjacent hull structure, whereas the rounded parts of this layer connecting the supported parts are designed to also accommodate thermal and other expan- sion or contraction. The majority of proposed LNG tank barges utilize either Type C tanks or membrane tanks. 2 Another unique challenge for the LNG bunker barge is the large variation among ships the barges plan to serve. Trans- fer pipes and connections have yet to be standardized, fuel- loading fange access and location may vary greatly, and vapor management systems may also differ for each vessel. 3 Regulatory Challenges The Coast Guard must anticipate quickly advancing tech- nologies in the LNG maritime domain to ensure adequate safety requirements for this valuable product stream. From a regulatory perspective, liquefed natural gas cargo trans- port has a 50-year history. Classifcation rules, international regulations, and fag state requirements that support the ship design, construction, and service are mature. However, as a virtually new asset class, LNG bunkering barges face several technical and regulatory challenges, including: • new vessel specifcations and service requirements, • bunkering practices to transfer the LNG from the barge to gas-fueled ships, • developing new regulations surrounding LNG trans- port by barge. For example, 46 CFR Subchapter D regulations are not suit- able for LNG's cryogenic temperatures. While there is guid- ance for cryogenic cargoes in 46 CFR Subchapter O — Cer- tain Bulk Dangerous Cargoes Part 154, safety standards for self-propelled vessels carrying bulk liquefed gases, they are applicable to self-propelled vessels only, thereby excluding barges. Although guidance is also available in international mari- time standards (the IGC Code applies to liquefed gas car- riers), barges differ from liquefed gas carriers (LGCs) in a number of critical areas, including: • regulatory applicability, • propulsion, • size, • manning and personnel, • voyage length and routes, • primary fag state. LGCs are generally larger than barges and can carry up to 10 times more cargo than a typical barge. LNG carriers' cargo capacities range from 18,800 m 3 to 266,000 m 3 , with a feet average LNG capacity of 153,000 m 3 . 4 By contrast, pro- posed LNG barge capacities are currently projected to be between 1,000 m 3 to 20,000 m 3 5,6 The only U.S.-fagged LNG barge, the barge Massachusetts (no longer in U.S. service), was 5,000 m 3 . 7 Another difference between LGCs and barges is their fag and operating zone. Barges are generally domestic vessels, or U.S.-flagged, and are likely to operate in U.S. coastal waterways. This is unlike most LGCs, which are foreign- fagged and travel internationally, triggering IGC applica- bilities. As such, the barge community may use current U.S. LNG carrier regulations and the IGC Code as guidance, continued on page 51