Cryogenic fuel tanks

Cryogenic fuel tanks are essential components for space transportation systems. Materials for cryogenic fuel tanks must safely carry pressure, external structural loads, resist leakage, and operate over an extremely wide temperature range. Aramids exhibit a wide range in service temperature and are therefore candidates for such applications. A wide variety of skin and core materials have been tested for helium gas permeability. It turned out that Nomex is superior in comparison to Kevlar . A low level of permeability could be achieved, which meets the requirements. 

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Being very clean and pure minimizes the materials compatibility concerns for LNG. However, LNG presents a new materials compatibility concern operation at cryogenic temperatures.3 For LNG fuel tanks, stainless steel is the preferred material and instances of materials compatibility problems are rare. Aluminum also has been used as a tank material without materials compatibility problems. Carbon steels are not used since their performance at low temperatures is questionable, i.e., they become susceptible to brittle fractures. While tanks are usually made from stainless steel or aluminum, LNG fittings may use some nickel alloys, brass, and copper, in addition to stainless steel and aluminum. 

The above discussion about LNG materials compatibility focuses on the LNG fuel tank and portions of the LNG fuel system that are subjected to cryogenic temperatures. In LNG fuel systems there is a portion of the system downstream in which only LNG vapor at low pressures is present. This portion of the LNG fuel system is not subject to the demands placed on materials for service at cryogenic temperatures. 

Cryogenic fuels like liquid hydrogen are more difficult to handle and substantially more difficult to store compared to hydrocarbon fuels like gasoline or aviation kerosene. Even with highly-insulated double-walled, vacuum-jacketed storage tanks liquid hydrogen can evaporate at a rate of almost 9% per day. 

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