Progress: Addressed, Not Adequately
DOT Relevance: 178
DOT requires that non-liquefied compressed gases be shipped in specification containers. Composite cylinders are not included in DOT cylinder specifications. Therefore, composite cylinders are only allowed in service by obtaining a special permit in accordance with 49 CFR 107 Subpart B. Section 178 Subpart H deals specifically with portable tank specifications, which contain liquefiable gases with a liquid/gas interface.
Fluids held in 178 Subpart H portable tanks must currently be made of steel with welded construction in accordance with ASME Section VIII. Portable tanks are held at relatively low pressures, which would imply storage of hydrogen would be cryogenic or in the form of a solution or chemical hydride. Light weight is one consideration for portable tanks, so that they can be transported more easily. Composite tanks are lighter in weight than steel tanks, although this would be less significant with liquefied contents at lower pressures. Consideration must be given to temperature compatibility of composite materials, to thermal stresses in the composite tank, and dynamic loads.
Composite tanks have been used in cryogenic applications, but their use in transportation is insignificant. Composite tanks have been used to transport liquids, but these have generally been at low internal pressure.
DOT currently has no composite portable tank standards. Composite tanks have been developed for containing pressurized liquid hydrogen, but their use in transportation has been limited. Composite tanks for liquids are generally not at high pressure. There is likely insufficient transportation experience with portable composite tanks to deal with standards development at this time.
ASME's Boiler and Pressure Vessel project team on hydrogen tanks is addressing high pressure gas storage in metal and composite tanks. The work plan includes a proposed new article KD-10 to Section VIII-3, a code case on composite tanks for Section VIII-3, and a revision to code case 2390 on metal lined composite reinforced circumferentially wrapped pressure vessels under Section VIII-3. Transport tanks may also be included in Section XII.
The industry and DOT should monitor the need for composite portable tanks. Design studies may be required to assess the practicality of using composite portable tanks to transport hydrogen or hydrogen compounds. DOT should address any applications with special permits until a sufficient data base of use exists and a larger market need exists.