You are here: Archives > March 2009 > Metal Hydrides Transportation and Shipment of Hydrogen in Metal Hydride Assemblies Robert Wichert, U.S. Fuel Cell Council As was reported previously in the Hydrogen Safety Report in October of 2007, prior to 2005 hydrogen stored in metal hydride assemblies could not be properly shipped or transported in normal commerce at all.  Although hydrogen could be shipped in compressed form, and metal hydride material could be shipped alone, the shipment of hydrogen stored in metal hydride assemblies was not covered by the United Nations Recommendations on the Transport of Dangerous Goods, Model Regulations.  Without such coverage, the various modes of transport and the nations that routinely adopt this document as the basis of their national regulations were not able to permit transportation of hydrogen stored in metal hydrides without special permissions that could be costly and time consuming.  This may have contributed to storage of hydrogen in metal hydrides not reaching its full potential as a safe and convenient method of hydrogen storage.  In an effort to correct this inadequacy, a Working Group under the auspices of the International Standards Organization Technical Committee 197 (ISO TC 197) wrote an international standard that forms the basis for international approval of hydrogen stored in metal hydride assemblies and their shipment.  This effort was led by Ned Stetson, then employed by Energy Conversion Devices (ECD).  Ned has subsequently been made an employee of the US Department of Energy in this same area of expertise.  The hydrogen community owes Mr. Ned Stetson a large debt of gratitude for his stalwart efforts to publish ISO 16111: 2008 Transportable gas storage devices -- Hydrogen absorbed in reversible metal hydride. Regulatory harmonization In an effort to harmonize the regulations for the transport of hydrogen in metal hydride storage systems, the US Fuel Cell Council petitioned the UN Sub-Committee of Experts on the Transport of Dangerous Goods, asking them to revise the United Nations Recommendations on the Transport of Dangerous Goods, Model Regulations.  The US Fuel Cell Council proposal can be found here: http://www.unece.org/trans/doc/2008/ac10c3/ ST-SG-AC10-C3-2008-74e.pdf The US Fuel Cell Council proposed using ISO 16111: 2008 Transportable gas storage devices - Hydrogen absorbed in reversible metal hydrideas the basic requirement for shipment of hydrogen stored in metal hydride assemblies.  If this proposal were adopted, shipment of hydrogen storage assemblies meeting ISO 16111 could become routine instead of requiring a special permit on a case-by-case basis.  During their consideration of the US Fuel Cell Council proposal, the United Nations Sub-Committee of Experts on the Transport of Dangerous Goods provided further clarification of the requirements that hydrogen stored in metal hydride assemblies must meet.  The US Fuel Cell Council proposal was finally accepted after much debate and revision.  The report on the meeting that accepted this proposal can be found here: http://www.unece.org/trans/doc/2009/ac10/ST-SG-AC10-36a1e.pdf The following is a summary of the requirements that will take effect with the publication of the 16th Edition of the United Nations Recommendations on the Transport of Dangerous Goods, Model Regulations in January of 2010. Metal hydride storage systems are formally defined as a pressure receptacle by the United Nations Recommendations on the Transport of Dangerous Goods, Model Regulations (UN Model Regulations). The specific definition of a metal hydride storage system is given in the UN Model Regulations as "Metal hydride storage system means a single complete hydrogen storage system, including a receptacle, metal hydride, pressure relief device, shut-off valve, service equipment and internal components used for the transport of hydrogen only." Metal hydride storage systems are limited to a water capacity (overall container volume) of 150 litres. Metal hydride storage systems are limited to a maximum developed pressure in use of 25 MPa. Steel components in contact with hydrogen must be suitable for hydrogen service, as designated by the “H” mark, properly applied in accordance with the UN Model Regulations. Metal hydride storage systems must meet the service conditions, design criteria, rated capacity, type tests, batch tests, routine tests, periodic tests, test pressure, rated charging pressure and provisions for pressure relief devices for transportable metal hydride storage systems specified in ISO 16111:2008. The hydrogen filling pressure of the metal hydride storage system must not exceed the rated charging pressure for the metal hydride storage system as specified in ISO 16111:2008 and as properly marked on the system. The periodic test interval for the metal hydride storage system must not exceed five years. The valve protection requirements of ISO 16111: 2008 must also be met. Specific requirements for the periodic batch testing of the pressure receptacles used, as well as the metal hydride assemblies, are given in a new paragraph of Part 6 of the UN Model Regulations.  New paragraph 6.2.1.5.3 additionally requires that these inspections and tests be performed on an adequate sample of the receptacles used in the construction of the metal hydride storage system. Testing of the mechanical characteristics of the material of construction; Verification of the minimum wall thickness; Verification of the homogeneity of the material for each manufacturing batch; Inspection of the external and internal conditions of the pressure receptacles; Inspection of the neck threads; Verification of the conformance with the design standard; A hydraulic pressure test is required for each and every pressure receptacle used in the construction of metal hydride storage systems. Pressure receptacles shall withstand the test pressure without expansion greater than that allowed in the design specification; NOTE: With the agreement of the competent authority, the hydraulic pressure test may be replaced by a test using a gas, where such an operation does not entail any danger. Every pressure receptacle that includes manufacturing defects must have an inspection and assessment of manufacturing defects and appropriate documentation of either repairing them or rendering the pressure receptacles unserviceable. In the case of welded pressure receptacles, particular attention shall be paid to the quality of the welds; An inspection of the markings on each pressure receptacle. New paragraph 6.2.1.5.3 additionally requires that these additional inspections and tests be performed on an adequate sample of the metal hydride storage systems. Verification of the homogeneity of the material for each manufacturing batch. Inspection of the neck threads, if applicable. Verification of the conformance with the design standard. Every metal hydride storage system that includes manufacturing defects must have an inspection and assessment of manufacturing defects and appropriate documentation of either repairing them or rendering the system unserviceable. An inspection of the external conditions of, and the markings on, the metal hydride storage system is required on each and every one. Every metal hydride storage system must successfully pass a leak tightness test as well as a functional test for satisfactory operation of the service equipment, such as valves. The following markings are required on the metal hydride storage system: The United Nations packaging symbol "ISO 16111" (the technical standard used for design, manufacture and testing); The character(s) identifying the country of approval as indicated by the distinguishing signs of motor vehicles in international traffic; The identity mark or stamp of the inspection body that is registered with the competent authority of the country authorizing the marking; The date of the initial inspection, the year (four digits) followed by the month (two digits) separated by a slash (i.e. "/"); The test pressure of the receptacle in bar, preceded by the letters "PH" and followed by the letters "BAR"; The rated charging pressure of the metal hydride storage system in bar, preceded by the letters "RCP" and followed by the letters "BAR"; The manufacturer's mark registered by the competent authority. When the country of manufacture is not the same as the country of approval, then the manufacturer's mark shall be preceded by the character(s) identifying the country of manufacture as indicated by the distinguishing signs of motor vehicles in international traffic. The country mark and the manufacturer’s mark shall be separated by a space or slash; The serial number assigned by the manufacturer; In the case of steel receptacles and composite receptacles with steel liner, the letter "H" showing compatibility of the steel (see 1SO 11114-1:1997); and, In the case of metal hydride storage systems having limited life, the date of expiry, denoted by the letters "FINAL" followed by the year (four digits) followed by the month (two digits) separated by a slash (i.e. "/"). Vehicle systems Irrespective of the guidance above, metal hydride storage systems intended for use in conveyances such as passenger vehicles or buses must also have the special approval of the authority having such jurisdiction in the country of shipment and receipt prior to shipment. Next steps Now that the UN Model Regulations provide coverage for hydrogen stored in metal hydride storage systems that conform to ISO 16111: 2008 and the requirements above, the various transportation modes (air, sea, road and rail) will be asked to adopt these same requirements as a matter of course.  It is expected that this will eventually result in harmonized regulations worldwide. For more information, please contact the US Fuel Cell Council Technical Director, Robert Wichert, at Wichert@usfcc.com.