Presents data relative to the fabrication requirements for 2-1/4 3Cr alloy steel heavy wall pressure vessels for high temperature, high pressure hydrogen services. It summarizes the results of industry experience experimentation, and testing conducted by independent manufacturers, fabricators, ands users of heavy wall pressure vessels. This recommended practice applies to equipment in refineries, petrochemical, and chemical facilities in which hydrogen or hydrogen containing fluids are processed at elevated temperature and pressure.