Describes requirements for class I, class Ii and class III fusion welded steel air receivers, with following limitations : Class I: no limitation is placed on size or design pressure for receiver but requires non-destructive examination of all seams. Class II: design pressure shall not exceed 35 bar and product of design pressure (in bars) and internal diameter (in millimetres) shall not exceed 37,000. Class III: design pressure shall not exceed 17.5 bar and product of design pressure (in bars) and internal diameter (in millimetres) shall not exceed 8,800.