ASME B31.3 requires leak testing of all piping systems other than Category D systems. For piping in Category D Fluid Service, the piping may (at the Owner's option) be put in service without a leak test and examined for leakage during the initial operation of the system. This is an initial service leak test. For all other piping, the following options are available:
• Hydrostatic test
• Pneumatic test
• Hydropneumatic test
• Alternative leak test
An alternative leak test is only permitted by ASME B31.3 when:
• Exposure of the piping to water via a hydrostatic test would damage the linings or internal insulation, or contaminate a process that would be hazardous, corrosive, or inoperative in the presence of moisture; and
• A pneumatic test is considered by the owner to entail an unacceptable risk due to the potential release of stored energy in the system (the danger of a pneumatic test increases with the pressure and contained volume); or
• A hydrostatic test or pneumatic test would present the danger of brittle fracture due to low metal temperature during the test
