Abstract: The layout form of the steam discharging pipe and the discharge process were introduced. The thermodynamic calculation methods of opentype and closedtype discharge systems were expounded emphatically. Based on the calculation method recommended in ASME B31.1, the methods specified in code for piping design of steam turbine were adopted to solve the critical mass volume ratio. The combining of the two calculation methods can give high calculation accuracy, better operability and obvious effects in practical application.

Key words: safety valve discharging pipe, discharge system, thermodynamic calculation, prevention of reverse spray