【正文】 Pd1 Pa, MPa dynamical pressure at the initial end of the pipe Pd2 Pa, MPa dynamical pressure of the pipe end PO Pa, MPa stagnation pressure at the initial end of the pipe P1 Pa, MPa pressure at the initial end of the pipe P2 Pa, MPa pressure of the pipe end PC Pa, MPa critical pressure of the media inside the pipe Pd Pa, MPa critical dynamical pressure of the media inside the pipe α ratio of the pressure at the initial end of the pipe and the pressure at the end of the space αc ratio of the pressure at the initial end of the pipe and the critical pressure t ℃ design temperature or working temperature ter ℃ design installation temperature αb20 MPa minimal tensile strength of the steel products at 20℃ α 3 MPa minimal yield limit of the steel products at design temperature αt3 (%) MPa minimal yield limit when the steel products residual deformation is % at design temperature ? tD MPa 100, 000 h average endurable strength of the steel materials at design temperature 4 [? ]T MPa safe allowable stress of the steel products at design temperature ? safe allowable stress pensation factor DN mm inside nominal diameter DO mm pipe external diameter Di mm internal pipe size sm mm minimal straight pipe wall thickness SC mm calculated wall thickness of the straight pipe S mm wall thickness of the straight pipe A negative deviation coefficient of the pipe thickness G t/h media mass flow Gmax t/h media maximal mass flow Gmin t/h media minimal mass flow Q m3/h media volumetric flow v m3/kg media specific volume v0 m3/kg pipeline initial end stagnation specific volume v1 m3/kg media specific volume at the pipe initial v2 m3/kg media specific volume at the pipe terminal v m3/kg media critical specific volume β media specific volume ratio at the pipe terminal and initial end β0 ratio of media critical specific volume and pipeline initial media specific volume ρ kg/m3 media density Ρ1 kg/m3 media density at the pipeline initial Ρ2 kg/m3 media density at the pipe terminal w m/s media flow velocity m kg/(m2 when the pressure is lower than 3% of the nominal pressure, it will not be considered. The design pressure of the main pipe is applicable in the following specifications: (1) Main steam line Nominal working pressure at the boiler superheater exit or working pressure at the maximumcontinuous evaporative capacity of boiler shall be taken. When the boiler and steam turbine permits the pressure to be 5% greater (5% OP for short), 5% overpressure value shall be added. (2) Reheat steam pipeline The pressure shall be times of the pressure cylinder exhaust pressure under steam turbine39。s water inlet side pressure respectively。s interface section and it shall be no lower than 。s drainage pipe It shall be times of the extraction pressure under the steam turbine39。 for 11 pipeline after the stop valve, the constant voltage deoxidizing system shall take the rated pressure of the deaerator。s rated pressure shall be adopted. (13)Exhaust pipe after the safety valve It shall be determined according to the hydraulic calculation result of the blowdown pipe. Design temperature It refers to the maximal working temperature of the media inside the pipe. The design temperature for the main pipe shall be selected according to the following specifications: (1) Main steam line It shall take the steam39。s maximal design capacity operating condition。 12 Regulated extraction line takes the maximal working temperature of the exhaust gas. (4) Blowdown line of the backpressure steam turbine Steam exhaust39。s maximal design capacity operating condition shall be taken. (9) Condensate pipe Maximal working temperature of the condensation water after the low pressure heater shall be taken. (10) Drainage pipe of the heater The corresponding saturation temperature according to the heater extraction line39。s maximal design capacity operating condition shall be adopted. (13) Blowdown line of safety valve Design temperature for the blowdown line shall be selected from the corresponding statistics according to the blowdown line39。 it refers to the media volumetric flow safe allowable stress of the steel products at certain temperature, MPa. Nominal pressures for the general homemade steel products are listed in APPX ~. Water pressure test Water pressure test is used in testing the strength of pipe and its fittings as well as pipe system39。 Di Internal diameter of pipe, mm。 ? Compensation factor of the safe allowable stress。 MA Resultant moment on the pipe cross section for its self weight and other continuous external load, N otherwise, measures must be taken to prevent freezing and coldshort rupturing. Water used in the water pressure test must be clean and it must have very little corrosiveness on the pipe system. The austenitic stainless steel pipeline must adopt drinking water, and the chloride ion content shall be no greater than 25mg/L. Weld joints in the main steam line and reheat steam pipeline of subcritical units or units with the above stated parameters or other trunk main can also have tightness test by adopting nondestructive test in place of water pressure test. The requirements for nondestructive test shall be in pliance with the specifications in ―electric power construction and technical specification for the acceptance (radio examination of steel loadbearing pipeline buttjointed seam)。 δst Yield limit minimal value of the steel products at design temperature, MPa。 average rupture life at design temperature 105h, MPa. Data for the allowable stress of homemade steel products in mon use is listed in Annex . Data for the allowable stress of abroad steel products in mon use is listed in Annex 18 ,