【正文】 . Weld The selection of welding electrode and welding wire shall be based on the chemical position, mechanical property and crack resistance, carbon diffusion, weld preheating, postweld heat treatment of the welded joint as well as operating conditions of the base material. When steel products of the same kind are welded, adoption of the welding electrode (welding wire) shall be in pliance with the following requirements: (1) Performance and chemical position of the weld metal shall be equivalent to the base material. (2) Good processing property. When steel products of different kinds are welded, adoption of the welding electrode (welding wire) shall be in pliance with the following requirements: (1) For steel products with neither side as austenitic stainless steel, welding electrode (welding wire) that is between the two in terms of posite or the ones that is suitable to the side with lower alloy content can be adopted. (2) For steel with one side as austenitic stainless steel, chromiumnickel stainless steel or nickel base alloy covered electrode (welding wire) can be adopted. Types and performance of the steel welding electrodes in mon use (1) Type of the carbon steel covered electrode see annex . (2). Type of the low alloy structural steel see annex . (3) Types and chemical position of the welding wire in mon use see Annex . (4) Chemical position and mechanical property at ambient temperature of welding electrode‘s deposited metal in mon use see Annex . (5) Commendatory values for welding electrode (welding wire) to weld heterogeneous steel and postweld heat treatment temperature see Annex . (6) Applicable welding electrode and welding wire types for homemade steel products in mon use see Annex . 19 (7) Applicable welding electrode and welding wire types for abroad steel products in mon use see annex and annex . Fundamental form and dimension of welded joint in mon use see Annex . Processing method of contraaperture for dissimilar thickness see Annex . 3 Selections of pipes Pipe diameter selection Diameter sizes of the main ducts like main steam line, reheat steam pipeline and high pressure feed water pipeline shall be determined according to the optimization calculation. Pipeline of the monophasic fluid shall be calculated according to the equation below with the remendatory media velocity of flow: wGuD ?() Or wQD ?() Where iD inner diameter of the pipe, mm。 Q Volumetric flow of the media, m3/h For pipelines of aerated water twophase fluid (like high pressure heater drainage, boiler blowdown, and so on), pipe diameter or its swallowing capacity shall be calculated according to calculation method of twophase fluid pipe. Flow velocity of media in the aerated water pipe shall be selected according to . Table Commendatory pipe media flow speeds (m/s) Media Pipeline name Commendatory flow 20 category velocity draught (m/s) Main steam Main steam line 40~60 Reheat steam High temperature reheat pipe 50~65 Lowtemperature reheat pipe 30~45 Other steam Extraction or supplementary steam pipe: overheat steam, Saturated vapor, Warmup steam 30~60 30~50 20~35 Steam pipe leading to pressure reducer and attemperator 60~90 Feedwater High pressure feed water pipeline 2~6 Low voltage feedwater piping ~ Condensation Water Pipeline at the downstream side of the condensate pump ~ Pipeline at the inlet side of the condensate pump ~ Heater drainage Heater drainage pipeline : Drainage pump downstream side Drainage pump inlet side Adjusting valve downstream side Adjusting valve inlet side ~ ~ 20~100 1~2 Other water Raw water, chemical water, service water and other water conduits : Centrifugal pump outlet pipe and other pressure pipes Centrifugal pump inlet pipe Gravity flow and overflowing nonpressure drainage pipeline 2~3 ~ 1 During the selection of specific flow velocity wit。 U Specific volume of media, m3/kg。 residual deformation is %, MPa。 related strength property: δ b20/3, δst/ or δs(%)t/, δDt/ Thereinto, δ b20 Minimal value of the steel products39。 W Pipe39。 yield limit under test temperature. Axial stress shall be calculated according to: Where: L? The sum of the test pressure, self weight and the axial stress generated from other 16 continuous loads, MPa。 a The extra thickness required due to the consideration of erosion, abrasion and mechanical strength。 15 P – Design pressure, MPa。s nominal pressure The allowable working pressure and nominal pressure of the pipes and fittings can be converted as the equation below: ［ｐ］＝ PN xt][ ][ δ δ () Where: [p] The allowable working pressure, MPa。s rated pressure shall be adopted。s maximal working temperature at the temperature reducing device outlet shall be taken. (6) Aerated water pipeline connected to the monopipe boiler starting vessel The maximal possible working temperature that the pipeline can have during all segregator operation conditions shall be taken. (7) High pressure feed water pipeline The maximal working temperature of the high pressure feed water after using the high pressure heater. (8) Low voltage feedwater piping For the constant voltage deaerator system, the corresponding saturation temperature of the deaerator39。s extraction line Nonregulated extraction line take the extraction steam parameter under the steam turbine39。s normal operation. Suggested temperature deviation is 5℃ . (2) Reheat steam pipeline High temperature reheat pipe shall take the steam rated working temperature at the boiler reheater outlet plus the allowable temperature deviation during the boiler39。s heatup extraction pressure at the maximal design capacity operating condition of the steam turbine. When the pipingm