【正文】 A5 in Appendix A can be used to select material in case of no concrete requirement provided. Asbestos rubber pad should be soft and pliant, without any aging or delaminating。 Whether corrosion occurs on the valve stem wherever padding sealing。 water pressure method can be replace by oil or water peration method to perform tightness test for large caliber welding valve which inside nominal diameter is more than or equal to 600mm. Paint such as grease are strictly prohibited on the joint surface prior to the tightness test of valve. Method of water pressure tightness test must be in concordance with the requirement of valve 7 manufacturer. In the test, water should be filled in from the upstream of valve flap for shut off valve, and all sealing surface should be checked with valve closed for gate valve. All qualified valves should be kept well according to their classification after tightness test, and any water reminding in chamber must be remove pletely. Dismounting checking is necessary for following valves: Valve which designing temperature is more than or equal to 450℃ 。 Whether the joint between valve seat and valve case is firm, without loosen。 The contacting condition of valve cover flange surface。 Padding material should be filled correctly, and the inclined mouthpiece should be made, and mouthpiece of each layer should be staggered. Tightness must be ensured after the pactness of padding material and the motion of valve stem should not be hampered. Flow channel of valve of oil system should be cleaned to remove any molding sand, paint and etc, and oil proof packing set and shim should be replaced. When reassembling, screws of valve cover can only be fastened when valve flap is at opening position after the dismounting checking of gate valve and shut off valve has finished. Tightness test is required after the reassembly of valve. Dismounting test and tightness checking can only be omitted if manufacturer can provide the quality guarantee of products or qualified and operating certificate is provided, or check should be done according to the regulations in this chapter. For operating mechanism and drive mechanism, required check and adjustment must be carried out according to designing requirement, to make them act flexibly and indicate accurately. Preparation of pipes, pipe fittings and pipe accessories General regulations Preparation of pipe and the processing of supporting and suspending bracket should be in accordance with design drawings and relative regulations in standard. Materials and specifications of steel pipes, steel plates and other shaped steels should be in accordance with design requirement. Relevant regulations in active DL 5007 the Code of Erection and Acceptance for Electric Power Construction (Welding Section of Thermal Power Plant) must be observed when cutting pipe. Original marks should be transferred in time after high pressure steel pipe and alloy steel pipe had been cut off. Elbow pipe Pipe with positive tolerance of wall thickness should be adopted when pipe processing in case of no thickening pipe chosen. Bend radius of elbow pipe 39。 Allowable value of wave degree δ of bend section refers to Table . Allowable angle deviation is 177。 The out of roundness of straight section of bend pipe should be in accordance with technical requirement of steel pipe. Defect such as crack, deamination, burnt on surface are all forbidden after the bending of pipe. Nondestructive flaw detection is necessary in case 0 any doubt. Nondestructive flaw detection is necessary for high pressure pipe after bending, and the detection should be carried out were heat treatment is required for pipe which needs heat treatment. Grinding is possible in ease of defect, and wall thickness after grinding should not be less than the Min. thickness of strll1ght pipe. Metallurgical structure and hardness test must be done after the bending of alloy steel pipe and heat treatment, and the regulation of DL 438 Technology Supervision Regulation for Metal Parts in Thermal Power Plant must be observed. Quality certificate of product should be provided if qualified processing has finished for high pressure bend pipe. Processing of reel pipes, pipe fittings and pipe accessories All types of pipes should be prepared and processed according to the design drawings, and materials used should be in accordance with the design requirement. Corresponding active national or trade technical regulations must be observed for fed piece. Surface transition area between fed pipe fitting and pipe accessory should be roundness and smoothness. Defects on surface, which can affect strength and tightness, such as crack, is forbidden after machining. Defects such as missing welding, inplete fusion is prohibited for steel pipe, pipe fittings and pipe accessory that reeled by steel plate. Welding seam should pass the examining of kerosene peration test。 For deviation out of roundness, round template with inner arc equaling to 1/6 – 1/4 perimeter should be adopted for check, and clearance above 1 mm should not be allowable Deviation Δ f (see39。 Combination mode of miter elbow should be in accordance with design requirement, or it can be prepared according to the mode in figure . 10 Figure Miter elbow (a)90176。 miter elbow Additional intermediate join should be offered for elbow which inside nominal diameter is more than 400mm, while the Min. width of inner side should not be less than 5mm. Perimeter deviation of miter elbow should be in accordance with design requirement. And following should be observed in case of no design requirement provided: No more than 177。 Dimension of converging tube should be in accordance with following requirement: Diameter, out of roundness, verticality of end surface of b