【正文】 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。 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。 Allowable value of wave degree δ of bend section refers to Table . Allowable angle deviation is 177。 The contacting condition of valve cover flange surface。 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℃ 。 Nondestructive flaw detection results of high pressure pipe fittings. Sealing surface of flange should be smooth and clean without radial groove, and air cavity, crack, burr or other defects that can reduce strength and connecting reliability are forbidden. Flanges with concave/convex surface or concave/convex ring should be snapped naturally, and the height of concave surface should not be less than the depth of notch. Supporting area of connecting bolts on flange end face should be parallel to the junction surface of flange, to insure even force acted on flange end surface when connecting. Dimensions of each part should be checked according to the design drawing and examined to determinate its conformity with flange on device to be connected, to ensure proper connection. Checking of pipe accessories Thread of bolts and nuts should Be undamaged without any defects such as scratches, burrs and etc. and the matching between bolt and nut should be in good condition without loosen or blocking. Each alloy steel bolt, which designing temperature is above 430 oC, and diameter is more than or equal to M30, should be numbered and its hardness should be checked, and unqualified one must not be used. Pad material of flange should be in concordance with the designing requirement. Table 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。 Water, power and pressed air used in construction sho uld satisfy the demands of construction. Active national or trade (or special) technical standards must be plied for the manufacturing quality and choosing of pipes, pipe fittings and pipe accessories. Active SDJ68 the Maintenance and Keeping Regulation for Electric Power Basic Construction Thermal Power Devices and corresponding additional regulations should be observed for the store of all types of pipes, pipe fittings and pipe accessories. All types of pipe should be constructed according to the design drawings, and it should be submitted t designing unit to treat in term of relevant regulation if the design should be modified or substitute material should be adopted. The relevant regulation in active DL 5007 the Code of Erection and Acceptance for Electric Power Construction (Welding Section of Thermal Power Plant) should also be observed in the cutting and welding operation f pipes construction besides the relevant regulations in this code. Regulations in SDJ 245 the Code of Erection and Acceptance for Electric Power Construction (Boiler Unit Set Section) should be plied 1ir the heat preservation and painting of pipes. And the painting of pipe should be carried out according to the regulation of DL 50I I the Code of Erection and Acceptance for Electric Power Construction (Steam Turbine Unit Set Section). Relevant regulations of active DL the Safety Operating Regulation of Electric Power Construction (Thermal Power Plant Section) must be observed for the safety, environment and fire protection in the piping construction of electric power plant. 5 Glossary Pipe fittings the general designation of parts and elements which posing piping system with pipes together, including elbow, elbow pipe, tee pipe, converging tube, pipe connecting saddle, flange, dead end, end plate and etc. Pipe accessories external supporting parts of piping system, including supporting and suspending bracket, shim, sealing parts, fastening parts and so on. Elbow piperefers to the pipe with bending axial line. Elbow refers to the elbow pipe which bending radius is no more than 2D, and straight section is less than 10. Miter elbow elbow made up of two or more straight pipe sections which welding together in the plane of equal bend angle (also called welding elbow or shrimp elbow). Calculation wall thickness of straight pipe the Min. wall thickness of straight pipe plus the negative deviation value of the wall thickness of straight pipe. Monitoring section pipe section used to monitor creep, which installed on horizontal section of main steam .pipes that designing temperature is above 4500C, or reheating high temperature steam pipes. Creeping expansion measuring point equipmen