【正文】 4mm in case of DN≤ 1000mm。6mm in case of DN 1000mm。 miter elbow (d)30176。 miter elbow (b)60176。 Less than 3% outer diameter for medium/low pressure pipe。 figure ) of verticality of pipe end surface should not b more than the specified value in Table . Figure Diagram of the verticality deviation of pipe end surface Mechanical damage on pate surface should be avoided during the processing of reel pipe, and place with serious scratch must be ground, and transition area should be roundness and smoothness. Ground depth of pressure pipe should exceed 10% of plate thickness, and the wall thickness after ground should not be less than the Min. thickness of straight pipe. Plane deviation P and end surface deviation Q of all type of elbow should not be more than the specified values in Table (see figure ). Out of roundness of pushed elbow and pressed elbow should be in accordance with following demands in case of no design requirement provided: End: less than 1% outer diameter of pipe and no more than 3mm。40mm。 and nondestructive flaw detection is required for pressure pipe according to relative stipulations. 9 Following requirements should meet for steel pipe reeled by steel plate: Longitudinal welding seams should be staggered (no less than 100mm) for the butt joint of pipe sections。 True wall thickness of outer arc section of bend pipe should not be less than the Min. wall thickness of straight pipe。176。 7% for medium and low pressure pipe。must be in accordance with design requirement. Corresponding regulations in trade standard DL/T 515 Elbow Pipe Used in Power Station must be observed if no design requirement given for the Min. bend radius of elbow pipe. 8 Following regulations most be observed when elbow pipe is heated with medium frequency method: The heating temperature should be 8501000C when low carbon steel is bent. Water injection cooling can be adopted in case of pipe wall thickness is no more than 25mm, otherwise, forced air cooling should be adopted, and heat treatment is not necessary. Heating temperature of back arc of pipe must not exceed 90039。 Specification and quality of each pad and padding material should be in concordance with technical requirement。 Opening/closing stroke and end position must be checked for throttle valve, and mark should be made as far as possible. Following quality requirements should be satisfied after the dismounting checking and eliminating defects had been finished: Material of alloy steel should meet the requirement of design。 Whether the valve is bend and corrosion, and the tightness degree of matching between valve stem and padding material cover is suitable, and there are some defects such as broken thread on the thread of valve stem。 Whether the joint surface between valve stem and. valve seat is coincide, and without defects。 dismounting order specified by manufacturer must be observed when valve with special structure is been dismounted, to avoid damaging parts or hampering personnel safety. Following checking is necessary for valve dismounted: Spectrum rechecking should be carried out for interior parts of alloy steel valve (no marks noted on parts is allowed, while check results must be recorded)。 Safety valve and throttle valve。 additional 20% should be checked by sampling in case of someone is unqualified, and if someone does still not pass, all valves should be checked one by one. Tightness test must be done one by one for all valves used on high pressure pipe. Tightness test of sealing surface of valve core can be carried out with color painting method for safety valves and valves which nominal pressure no more than MPa and inside nominal diameter no less than 800mm。 If the action of switches are flexible and the indications are all correct。s. Radial scratch, loosen and other defects are all not allowed for the cladding metal and winding shim. Assembling dimension and welding type of steel structure of pipe supporting and suspending bracket should be concordance with the regulation of the code . Working surface of sliding bracket should be smooth and move flexibly without any blocking. Spring of pipe supporting and suspending bracket should be checked according to the article and of the code. Checking of valves Following examining is necessary prior to the installation of all types of valves: If padding material is in concordance with the requirement of design, and if padding method is correct or not. Sealing padding material can be selected according to the Table A6 in Appendix A in case of no design requirement provided。 and any defect such as buckle and wrinkle is forbidden on surface. Visual inspection should be made for the surface of metal shim with leveling rule, the good contact is necessary and defects such as crack, burr, rust or coarse processing are not allowed。 Heat treatment condition or metallurgical phase analysis results of alloy steel pipes。 Heat treatment condition or metallurgical phase analysis results of alloy steel pipes. Welding seam checking report must be examined prior to the using of seamed pipe which designing pressure is more than MPa. 6 Local defects such as scratches, concave cavities and corrodes on pipe surface should be checked。 Test results of mechanical property (tensile strength, yield strength and ratio of elongation)。 The surface should be smoothness without any sharp scratches。 Construction should satisfy the demands of environment。 Real technology munication and required technical training and examining should have 4 been finished。 Oxygen and acetylene pipes. Except the sections with other concrete stipulations in construction contract, the provisions in this code must be observed in the construction and acceptance of pipes of imported thermoelectric generating set. The piping i