8.4　Piping for Steam and Water Systems

8.4.1　The piping support and hanger shall be installed in accordance with the following requirements:

1　The structures and installation positions of piping supports and hangers shall conform to the requirements of the design technical document.

2　The supports and hangers shall be firmly installed and tightly contacted with the pipes.

3　The hanger rods for pipes without thermal displacement shall be vertically installed.

4　As for the piping with thermal displacement，its hanging points shall be at the opposite direction of displacement and its displacement amount shall comply with the requirement of the design technical document.

5　The fixed supports shall be fastened prior to the pretensioning of compensator.

6　The guiding supports or the sliding support shall be free of deflection or jamming，and their sliding surface shall be cleaned up and their offset shall comply with the requirement of the design technical document.

7　The springs of the spring supports and hangers shall be precompressed as required by the design technical document and their height shall conform to the requirement of the document.

8.4.2　The pipes shall be installed according to the following requirements:

1　The straightness of butt joints shall be adjusted，and the measurement by ruler should be carried out at 200mm away from the center of the joints，with the allowable deviation of 2.0mm or 1.0mm respectively in case of pipe nominal diameter of not less than 100mm or that of less than 100mm.

2　The offset of internal wall of pipe butt joints should not be more than 10% of wall thickness and not more than 2.0mm.

3　The pipe shall be free of sundries inside and the area not less than 20mm away from the butt joints shall be free of oil，paint and any other dirt.

4　The butt welds of pipes shall be not less than 50mm away from the edge of their supports and hangers.

5　The valves shall be installed in accurate positions and directions and remain perpendicular to the center line of pipes.They shall be clean and firmly connected inside.

6　The compensator shall be installed in correct direction，pretensioned or compressed as required by the design technical document，remain concentric with pipes，and not be deflected.

7　The longitudinal and horizontal center lines of pipes shall be adjusted，and the measurement by ruler should be carried out，with the allowable deviation of 15.0mm.

8　The elevation shall be adjusted，and the measurement by optical instrument should be carried out，with the allowable deviation of±15.0mm.

9　The straightness of horizontal piping shall be adjusted，and the measurement by ruler and pulling wire should be carried out.In case of its nominal diameter not larger than 100mm，the allowable deviation shall be 2.0/1000 of effective length，the maximum being 50.0mm；in case of its nominal diameter larger than 100mm，the allowable deviation shall be 3.0/1000 of effective length，the maximum being 80.0mm.

10　The verticality of vertical pipes shall be adjusted，and the measurement by suspension wire should be carried out，with the allowable deviation of 5.0/1000 of effective length（the maximum being 30.0mm）.

11　The distance of pipes in a row shall be adjusted，and the measurement by ruler should be carried out，with the allowable deviation of 15.0mm.

12　The distance of cross pipes'external walls or heat-insulating layers shall be adjusted，and the measurement by ruler should be carried out，with the allowable deviation of 20.0mm.

8.4.3　Prior to piping welding，the corresponding WPQ shall be carried out and the operation instruction for welding shall be prepared based on the WPQ report.The welding shall be carried out in strict accordance with the instruction.

8.4.4　The quality，inspection method and inspection quantity of welds shall meet the requirement of the design technical document，or related requirement for boiler installation in the current national standards in case of no requirement in the design technical document.

8.4.5　The pipes shall be flushed according to the following requirements:

1　The pipes shall be flushed according to the situations of different systems.

2　The water for flushing shall be clean and with the flow of not less than 1.5m/s.The cross sectional area of discharge pipe must not be smaller than 60% of that of the pipe to be flushed.

3　The criterion for qualified flushing is that the color and transparency of water at the sewage outlet is consistent with that of water at the inlet via visual inspection.

4　After completion of flushing，the water shall be timely discharged，during of which must not result in negative pressure.