6.2　Boiler Blowdown，Sampling，Heating，Drain and Discharge，Vent and Desuperheating Pipes

6.2.1　The erection of blowdown pipes and drain and discharge pipes shall meet the following requirements:

1　The pipe slope shall not be less than 0.2% under the operation condition.The pipes shall compensate freely and not affect the expansion of steam drums，headers and the piping system.

2　The blowdown pipes and drain and discharge pipes under different pressures shall not be connected with the same main pipe.

6.2.2　The periodic blowdown pipes shall be connected after the internal cleaning of waterwall headers.

6.2.3　The pressure grade of any drain and discharge pipe which can form the closed circuit during operation shall be the same as that of the connecting pipe.

6.2.4　The enough thermal compensation shall be provided for the erection of steam-water sampling pipe，and tube bundles shall be arranged orderly.

6.2.5　The expansion clearance shall be reserved for the erection of vent pipes.The supports and hangers shall be firm and stable.The load of the vent pipes shall not act on the valve or pipes.

6.2.6　The desuperheating water pipes and valves shall be arranged reasonably，with free expansion.The erection direction of the nozzle shall be correct.

6.2.7　The flushing and steam blowing of desuperheating water system shall be carried out before operation.