5.2　Pipes

5.2.1　The pipe diameter shall be determined in accordance with 7.2 of this code.

5.2.2　The pipe strength shall be determined in accordance with 6.2.1 of this code.

5.2.3　For drain piping and recirculation piping carrying steam-water two-phase flow，the piping located downstream of the valve should be made of CrMo steel and the wall thickness should be one grade larger.

5.2.4　Seamless steel pipes in accordance with the current national standard GB/T 8163 Seamless Steel Tubes for Liquid Service can be used for the piping with a design pressure equal to or less than 1.6 MPa.Seamless steel pipes in accordance with the current national standard GB 3087 Seamless Steel Tubes for Low and Medium Pressure Boiler can be used for the piping with a design pressure equal to or less than 5.3 MPa.Seamless steel pipes in accordance with the current national standard GB 5310 Seamless Steel Tubes and Pipes for High Pressure Boiler can be used for the piping with a design pressure above 5.3 MPa.

5.2.5　Steel pipes and fittings with a longitudinal electric-fusion weld for high-pressure service at moderate or high temperatures can be used for the piping with a design pressure equal to or less than 10 MPa and a design temperature not fall within the creep range.Electric-fusion-welded steel pipes for low pressure fluid can be used for the piping with a design pressure equal to or less than 1.6 MPa and a design temperature equal to or lower than 300℃.

5.2.6　Welded steel pipes should not be used for low pressure feedwater piping.