5.5　Flanges

5.5.1　Selection of flanges shall give due consideration to the influence of flange rigidity on the sealing performance of flange joints and also comply with the following requirements:

1　Applicable pressure and temperature of flanges shall meet the requirements on pressure-temperature rating in current national standard GB/T 9124 Specification for Steel Pipe Flanges.

2　If flanges with different pressure ratings are to be connected，flanges with a lower pressure rating shall meet the requirements for specific applications.

5.5.2　Selection of piping flanges shall comply with the following requirements as well as the provisions in the current national standard GB/T 9115 Steel Pipe Welding Neck Flanges.

1　For the piping with a design temperature above 300℃or the piping with PN≥40，butt welding flanges shall be used.For the piping with a design temperature of 300℃and PN≤25，slip-on flanges should be used.

2　In the piping system，plate type flat welding flange，socket-welding flanges，lap joint flanges and threaded flanges shall not be used.

5.5.3　With respect to flange facings，raised face（RF）and male and female face（MF）shall be used in accordance with the following requirements:

1　For butt welding flanges，MF and RF should be used.

2　For slip-on flanges，RF shall be used.

5.5.4　If special flanges are needed，the dimensions of flanged connections shall be checked and the compressive strength shall be calculated so as to ensure that the thickness of the selected flange is not less than that value specified in applicable national standard for the connected piping under nominal pressure.Calculation of flanges and flange connections shall comply with the provisions in 6.6 of this code.