GB/T 9124.1-2019Steel pipe flanges -- Part 1: PN designated (English PDF)

3.1 Nominal pressure

3.1.1 The definition of nominal pressure is given in GB/T 1048.

3.1.2 This Part specifies the following 12 pressure ratings, identified by PN, for nominal

pressure.

PN2.5, PN6, PN10, PN16, PN25, PN40, PN63, PN100, PN160, PN250, PN320, PN400.

3.2 Nominal size

3.2.1 The definition of nominal size is given in GB/T 1047.

3.2.2 This Part specifies the following 39 sizes, identified by DN, for nominal size.

DN10, DN15, DN20, DN25, DN32, DN40, DN50, DN65, DN80, DN100, DN125,

DN150, DN200, DN250, DN300, DN350, DN400, DN450, DN500, DN600, DN700,

DN800, DN900, DN1000, DN1200, DN1400, DN1600, DN1800, DN2000, DN2200,

DN2400, DN2600, DN2800, DN3000, DN3200, DN3400, DN3600, DN3800, DN4000.

5.1 Materials

5.1.1 Commonly used materials for steel pipe flanges shall conform to the provisions

of Table 92.The chemical composition, mechanical properties, operating temperature

and other technical requirements of flange materials shall comply with the relevant

standards in Table 92.

5.1.2 For the grades and technical requirements of forgings for pipe flanges (including

forged and rolled parts), refer to NB/T 47008 ~ NB/T 47010, which shall comply with

the following provisions.

a) For flanges with nominal pressure of PN2.5 ~ PN16, use low carbon steel and

austenitic stainless-steel forgings, where Class I forgings are permitted.

b) Forgings for flanges shall meet the requirements of Class III or higher forgings

if any of the following conditions are met.

1) Forgings for flanges with a nominal pressure greater than or equal to

PN100;

2) Chromium-molybdenum steel forgings for flanges with a nominal

pressure greater than or equal to PN63;

3) Ferritic steel forgings for flanges with a nominal pressure greater than or

equal to PN63 and an operating temperature less than or equal to -20 degrees C.

c) Other forgings for flanges shall meet the requirements of Class II or higher

forgings.

5.1.3 This Part does not cover the selection criteria for flange materials. Users shall

consider the possibility that the performance of the materials may deteriorate during

actual use. Users shall pay attention to issues such as the transformation of carbide

phases into graphite, excessive oxidation of ferrite materials, and the sensitivity of

austenitic materials to intergranular corrosion.

5.1.4 When the usage conditions impose certain specific requirements on the material,

such as requiring specific heat treatment, the user shall specify this in the order contract.

See Appendix D for flange order contract data.

5.1.5 The mechanical properties of the material shall be obtained from test samples

representing the final heat-treated state of the material.

5.2 Pressure-temperature ratings

5.2.1 The flange pressure-temperature rating shall conform to the provisions of Tables

5.2.2 Determine the maximum allowable working pressure of different materials at

different operating temperatures based on the pressure-temperature rating. For

intermediate temperatures, the maximum allowable working pressure of the flange at

that temperature can be determined by linear interpolation. For special materials, the

pressure-temperature rating shall be determined according to the design specifications.

5.2.3 If the pressure-temperature ratings of the two flanges in a pair of flange joints are

not the same, the pressure-temperature rating of the pair of flanges shall be determined

by the lower of the two flanges.

5.2.4 A flange joint is assembled from three separate, independent, yet interconnected

components. a flange, a gasket, and fasteners. Flange joints are also affected by the

assembly process. Strict control shall be exercised when selecting these components to

ensure that the flange joint has good sealing performance. To ensure good sealing

performance in flange joints, special techniques are required, such as controlling the

preload of fasteners.

5.2.5 The maximum allowable working pressure of the flange at low temperature shall

not exceed the maximum allowable working pressure at normal temperature.

5.2.6 For flanges used in high or low temperature environments, the risk of flange

leakage caused by the forces and torques generated by temperature changes in the

connected pipes and equipment shall be considered. For flanges used at high

temperatures, as the operating temperature increases, the flange, bolts, and gaskets will

gradually loosen, the bolt load will gradually decrease, and the sealing performance of

the flange will gradually decline accordingly. For flanges used at low temperatures,

especially some carbon steel flanges, their toughness is significantly reduced. In this

case, the flange may not be able to safely withstand impact loads, stress and temperature

changes, or it may generate high stress concentration. Therefore, it is required to test

the impact performance of materials at low temperatures according to relevant

standards to ensure the safe use of flanges at low temperatures.

5.2.7 The method for determining the pressure-temperature ratings is given in Appendix

E.

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