Issues with pipe wall thickness?
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Flanges are specified by PN, while seamless steel pipes have wall thickness grades – how should one choose the pipe flange PN that corresponds to the wall thickness of the pipe? Should I refer to the pipeline characteristic table, or some other specifications? What is the wall thickness? What is the pressure resistance? Does the pipe have these properties?
The wall thickness is calculated based on parameters such as the design temperature and pressure of the medium, as well as the diameter of the pipe material; for details, refer to Section 2 of Chapter 6 in GB 50316
Page 132 of the Fourth Edition of the Chemical Process Design Manual explains the definition of SCH. If your flange is a butt-welded flange, according to the flange marking specifications, it is necessary to indicate details such as the wall thickness of the pipes being joined. So the flange designation might be WN DN300 PN16 RF sch20, with the last part indicating the wall thickness class of the pipe joint. There is no direct relationship between PN and sch; both are pipe thicknesses calculated based on the pipe’s design temperature, design pressure, minimum elbow radius, and hydrostatic test pressure. The SCH grade is then selected based on the calculated thickness of the pipe.