Design principles and considerations for pressure vessel flanges

Thread Content

Design principles and considerations for pressure vessel flanges. Design principles for flanges: When designing gaskets, it is necessary to keep the load on the gaskets as low as possible； When designing bolts, the diameter of the bolt’s central circle should be kept as small as possible in order to achieve the lowest possible flange torque, in accordance with the \"minimum load\" principle. The proportions of the flange’s cone section and ring structure should be appropriate so that all parts of the flange can exert their full strength while ensuring sufficient stiffness, following the \"full stress\" principle ； Precautions: For the flanges used in the connection between container cylinders whose nominal diameter is based on the inner diameter, or in the connection between the cylinders and the end caps, it is advisable to select them in accordance with the current industry standards \"Flanges, Gaskets, and Fasteners for Pressure Vessels\" NB/T 47020–47027-2012. When the container cylinders are made of steel pipes, the flanges used for connecting these cylinders or for linking them to the end caps should be chosen in line with the current industry standard \"Steel Pipe Flanges\" HG/T 20592, specifically the PN series of standards ； Flanges used for the connection between container cylinders with nominal diameters expressed in imperial units (including those where copper tubes are used as the cylinder body), or for the connection between the cylinder body and the end cap, should be selected in accordance with the current industry standard \"Steel Pipe Flanges – Class Series, HG/T 20615\" and the current industry standard \"Large-Diameter Steel Pipe Flanges\", Class Series, HG/T 20623 ； For containers holding explosive media or media with moderate toxicity, the nominal pressure class of the container flange should be no less than 0.6 MPa; for containers holding media with extreme or high toxicity, or highly permeable media, the nominal pressure class of the container flange should be no less than 1.0 MPa ； For the calculation of the equipment flanges used to hold the tube sheets in U-tube and floating-head heat exchangers, the design pressure should be taken as the higher design pressure among the two flow paths, while the calculation temperature can be the respective design temperature. The design pressure and design temperature for the bolts and gaskets are determined based on the higher parameters of the two flow paths ； When calculating flanges in accordance with national standards, the inner diameter of the flange as well as the thicknesses of its larger and smaller ends must take into account the corrosion allowance. For wafer-type butt-welded flanges, when the thickness of the smaller end of the flange is greater than the thickness of the tube at the joint, the thickness of the tube should be used as the thickness of the smaller end in the calculations ； When the flanges of heat exchanger equipment are equipped with partition plates, the impact of these partition plates must be taken into account ； The flanges of equipment used in towers must take the effect of bending moments into account; the equivalent calculated pressure should be determined accordingly ； The thickness of the flange ring does not require consideration for corrosion allowance due to the medium; in the absence of appropriate anti-corrosion measures, the atmospheric environment can be taken into account ； For external pressure flanges with low design pressures, they can be designed based on internal pressure calculations; the bolt area only needs to be considered in its tightened state. If a flange is subjected to both internal and external pressures during operation, it must be designed separately for each type of pressure, meeting the requirements for both simultaneously ； For applications involving high temperatures and pressures, where leaks are not allowed and minimal disassembly is required, a flange connection type with welded ring gaskets for sealing the flanges is advisable ； For containers holding extremely and highly toxic hazardous media, moderately toxic hazardous media with high permeability, liquefied petroleum gas, as well as equipment flanges operating under low-temperature, high-temperature, and fatigue conditions, a necked butt-weld design is recommended