軟質全面形ガスケットを用いる全面座管フランジの基準寸法の妥当性に関する検討

抄録

Design of bolted flange connections has been performed for only raised face flanges based on stress evaluations on them. New design method taking consideration not only stress evaluations but also sealing ability of the flanges was introduced into the Japanese Industrial Standards (JIS). Sealing ability was examined in terms of the variation in gasket load witch resulted from deflection of flange rings under both gasket seating and pressurized conditions.
The maximum limiting pressures were calculated for each nominal size of steel full face flanges prescribed in JIS B 2220, by using above design method assuming soft full width gaskets. All variables in bolted flange connections, such as, dimensions and material properties of flanges, bolts and gaskets are included in the calculations.
Calculated results revealed that the dimensions of flanges of nominal sizes ranging from 10A to 225A were almost reasonable in the view point of the rating pressures prescribed in JIS of 7kgf/cm² (7kN/m²). In this range of nominal sizes, the calculated maxium limiting pressures increase with nominal sizes. There are some irregularities when bolt sizes or numbers of bolts change. In the flages of larger sizes than 250A, calculated maximum limiting pressures were far below the pressure required by JIS. Most of the limiting pressures for the flanges over 250A were limitied by the criterion of sealing ability because of low bending flexibility of the flanges, except the large size flange with extremely soft gasket, such as, rubber, in which stresses attain to the allowable stress under gasket seating condition
It is shown that the maximum limiting pressure increases when thickness of gasket increases because of large allowance in compressed deflection of gasket at gasket seating to recovery at pressurized. The same tendency is also estimated remarkably as soft gaskets, that is, gasket with low Young's modulus are used. The maximum limiting pressures are also estimated on aluminium full face flanges, assuming A5083 alloy of allowable stress of 7kgf/mm² (0.7MPa). The maximum limiting pressures, restricted by the criterion of sealing ability, on aluminium flanges with the identical dimensions to steel flanges decrease to 70% of those made of steel due to lower Young's modulus of aluminium alloy. In the case of stress limitation dominant, aluminium alloy flanges can be sustained to higher pressure than steel flanges due to short moment arms by larger flange ring deflection.