VERIFICATION OF FLANGE RIGIDITY INDEX FOR STANDARD FLANGES USING FINITE ELEMENT ANALYSIS

摘要

A flange connection consists of the flange, gasket, bolts, and pipe. In a flange design stage, the flange rigidity index is checked to ensure the leak tightness of the flange connection. Technically, the flange rigidity index was theoretically derived by the function of flexure induced into the flange by both bolt tension and internal pressure. However, some of the factors used to calculate the flange rigidity index were determined by regression formulas. On the other hand, the rotation angle of the flange is also limited to determine the allowable boltpre-tension. To better understand the flange rigidity index, flange rigidity index and flange rotation angle were compared. The flange rotation angle was calculated using Finite Element Analysis (FEA). For the evaluation model, NPS3, 6,12,18, 24 for classes 150, 300, 600, 900,1500 integral-type flanges were selected. Typical gasket seating and operating conditions were considered in this study. In gasket seating condition, the required minimum bolt load was applied In operating condition, internal pressure and uniform temperature were simultaneously applied to the FEA model. From the analysis results, it was concluded that the specified flange rigidity indexes may underestimate the leak tightness for lower pressure and large flange types.