Assembly stresses and deflection of conical-faced flanges without gaskets

Abstract If the front and back faces of a pair of flanges are conical, continuous contact of the joint faces is achieved on assembly. This does not occur in flat flanges. However, high stresses may occur in the flanges because sufficient bolt load must be applied before the joint closes, so that sealing can be maintained under operating loads. Bending of the bolts may also occur on assembly. Sixteen tests were carried out on 7 different flange pairs having internal diameters of 147, 457 and 688 mm and cone angles of 2–6°, tightened by 8–48 bolts. Stresses in a 457 mm diameter flange pair were also investigated using the finite element method; an axisymmetric model was used. Bolt strains were obtained experimentally and closure loads were determined by analysis and experiment. Comparison of the axisymmetric finite element analysis of the 457 mm diameter flanges with experimental data shows that the flange flexibilities are accurately predicted for flanges having more than 24 bolts. For practical cone angles, the flexibility is independent of the cone angle. Bolt bending only occurs during tightening. However, the bending is insignificant at the rated torque, at which it was found that the effective line of action of the bolt load was inside the pitch circle of the bolt holes.