Bolting and loss of contact between cylindrical flat-flanged joints without gaskets

Abstract

Four bolts of a lightweight, steel, flanged joint were strain-gauged to measure bolt tension and bending. Three-dimensional, finite element analysis was used to determine bolt strains and gaps between the flanges due to axial tension and internal pressure for three different contact conditions. Two joints were tested. The front faces of the first joint were nominally flat while the second had a small negative cone angle (⋍ 0 degrees 15 minutes) so that flanges initially touched at the outside only. The non-linearity of experimental bolt strain with external load shows that the contact area around the bolts decreases with increasing axial tension. Comparison with the finite element predictions shows the rate at which the contact area diminishes. The finite element results also demonstrate that flange deflection is underestimated when contact area loss is ignored, and the consequences for leakage prediction are explained.