STRESS ANALYSIS OF BOLTED CONNECTION IN SPACE VEHICLES

Abstract

Pressure vessels are leak tight containers. They invariably have a flanged bolted connection at least on one end. Bolts apparently take tensile loads while the cylinder is subjected to internal pressure. However the flange has comparatively higher thickness than that of shell and has geometric discontinuity taking place at the flange-shell junction. Due to this the flange will be subjected to a shear force and a bending moment which are in turn resisted by the shell part. The bending moment and shear force even get transmitted to bolts. Hence instead of taking a pure tensile load, the bolts also take bending loads. A comprehensive design approach for this application is given in ASME Boiler and Pressure Vessel Code, Section VIII, Division 1. The corresponding British Standard, PD 5500:2000, and the new European Code, EN 13445, provide a less detailed design approach for these flanges, which ignores the influence of the shell. In this work, a beam theory is utilized to simplify an annular flange into a number of beams, so as to evaluate the bolt stress considering shell-flange interactions. Results obtained have been compared with an approximate analysis. The geometry considered is flat face flange with metal to metal contact outside the bolt circle. In this work the flange is treated as beam comprised of a series of radial beams. The analysis started with an approximation, before commencing detailed analysis. Followed by this the detailed analysis is carried out. From the analysis it has been observed that the contact circle radius increases reasonably as the pressure increases and correspondingly the stress also increases. The stress values agree well with the values of approximate analysis.