Stress analysis of welded joints in internal stiffener rings in an aluminum cylinder

Abstract

Structural weight is one of the key criteria for vessels used in marine industries. The use of stiffeners and stringers strengthens the structure with the addition of a minimum weight. In cylindrical pressure vessels under hydrostatic pressure, mostly ring-type stiffeners are used. In order to join a stiffener ring to the vessel, welding is a conventional method. However, this process generates welding residual stresses and distortions, which can be added to external loads and cause structural failure. This study aims to develop a comprehensive simulation tool to predict distortions and residual stresses generated due to fillet-welded stiffener ring on an aluminum cylinder. Therefore, a hybrid numerical simulation approach has been employed. The simulation strategy has been implemented by using finite element software ANSYS enhanced with a number of subroutines. Results showed that the stiffener ring changes distortion trend in all orientation, especially in the radial direction with a reduction up to 15% in stiffener ring position. On the other hand, the radial residual stress was negligible and the hoop residual stress was tensile in the fillet weld region, with half of the base metal tensile strength magnitude, except in the start and the end of weld. Moreover, the axial residual stresses in the weld region on inner and outer surface of vessel in stiffener ring position were tensile and compressive, respectively.