Fatigue Crack Growth Analysis of Lap Joints in Deck Plates of Single-Deck Floating Roofs

Abstract

The single-deck floating roofs are used in large aboveground oil storage tanks. The deck plates of the roofs have 4. 5mm in thickness and are joined by continuous full-fillet welds on the upper side of lap plates. The deck plates are subjected to cyclic bending deformation due to wind load. This may lead to fatigue cracks at the lap welded joints. The cracks continue to grow in long time period. The oil will be spilled on the welded joints of the deck plates when the cracks penetrate. In this paper, the crack growth of the surface cracks in the lap joints is described. The stress intensity factors are analyzed using the Influence Function Method established by Shiratori, and the crack growth is based on the Paris law. The stress analysis of the virtual cracked surface in the uncracked lap welded joint is performed by the plane strain elastic FEA. The relations between the load amplitude and the fatigue life of crack penetration are obtained.