A Study of the Stress Intensity Factor and Crack Opening Displacement Relationship Between Uniform Thickness Pipe Bends and Non-Uniform Thickness Pipe Bends

Abstract

This paper proposes the relationship of stress intensity factor and crack opening displacement between pipe bends with uniform thickness and those with non-uniform thickness. In actual case, pipe bends have thickness variations. Unlike typical pipe bends, heat induction bend pipes have significant thickness variations (non-uniform thickness) because of manufacturing process. When the ratio of radius of curvature and pipe radius is 3 for heat induction bend pipes, the thickness at intrados and extrados can be calculated by 1.75 times and 0.875 times of nominal thickness which is original thickness before manufacturing process, respectively. In this situation, it is difficult to apply existing elastic stress intensity factor and crack opening displacement results [1, 2] and it is essential to modify existing solution or to create new solution. In this paper, to find effect of pipe bends thickness variation, 90° through-wall cracked pipe bends with not only uniform thickness but also non-uniform thickness are considered. The ratios of radius and thickness are 5, 10 and ratios of pipe radius of curvature and radius are 3, 4 and 5. Loading condition is in-plane opening bending for intrados crack and closing bending for extrados crack. The through-wall crack sizes are 12.5%, 25% and 37.5% of circumferential cross section. Material of pipe bends is assumed to follow elastic behavior. The proposal is made by extensive finite elements analyses using ABAQUS [3], predicted elastic stress intensity factors for pipe bends with non-uniform thickness are compared with finite element results. The results show a good agreement. It may be useful to calculate elastic stress intensity factor for bends with non-uniform thickness without complex modeling and finite analyses.