Fatigue life estimation of tubular joints – a comparative study

Abstract

AbstractIn fatigue analysis, the structural detail of tubular joint has taken great attention among engineers. The DNV/GL‐RP‐0005 is covering this topic quite well for simple and clear joint cases. For complex joint and geometry, where joint classification is not available and there is limitation on validity range of non‐dimensional geometric parameters, the challenges become a fact among engineers. The classification of joint is an important factor to consider in fatigue analysis. These joint configurations are identified by the connectivity and the load distribution of tubular joints. To overcome these problems to some extent, this paper compares the fatigue life of tubular joints in offshore jacket according to the stress concentration factors (SCF) in DNV/GL‐RP‐0005 and finite element method employed in Abaqus/CAE. The paper presents the geometric details, material properties and load history of the considered jacket structure. It then describes the global structural analysis and identification of critical tubular joints for fatigue life estimation. Hence, fatigue life is determined based on the guidelines provided in design codes. Fatigue analysis of tubular joints is conducted using the finite element employed in Abaqus/CAE as the next major step. Finally, predicted SCFs and fatigue lives are compared, and these observations tend to conclude that even though the fatigue life, which is calculated based on code given SCFs, provides more realistic prediction to the simple uniplanar joints, there is a doubt for complex joints and geometry, where joint classification is not available. Also, the study emphasized that it is very important to preciously investigate SCFs by considering accurate geometry of complex tubular joints for a good judgement of fatigue life.