The Effects of Degree of Bending (DoB) in Multi-planar DTKY Tubular Joint on the Stress Concentration and Intensity Factors for Fatigue Assessment of Offshore Structures

Offshore platforms in Indonesia especially jacket platforms were operated over 20 years old. The jacket that has exceeded their operational lifetime needs to be reviewed in terms of structural strength and fatigue life to ensure ability for further operation. The estimation of fatigue life of the tubular using S–N curve approach considering hot spot stress (HSS) and stress occurred through the thickness of the joint’s tubular members, which can be indicated by degree of bending (DoB). It is important to evaluate the DoB effects on stress concentration factor (SCF) and stress intensity factor (SIF) of the joint. This research analyzed jacket structure with three types of multi-planar tubular joints, namely DTDY, DKDT, and DTKY. From the global in-place analysis, the largest unity checks of 0.56 occurred on the DTKY tubular joint as the critical joint. Finite element analysis then was carried out for the DTKY joint subjected of axial loading acting on the joint’s members. The analysis results that the critical member is Brace 3 of the joints with a maximum equivalent stress of 162.12 MPa. The location of the maximum stress then be used to extrapolate the HSS and calculate the DoB. The geometric parameters vary as β, γ, and τ to evaluate their effect on the DoB of the joint. The result shows that DoB value has a significant impact on the SCF and SIF that in turn can reduce the life of the jacket platform.