The Simulation Analysis On Fatigue Properties On Multi-planar Tubular Joints Weld For Offshore Platform

As a critical infrastructure in offshore exploration of energy resources, the structure of offshore platform is welded by numbers of cylindrical pipe components. Therefore, the distribution of stress at the weld toe of tubular joint inevitably exist concentration phenomenon. In the service period, the marine environment has a long-term influence on the offshore platform, and the tubular joint is peculiarly prone to fatigue damage, crack initiation, crack growth and fracture, which causes irreparable heavy casualties and economic losses. The tubular joint is the key part in offshore platform, and fatigue properties will directly affect the stability and security of offshore platforms. Therefore, it is of great significance to have the fatigue properties research on tubular joints weld for offshore platform. This paper uses the finite element technique and numerical analysis methods to do fundamental research on fatigue properties of tubular joint.Firstly, the loads on the marine environment (wind, currents and wave loads) are introduced comprehensively, and on the basis of this analysis, the simple mathematical models of load on the marine environment are established. As the object of the study, the jacket offshore platform is given the static analysis under the bad conditions and wave loads spectral analysis by ANSYS, and in this process, the place of the most dangerous multi-planar tubular joint is found. This makes a preparation for the next step of fatigue properties analysis.Secondly, follow the AWS welding specification, such the tubular DX-joint included the welding profile is modeled. Under of the different combined loads, the stress distribution of multi-planar tubular DX-joint along the weld toe is studied by the finite element method. The position of the hot-spot’s trend is explored in order to lay the foundation for preventing fatigue failure of the tubular joint.Last, according to the position of tubular DX-joint hot-spot under the different combined loads, the crack is created at the saddle of joint. To get the trend of stress intensity factors to multi-planar tubular DX-joint weld saddle point’s three-dimensional fatigue crack by aim of numerical analysis methods, it also provides a theoretical basis to promptly stop crack propagation.To further study the process of surface fatigue crack growth, and according to the analysis of Paris fatigue crack growth law, the T-butt joint included the surface crack at the weld toe is subjected to the axial load and moment load for numerical analysis of the crack propagation path and predicting the remaining life of the crack.This paper is to study the fatigue properties simulation analysis of multi-planar tubular joints weld for offshore platform. It provides a theoretical analysis method for the tubular joint safe service and basis for fatigue test analysis of platform multiplanar tubular test analysis at the next step.