This study involves the numerical simulation of crack growth in girth welds of steel catenary risers under constant tension and cyclic bending. The modeling was carried out with the aid of a finite elements framework and a fracture mechanics program, which generates the initial crack and updates the model mesh according to the local energy release rate of the crack front nodes. The non-linear analysis comprises three-dimensional model mesh with solid elements, finite rotations, elastic-plastic behavior of the material and the linear theory of fracture mechanics. The numerical results were qualitatively compared with proposed fatigue curve of the British Standard International code.
One of the most efficient methods of pipeline installation is the reeling laying process that involve pipe onshore welding and pipeline bending over a rigid circular surface (reel) on the vessel. Subsequently, the pipeline is straightened and launched under tension into the sea. The straightening operation may not be required depending on the residual strain in the pipe after the bending phase. They have been successfully used by PETROBRAS in Brazil for installing pipelines up to 1,360 m (4,460 ft) water depth. However, when the steel catenary riser (SCR) concept is considered in conjunction with these methods, there is some scepticism regarding the impact in the fatigue performance of the pipe caused by possible changes in the material and geometrical properties occurred during installation. Consequently, large scope pipeline installation campaigns may require a second contract for SCR's installation using the J-lay method. The project is then penalized due to the attention required to manage the additional interfaces and the consequent impact in the overall pipeline project schedule and costs. Bending, unbending, and straightening processes as applied in the current vessels induce to the pipe bending-curvature histories into the plastic range of the material.
