Abstract

AbstractThe use of steel catenary risers in offshore oil and gas production has increased significantly in recent years, in particular for deepwater applications. This paper presents a detailed assessment approach with respect to welded steel catenary risers, to reduce the requirement for over conservative factors of safety. The paper presents a global–local finite element modelling approach, with the Flexcom offshore dynamic analysis package used to determine the global load quantities for two ultra-deepwater free hanging steel catenary risers. These results act as stress boundary conditions in a local model using Abaqus, focusing on the failure susceptible regions of a girth weld. The methodology accounts for geometrical discontinuities of the weld and the different mechanical properties of the parent material, weld metal and heat affected zone, which result in fatigue hotspots for dynamic structures such as steel catenary risers. Two line pipe steels, a current generation X60 and a next generation X100, are investigated in the local analysis. Two pipe wall thicknesses are examined, with the weld geometry being different for each. It is shown that weld detail can lead to significantly different stress concentrations. X100 is shown to be superior to X60 with respect to yielding and fatigue.