Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Fatigue life prediction in rigid risers with crack propagation
Submission Author:
Andrielli Pereira , RJ
Co-Authors:
Andrielli Pereira, Gilberto Ellwanger, Jose Renato Mendes de Sousa, Silvia Corbani
Presenter: Andrielli Pereira
doi://10.26678/ABCM.COBEM2021.COB2021-1049
Abstract
Risers are subjected to cyclic and severe environmental loads throughout their service lives. Linear Elastic Fracture Mechanics concepts can be a valuable tool to ensure their safe operation and reduce the conservatism of their designs. This paper presents a methodology for fatigue analysis in rigid risers, including crack nucleation and surface crack propagation. Initially, the global model of the riser is considered with finite beam elements in Orcaflex software loaded to sea states with constant waves. The global fatigue life is determined using stresses, S-N curves, and the Palmgren-Miner rule. The propagation of a pre-existence surface crack at the first weld in the top region of the riser is evaluated by the automatic crack growth technique in FRANC3D software. The remote stresses of three-dimensional models with solid finite element (FE) are obtained from the global model. Stress Intensity Factors (SIF) are computed with the Integral-M method. According to design standards, Newman-Raju closed-form SIF expressions can also be evaluated. Three different cross-section geometries are analyzed with these two approaches. The numerical SIFs for a/t<0.5 are in satisfactory agreement with the Newman-Raju closed-form, but a significant conservatism is found for a/t higher than 0.5. For both approaches, crack front shape and fatigue life are compared.
Keywords
Fatigue Life, Fatigue crack propagation, Risers, Finite Element Model
