Numerical Investigation on 3-D Two Collinear Cracks in Offshore Pipelines Under Bending

Under complicated loading conditions, small yet closely located cracks can grow and coalesce into a large crack which may pose a significant threat to the reliability of marine structures. A lot of research work has been carried out for the investigation of multiple cracks’ stress intensity factors and estimation of fatigue growth of multiple cracks. However, there is a lack of information on nonlinear elastic plastic analysis on fracture behavior of ductile materials.In this study, 3-D finite element analyses are conducted on offshore pipelines with two collinear cracks (a semi-elliptical surface crack and an elliptical embedded crack). The nonlinear elastic-plastic investigations are performed on fracture behaviors of these two interacting cracks subjected to large plastic strains. A comparison of fracture response (in terms of CTOD value) has been made between the current numerical results and the computational outcomes derived from BS7910: 2005. Last but not least, strain-based CTOD estimation formulas are proposed for assessing the fracture response of flawed pipelines with two collinear cracks under large plastic strain conditions.Copyright © 2015 by ASME