Fracture response of pipelines subjected to large plastic deformation under tension

Abstract Economical design with sufficient fracture resistance is of utmost importance in any offshore pipeline project. High internal pressure combined with bending/tension, accompanied by large plastic strains, becomes a major design challenge for ensuring line integrity. Recent research efforts have pushed the design strain limits in compression to quite large values, but on the tension side, the limits are still very restrictive. The existing procedures for the fracture assessment of pipelines are based on simplified analytical methods and, these are derived for a load-based approach. Hence, application to surface cracked pipes under large deformation is doubtful. The aim of this paper is to understand and identify various parameters that influence the fracture response of cracks in pipelines. The evolution of CTOD of a line-pipe segment with an external circumferential surface crack is investigated under pure tensile loading as well as tension with internal pressure. Detailed 3D elastic–plastic finite element simulations are performed. The effects of crack depth, crack length, radius-to-thickness ratio and material hardening on fracture response are examined. The results show a significant enhancement of applied CTOD with increase in magnitude of internal pressure. Further, the variation of applied CTOD with strain can be well approximated by a simple linear relationship.

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