Fracture response of pipelines subject to large plastic deformation under bending

• Published in: The International journal of pressure vessels and piping Vol. 82; no. 3; pp. 201 - 215
• Main Authors: Østby, Erling, Jayadevan, K.R., Thaulow, Christian
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.03.2005; Elsevier
• Subjects: Applied sciences; Biaxial loading; Exact sciences and technology; Limit design; Linepipes; Mechanical engineering. Machine design; Steel design; Steel tanks and pressure vessels; boiler manufacturing; Strain-based approach; Surface cracks; Strain-based approach; Biaxial loading; Limit design; Surface cracks; Linepipes; High strain; Surface crack; Structure integrity; Circumferential weld; Biaxial load; Numerical method; Traction; Finite element method; Crack opening displacement; Inelasticity; Plasticity; Bending; Crack tip; System identification; Large pipe; Rupture; Underwater pipeline; High pressure; Hardening material; Plastics; Internal pressure
• ISSN: 0308-0161; 1879-3541
• DOI: 10.1016/j.ijpvp.2004.08.012

Demand for long-distance offshore pipelines is steadily increasing. High internal pressure combined with bending/tension, accompanied by large plastic strains, along with the potential flaws in girth welds make the structural integrity of pipelines a formidable challenge. 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 under more realistic loading conditions. The evolution of CTOD of a pipeline segment with an external circumferential surface crack is investigated under pure bend loading as well as bending 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 that at moderate levels of CTOD, the allowable moment capacity of the pipe decreases significantly with increase in internal pressure. Further, the variation of CTOD with strain can be well approximated by a simple linear relationship.