A simplified procedure to prediction of ductile failure modes of a SA333 Gr.6 carbon steel pipe: Fracture instability and Plastic collapse condition

Abstract

Abstract Ductile failure assessments of circumferentially through walled cracked piping system are an important phenomenon for safety analysis of nuclear power plant. The present work is focused in this direction. The common failure modes of failure of components made of ductile materials are fracture instability (uncontrolled crack growth) and plastic collapse. In the current study, both the failure modes are considered in failure assessment of primary heat transport pipe of PHWR. The material of the piping system is SA333 Gr.6 carbon steel which has a large extent of ductility and thereby, the chances of plastic collapse are observed in certain conditions. The material J-R curve (J - Δa curve) for the material SA 333 carbon steel is determined using a CT specimen. A simplified method for determination of J – R curve is proposed. It is found that the J-R curve obtained by the proposed method is suitable for steady crack growth conditions and thereby, suitable for pipe fracture analysis where the extent of crack growth is large. Straight pipe with different crack angles are modeled in FE analysis under pure bending load. Applied moment versus J (Japp) curve is obtained from FE analysis for different crack angles. J is calculated using 3D version of Rice’s J-integral using domain integration method. Finally instability diagram for pipe is constructed using applied “Japp” vs semi crack angle with applied moments as parameters. Material J-R curve for the material SA333 Gr.6 carbon steel, determined by using CT specimen, is superimposed in this diagram to find the instability condition. This diagram also shows the condition of plastic collapse. Finally a failure chart is tabulated for various initial crack angles and applied moments.