Fully plastic J and CTOD estimation procedure for circumferential surface cracks in biaxially loaded pipes.

• Ano de defesa: 2014
• Autor(a) principal: Parise, Luís Fernando Schiano
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Carregamento nas estruturas; Fracture mechanics; Loading on structures; Mecânica da fratura; Pipes; Tubulações
• Link de acesso: http://www.teses.usp.br/teses/disponiveis/3/3135/tde-14122014-171536/

The main goal of this work is to develop an estimation procedure for the and CTOD driving forces for circumferential surface cracks in pipelines under combined bending and internal pressure loading. It is intended that the methodology proposed here will be applicable to a significant range of pipe and crack geometries, material yielding and strain hardening characteristics as well as loading biaxiality levels. In particular, pipelines currently employed in the offshore oil and gas production industry constitute an important class of potential application for this kind of procedure, and thus the current structural integrity concerns involving the reeling of pressurized pipelines have served as a motivating theme and bridge with real-world application throughout this research. The central theoretical framework upon which the developments presented here are based is the driving force estimation scheme known as EPRI methodology. This traditional approach for estimating and CTOD relies on splitting the driving forces into elastic and plastic components. The elastic part is calculated directly from widely available stress intensity factor solutions, while the plastic part is determined using fully plastic solutions derived from power-law descriptions of material behaviour. In the first part of this work the EPRI methodology in its more conventional form is extended to cover the cases of interest, allowing the calculation of and CTOD for circumferential surface cracks in pipelines subjected to combined internal pressure and bending loadings. This is done by carrying out detailed finite element simulations of bending of pressurized cracked pipes, the results of which then allow the direct determination of non-dimensional functions that correlate (CTOD) with applied loading, consistent with the form of the original EPRI fully plastic solutions. In the second part of the work attention is given to certain drawbacks and limitations of the procedure developed in the first part. A new, alternative procedure is then proposed which aims to overcome these problems by combining the main ideas behind the EPRI methodology with concepts from strain based design. The theoretical framework underlying this development is laid out and the analytical derivation of the new driving force estimation scheme is presented. Finally, results are given in a form similar to that employed in the first part, and the two procedures are compared. While they are shown to be conceptually equivalent, the strain based methodology is argued to be more readily applicable to some important classes of real world problems. The work concludes with comments on the effects of load biaxiality over crack driving forces and with discussions on the quality, accuracy and physical meaningfulness of the non-dimensional scaling functions obtained which correlate crack driving forces to loads or strains.