ABSTRACT

In this study, a numerical model for the fracture analysis of gas pipelines is developed. We propose a novel model for analysis of slow and fast rates of fatigue crack propagation. The boundary element method by taking the displacement correlation techniques is implemented to compute the stress intensity factor for an existing crack. The proposed model is based on the nonlinear finite element method as a strong computational tool which can be used for fracture and fatigue analyses in gas pipelines. A FORTRAN based finite element in-house code is developed and used in this study.

INTRODUCTION

Recently, the initiation and growth rate of crack propagation in both brittle and ductile materials in pipelines have received considerable attention. The ductile fracture is associated with a relatively large plastic zone at the tip of an existing crack while this zone is significantly small in brittle materials. It should be noted that the size of the plastic zone in a crack propagation analysis is proportional to the initial and current length of an existing crack. The failure mechanism always starts with slow-rate crack propagation and ends with a catastrophic failure when the crack propagation rate is significantly high.

Developing a numerical model in order to estimate the crack growth rate in pressurized pipelines (for a dynamic internal pressure) is of crucial importance. In fact, any fatigue issues or catastrophic failures in a pipeline structure is because of the existence of small micro-cracks in the system (due to manufacturing cares, etc.). In order to control the crack growth rate, normally materials with improved physical and mechanical properties and better resistance to brittle fracture can be used. However environmental factors such as ground and ambient temperatures, humidity, and operating loads also play important roles in crack initiation and growth stages. [1,2].

This content is only available via PDF.
You can access this article if you purchase or spend a download.