Numerical simulation of dynamic brittle fracture of pipeline steel subjected to DWTT using XFEM-based cohesive segment technique

Reza H Talemi

doi:10.3221/igf-esis.36.15

Abstract

In the past several numerical studies have addressed the ductile mode of fracture propagation. However, the brittle mode of pipeline failure has not received as much attention yet. The main objective of this study is to predict brittle fracture behaviour of API X70 pipeline steel by means of a numerical approach. To this end, the eXtended Finite Element Method (XFEM)-based cohesive segment technique is used to model Drop Weight Tear Test (DWTT) of X70 pipeline steel at -100°C. In this model the dynamic stress intensity factor and crack velocity are calculated at the crack tip at each step of crack propagation.

Highlights

C oncerns have been raised that leaks in a CO2 pipeline could escalate to brittle fracture crack propagation, due to the large temperature drop associated with the expansion of dense phase CO2 to ambient conditions [1]
Nonn et al [4] modelled the ductile fracture behaviour of API X65Q pipeline steels subjected to Drop Weight Tear Test (DWTT) using the GTN model
There are limited studies that focus on brittle fracture of the DWTT or Charpy V-Notch (CVN) impact tests at low temperatures

Summary

Introduction

C oncerns have been raised that leaks in a CO2 pipeline could escalate to brittle fracture crack propagation, due to the large temperature drop associated with the expansion of dense phase CO2 to ambient conditions [1]. Scheider et al [3] have simulated ductile dynamic fracture propagation using a numerical approach with application of damage mechanics models and a cohesive zone method They used the GTN model to simulate the DWTT with pressed notch and pre-fatigued crack. For instance Sainte Catherine et al [5] have developed the Beremin (1983) cleavage model to simulate CVN and Sub-Size CVN impact tests at low temperature (-90°C) From their study they found that the results showed a good transferability potential. A 2D finite element model was developed to represent the actual practice of DWTT To this end the XFEM-based cohesive segment technique was used to model dynamic brittle fracture behaviour of API X70 pipeline steel. After validation of the developed model against experimental observations, significant results from the simulation are presented and discussed

Objectives

Results

Conclusion