ABSTRACT:

This paper focuses on the characterization of the fracture performance of X100 material in transition temperature region using both experimental and numerical methods. The ductile fracture has been analyzed using tests on round notched bar specimens and standard fracture mechanics tests performed at room temperature. In previous publications the damage model Gurson-Tvergaard-Needleman (GTN) has been applied and verified by existing experimental data to describe ductile fracture behavior. The brittle fracture and the fracture in temperature transition region have been studied by means of deep and shallow notched SENB specimens at two different temperatures T=- 80°C and -40°C. Besides elastic-plastic analyses to quantify constraint levels for different initial crack configurations at the onset of cleavage fracture, the brittle failure has been described using modified Beremin model. The influence of the stable crack growth on the cleavage failure probability in temperature transition region has been captured by coupling the ductile fracture model (GTN) with the modified Beremin model. Finally, examples have been presented for the practical application of the numerical results on the fracture assessment of the flawed high-strength pipelines.

INTRODUCTION

The increasing exploration of natural gas resources in remote areas with harsh climate has lead to the development of linepipe steel grades, which should demonstrate sufficient strength and toughness properties also in low temperature regions under various loading conditions. Although the governing failure mechanisms for the steel material have been studied intensively over the last decades, there is still missing comprehension about the influence and contribution of different microstructure entities on the onset of ductile and brittle failure especially for the newly developed high-strength linpipe steel grades, such as X100 material. The experimental database comprised e.g. tests on round notched bar specimens and fracture mechanics tests covering a wide range of stress states.

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