Antoon Lefevre

Effect of Pipe and Weld Metal Post-Yield Characteristics on Plastic Straining Capacity of Axially Loaded Pipelines

Girth welds in pipelines subject to longitudinal plastic tensile strains are critical regions of the pipeline. As girth welds might contain flaws of some form or other, it is of paramount interest to have a thorough understanding of the deformation characteristics of girth welds in the post-yield loading range. The response of a defective weld to plastic strains depends on many variables. While toughness is an important variable, large-scale tests demonstrate that the plastic straining capacity is directly affected by the mechanical properties of the materials surrounding the defect. The purpose of this paper is to describe the effect of the interrelation between the pipe and weld metal post-yield characteristics on the straining capacity of girth welds containing a defect.Copyright

Development of Defect Interaction Criteria for Pipeline Girth Welds Subjected to Plastic Collapse Conditions

Multiple defects in welds, when detected, have to be assessed for interaction. Current defect interaction rules are largely based on linear elastic fracture mechanics principles (brittle material behaviour). Pipeline welding codes, however, specify toughness requirements to ensure ductile failure by plastic collapse. Therefore, the use of current (elastic) interaction rules for ductile girth welds can lead to unnecessary and possibly harmful weld repairs or cutouts. This paper reports on an assessment of the engineering significance of existing pipeline specific interaction criteria and on the development of new criteria. Rules for the interaction of coplanar surface breaking defects and ductile material behaviour have been developed on the basis of the performance requirement of remote yielding. The results of large-scale tensile tests illustrate that current interaction rules have a high degree of conservatism for plastic collapse conditions. The test data have been used to demonstrate that the developed procedure can be safely used for ductile girth welds.Copyright

Fitness-for-Purpose Assessment of Misaligned Welds

Despite many years of research, an understanding of the effect of misalignment is far from complete. This study is focused on an experimental assessment of the interaction between high-low misalignment (hi-lo) and defect tolerance of girth welds subjected to remotely applied plastic strains. The paper highlights the beneficial effect of weld strength overmatch on straining capacity and inherent conservative assumptions made in a standard ECA analysis.