Mechanical properties of buckled pipe materials

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The in-service mechanical buckling of pipelines is an important technological problem. The pipeline can experience complex loading paths after construction due to seismic events, soil shifting due to melting of permafrost or even the movement of heavy equipment over the buried pipeline. Thus, it is necessary to have models to predict the material behaviour of the pipe in service, such as the yield stress and the initial working hardening behaviour. Here, there are several important metallurgical phenomena which are relevant. First, it is qualitatively known that when the direction of the loading changes, this can affect the yield stress (classically known as the Bauschinger effect). In this case, the relevant scenario would be that the direction of deformation during forming the pipe can be orthogonal to bending strains that the pipe experiences in-service. Second, it is also known that the after plastic deformation and a static period at ambient temperatures, a "yield point" can be produced due to segregation of carbon atoms to crystal dislocations. However, there is a lack of knowledge on the basic mechanisms and the ability to predict this behaviour is limited to qualitative values.