Research and Teaching Activities

University of Alberta

Plasticity of Pipelines

adeeb@ualberta.ca

 

The development of high steel grades require revisiting the material models in plasticity to ensure that such high strength steel material still follow the traditional plasticity formulation. It has been shown that in high strength pipeline steels, the behaviour in the circumferential direction is different from the behaviour in the longitudinal direction. This can be attributed, among other reasons, to the forming process combined with the Bauschinger effect of the virgin materials.

The problem of the apparent orthotropic plasticity in pipeline steel has not been extensively studied. Most pipelines are designed for the circumferential stresses due to the internal pressure with very little concern for the longitudinal stresses. However, pipelines in the Northern regions pass through areas of discontinuous permafrost. In these areas, the seasonal freezing and thawing of certain parts along the path of the pipeline lead to differential settlement in the pipeline. This differential settlement will lead to additional substantial compressive bending stresses that need to be taken into consideration for the design of the pipeline. As the differential settlement is usually a displacement controlled process, pipeline companies are adopting strain based design methodologies in order to accurately predict the behaviour of their pipelines in the Northern regions. In order to adopt the strain based design methodology for such pipeline material accurate material modelling that reflects the three dimensional plastic strain state with respect to the three dimensional stress state that also include the cycling effects should be studied.

 

 Adeeb, S.; Zhou, J. and Horsley, D. (2006). Investigating the effect of UOE forming process on the buckling of line pipes using finite element modelling. Proceedings of IPC 2006. September 25-29, Calgary, Alberta. IPC2006-10175.

 

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