Structural mechanics of steel offshore pipelines

The installation of deep-water hydrocarbon offshore pipelines (in depths that exceed 2,000 meters) constitutes a critical stage in pipeline design. Among other methods, reeling is an efficient method for deep offshore installation of pipelines with diameter less than 16-inch; however, prior to water installation, the pipe is subjected to severe cyclic plastic deformations, well into the inelastic range of steel material. Subsequently, the pipe is subjected to a combination of external pressure and bending that may cause buckling, in the form of collapse, with catastrophic consequences; at that stage, pipeline ovality is a crucial design parameter, which is significantly affected by the previous cycles of inelastic bending.

Motivated by pipe response during reeling, the present PhD research focuses on the mechanical response of pipelines, subjected to plastic bending. Previous studies have shown that existing computational tools may not be capable of predicting the ovality induced by reeling, and this is due to the shape of the yield surface of a pipe material, which may change during reeling, and may not be captured in standard material models. However, more research is necessary.

The present PhD research is aimed at developing efficient numerical (finite element) tools that predict the mechanical response of steel pipes in the course of deep-water reeling installation. Among other issues, the development and calibration of an efficient constitutive model that accounts for the evolution of the yield surface with respect to plastic deformation is a target. The constitutive model will be incorporated in the finite element model, as a Material User subroutine.

The research will be mainly computational, but will be supported by key experimental testing. In the course of this research, the University of Edinburgh will cooperate with industrial partners in the oil & gas sector.

Further reading on this subject:
1. Michael Martinez, Aurélien Pépin, and Paul Sicsic, “Ovality Prediction of Reeled Seamless and Seam Welded Pipes.”, International Conference of Offshore and Polar Engineering, ISOPE, San Francisco, CA, June 2017.
2. Chatzopoulou, G., Karamanos, S. A., and Varelis, G. E., “Finite Element Analysis of Cyclically-Loaded Steel Pipes During Deep Water Reeling Installation.”, Ocean Engineering, Vol. 124, pp. 113–124, September 2016.