Traditionally when the pipeline lateral buckling behaviour was analysed using Finite Element (FE) method, pipelines were normally modelled with beam elements without incorporation of torsional friction in the FE models. The neglection of torsional friction has limited impact on FE analysis results if snake lay is used as the lateral buckling initiation method, since the pipeline rotation in such a case is normally very limited. However, it could be different for a pipeline with Residual Curvature Method (RCM) used to trigger lateral buckling. If a Residual Curvature (RC) section has not been laid horizontally on seabed, its behaviour will be different from what has been expected during pipeline design, because the pipeline will have axial rotation besides lateral displacement, as a result of eccentricity caused by the suspended RC. In such a case, the effect of torsional friction between pipeline and seabed cannot be neglected.
In this paper, the torsional friction for pipelines with RC sections are discussed. The incorporation of torsional friction in pipeline FE models is presented and its effect on pipeline lateral buckling behaviour with residual curvatures is illustrated. To facilitate lateral buckling of pipelines with under-rotated RC sections, mitigation measures for are proposed and the post-laid residual curvature mitigation loading steps are included in the FE models. The effect of the torsional friction is demonstrated by introducing it in FE models with under-rotated RC sections. In the end, the validity of this method is verified by comparing the FE results with the site measurement for pipelines with under-rotated RC sections mitigated after installation on seabed. The effectiveness and the reliability of the proposed method for incorporation of torsional friction in FE analyses for pipelines with RC sections are concluded. By implementing connector elements with torsional friction properties in the FE model, a good match was observed between the predicted behaviour and the observed field measurements. This FE model can be used potentially in future projects with RC sections or with considerable pipeline rotations.
