Efficient methods to mitigate SCR-induced walking of short subsea flowlines

Abstract

Steel catenary riser is a long-established option for subsea projects in deep-water regions. Sustained pulling force of steel catenary risers on subsea flowlines in combination with cyclic thermal load throughout the system lifetime may lead to progressive global axial displacement of subsea pipelines which has been termed as ‘walking’. One of the challenges in the deep-water industry is long-term walking of subsea flowlines in a cumulative manner. Common practice methods for walking mitigation are quite expensive operations. State-of-the-art mitigation strategies are proposed in the paper by means of modifying pipe pieces before the installation operation. Bowed pipe pieces and miter joints are two recommended approaches for walking mitigation. The presented mitigation strategies are relatively cost-effective solutions for the pipe-walking challenge and they are able to considerably cease the potential cyclic walking. Comprehensive FE analyses in ABAQUS software are performed to evaluate the proposed deformed pipelines response subject to two loading conditions. Through-life integrity of the suggested pre-deformed pipeline is assessed in terms of effective axial force, local buckles and excessive axial strains. A comparison of the presented method with conventional techniques shows the effectiveness of the proposed configuration. The proposed methods can significantly reduce effective axial force throughout the subsea pipeline by means of artificially introduced deformations. The cumulative walking of the presented method is practically zero. In addition, the influence of combined triggering mechanisms to the walking phenomenon is assessed when the pipeline is located on a sloping seabed and it is subject to non-uniform thermal loads. A parametric study is performed to improve confidence in design and provide a reasonably practical technique with an optimal shape.