Determination of Preconditions Leading to Critical Stresses in Pipeline During Lowering

Abstract

The problem of changing the spatial position of pipelines at different stages of their life cycle is described. The stages and conditions of pipeline construction or operation as well as different modes of technological equipment operation mainly effect on it. In various applied researches of these processes, an attention is mainly paid to recommendations on how to achieve the optimal mode of bending the pipeline. However, in the practice of pipelines construction and operation, the optimal load mode of equipment rarely becomes the subject of interest. In the first place becomes the issue of ensuring the load regime within the permissible limits. To define them a finite-element model of a hypothetical pipeline was created. After defining loads and impacts occurring within the typical pipeline construction sequences as well as under pipelines operation appropriate pipeline deformations were obtained. The processes of pipeline constructing both onshore and offshore (so called S-method) was taken into account. It is shown that the range of permissible pipeline displacements during pipeline lowering on the seabed is an order of magnitude lower than the one on land. It was found that bending stresses in the pipeline are mainly determined by the angle of inclination of the stinger and the axial tension force of the pipeline laying ship. Concerning onshore pipeline construction process they are determined by the position of the first pipelaying crane (so called side boom) from the laying side. Dependence of critical values of process managing parameters from the pipe laying conditions was obtained.