Pipelines may be loaded by many different loads, such as internal and/or external pressure P, loads caused by differences in the settlements along the pipeline, temperature, etc. Where the pipeline changes horizontal direction, e.g. due to a horizontal bend in a buried pipeline, the aforementioned loadings will cause bending moments and torsional moments in the bend and in the connected straight pipe. Such situations may occur onshore but also offshore near platforms. The relation between the pressure P, the bending moment Mb and torsional moment Mt after yielding, depends on the relation between imposed bending curvature C and torsional deformation Θ. With the Von Mises yield surface and the normality principle, relatively simple analytical models are derived to determine the relations between Mb, Mt, P, C, Θ and the ovalization. The model for the relation between Mb, Mt, P, C and Θ, and criteria for local buckling caused by combinations of the aforementioned forces and deformations are presented in the paper. Also test results and the results of finite element calculations are presented and compared with the analytical models. The paper is restricted to the behaviour of initially straight pipes (no bends). For bends, reference is made to Gresnigt, 1986, 1993.
Pipelines may be loaded by many different loads, such as internal and/or external pressure, surrounding soil, bending moments, normal force, shearing force and sometimes also torsion. In onshore pipelines, torsion may occur in settlement areas when a pipeline changes horizontal direction. Examples are several crossings of pipelines with dykes in The Netherlands, see Fig. I. In order to obtain extra flexibility to allow for settlements of the dyke, in some cases so called "recumbent arch" constructions were applied. The extra flexibility comes from the longer pipe length and especially the longer bends with their lower bending stiffness and greater deformation capacity compared to straight pipes.
