Effects of boundary conditions on testing of pipes and finite elements modelling

The design of many submarine pipelines, especially for operating in deep water, relies on accurate test results for the local buckling collapse of pipe subjected to bending loading. Recent test results have shown apparently anomalous values of axial tensile and compressive strains in comparison to the values that would be expected on the basis of the simple bending theory. This could have important consequences for the efficacy of the design factors derived using these anomalous results. Examples of anomalous test results are given in the paper and the cause of the differences between the strain values obtained in the tests and those expected on the basis of the simple bending theory are explained using finite element modelling. The major point is that the general application of the simplified engineering theory of bending can be erroneous when ovalisation is imposed or, on the contrary, the boundary conditions of the section are restrained from ovalising deformations. This is a crucial limit state for the design of onshore and offshore pipelines.