Experimental and numerical studies on collapse of subsea pipelines with interacting corrosion defects

Abstract

The pipeline is prone to collapse under the combined external pressure and multiple corrosion defects. Experiments of the full-scale pipelines with longitudinally, circumferentially and diagonally dual defects are conducted, respectively. Finite element models are established to simulate the experimental process, and achieved good consistency. Then the influences of corrosion defect dimensions on the interaction are analyzed, and the corresponding critical spacing is determined. Moreover, the collapse modes of the pipeline under different defect forms are studied. The collapse mode of the pipeline with two external corrosion defects changes from U-shaped to ∞-shaped mode. However, the collapse modes for the pipeline with internal and external corrosion defects or two internal corrosion defects are irregular and the deformation is mainly concentrated on the region of corrosion defects. In addition, the critical pressure of the pipeline is sensitive to the defect distribution type (distributed axially, circumferentially, or diagonally along the pipeline, etc.). Finally, a formula for estimating the collapse pressure of the pipeline with dual corrosion defects is proposed. The comparison between the proposed formula and finite element results proves that this formula can be used for the collapse pressure of the pipeline with multiple corrosion defects in a slightly conservative manner.