To ensure the strain capacity of the pipeline, low-stress brittle fractures should first be avoided. The types of failure in welding joints of pipelines can be divided into fracture and plastic collapses. It is important to predict and evaluate the strain capacity of the welding joint. Thus, the strain capacity of the pipeline is dependent on the welding joint. Usually, the deformation capacity of a welding joint is less than that of the pipe metal, and girth welds are weak points in the pipeline. The strain capacity of a pipeline is required to meet the needs of the service environment, which is the principle on which the strain-based pipeline design method is based. A compressive strain is formed in the side of the bending pipeline and a tensile strain is formed at the back. Moreover, bending of the pipeline will occur as waves move, and the axial load of the pipeline is generated by bending. The axial load of the pipeline is added during the reel-laying process, and a compressive or tensile strain is developed. In the marine pipeline construction stage, reel barges are used for pipe-laying. High-strain capacity pipe is needed for operation in the marine environment, both at the construction stage and in service. Due to the high-pressure design of marine pipeline, new requirements for the grade, diameter and thickness of pipes should be explored. With the discovery of abundant offshore oil and gas resources in deep-sea areas and the rapid growth in the marine pipeline industry, new developments that enable high operating pressure, long-distance traverses, and large diameter piping are essential.
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