Material Development of X80 for Strain-Based Design Applications

Abstract

Due to the further increasing demand for natural gas, the construction of long-distance pipelines traversing through seismically active regions or arctic regions with ground movement caused by permafrost phenomena will become more and more necessary. To guarantee the safe operation of those pipelines, the pipe material has to fulfill strain-based design requirements in the coated condition. Hence in longitudinal direction low yield-to-tensile ratios, high uniform elongation values and a roundhouse shape of the stress-strain curve combined with sufficient strength values in transverse direction are essential. The basis for appropriate pipe properties is an adequate design of the plate material. To achieve these objectives the microstructure has become a central element. Nevertheless, it has to be taken into account that the cold deformation during the pipe manufacturing process and the heat treatment of the pipe during the subsequent coating have a major influence on the final line pipe behavior. The current paper describes recent development steps and approaches. The mechanical properties of the different concepts will be compared and the advantages and disadvantages will be highlighted.