Metallurgical Design and Development of High Deformable X100 Line Pipe Steels Suitable for Strain-Based Design

The demand for natural gas using pipelines and LNG to supply the world gas markets is increasing substituting for oil and coal. The use of high strength line pipe steels provides the reduction of cost of gas transmission pipelines by enabling high-pressure transmission of large volumes of gas. In particular, high strength line pipe materials with a yield strength of X80 or higher have been developed over the last few decades around the world. Long distance gas transmission pipelines from remote areas sometimes pass through discontinuous permafrost, and are subject to ground movements by repeated thaw subsidence and frost heave. In this case, strain-based design has been applied as well as stress-based design. Therefore, high deformable line pipe is required for strain-based design in order to prevent the pipeline from fracturing. Nippon steel has also developed high deformable high strength line pipe material suitable for strain-based design. In recent years, demand for high strength line pipe steels has emerged in which the molybdenum content is reduced because of the high cost of molybdenum. Conventionally, high strength line pipe steel with Mo addition has been developed in order to control the microstructure and to obtain pipe properties such as strength and low temperature toughness. This paper describes the metallurgical design and development of high deformable high strength X100 line pipe with lower Mo content suitable for strain-based design. High deformable X100 line pipe with 16 mm wall thickness as well as good low temperature toughness and seam weld toughness has been developed.