Metallurgical Design and Development of High-Grade Line Pipe

The application of high-strength line pipes has enabled pipelines to operate at high pressure, generating cost savings for both gas transportation and construction. In general, high-strength line pipes require crack initiation resistance and crack arrestability at low temperatures, as well as field weldability. High strength and deformability for strain-based design and excellent sour resistance are also required. Moreover, composite properties are often required for high-strength line pipes. This paper describes our progress in this field with regard to metallurgical design and development. Metallurgical design aimed at achieving a good balance between strength, low temperature toughness and deformability for strain-based design is also described from the perspectives of grain refinement, microstructure and chemical composition. Metallurgical design focused on a good balance between strength and sour resistance in limited low chemical composition is described from the perspectives of microstructure and control to chemical composition and center segregation. These efforts have led to the development of high-strength heavy wall line pipes of API X60 to X100 grades offering excellent low temperature toughness and high deformability for stain-based design, while API grades X65 to X70 with good sour resistance have also been developed.