Property of X80 Grade SAW Pipes for Resistance to Ground Movement

It is aware that the expansion of gas utilization is an important issue to restrict CO₂ emission. The reduction of gas transportation cost is essential to increase gas supply to market. The high-pressure gas pipeline with high strength pipes has contributed for safe and economical transportation of natural gas and is expected more for the future demand of gas. The primary objective of high strength line pipe is to hold high pressure safely. The property in circumferential direction under hoop stress is the primary target of the line pipe. High strength and high toughness steel at low temperature has been developed for large diameter line pipes, which have been supplied to major gas pipelines. The increase of D/T of pipelines for transportation efficiency tends to decrease critical compressive strain. Since long distance pipelines come across various ground conditions, the pipeline might encounter some serious ground movement. It is pointed out that in this event the strain by the ground movement might be high enough to deform pipelines to leak or rupture. There are various forms of ground movement, but the Japanese guideline for earthquake resistance and liquefaction is considered as basic conditions for SBD and for FEA in this study. The relation between pipe deformation and property in axial direction is investigated to identify the effective parameter to design the steel property for gas pipelines. Metallurgical factors and microstructure can change the parameters not only on strength and toughness, but also on the critical strain of X80 line pipes. It is discussed that the effectiveness of those changes to improve the safe operation of high-pressure gas pipelines with X80 grade line pipe.