In order to effectively transport the gas in arctic or seismic region, pipeline demands linepipe steels with high deformation capacity since earth movement occurs by frost heave or earth quake. New concept of strain based design (SBD) was proposed for safe pipeline construction. In view of obtaining the material properties of X80 and X100 for SBD application, many efforts to achieve superior strain capacity have been made. The X80/X100 linepipe steel plates and pipes for strain based design were developed. The chemical composition an TMCP (Thermomechanical controlled process) parameters were designed to achieve high strength and improved toughness at body and heat affected zone, and high strain aging resistance after coating. Dual phase microstructure results in enhancing the strain aging resistance of X80/X100 linepipe steels. Several pipes of 1 meter length were made by UOE simulator and submerged arc welding was carried out for seam welding with optimum heat input, welding material and process. Mechanical properties were evaluated through plate, pipe and aged treatment specimen. In order to evaluate the compressive strain limit, buckling test was performed with long pipes of X100 before and after aging treatment. It could be realized that the developed pipes satisfy the minimum requirement of strain capacity for strain based design linepipe.
The demand of high strain capacity responding to severe earth movement has been gradually increased in recent pipeline project. The concept of strain based design (SBD) linepipe steel was proposed and many developments were actively progressed (Suzuki, 2001; Glover, 2002; Shinohara, 2005; Ishikawa, 2006; Shinohara, 2007). In order to install the pipeline at the severe region, the use of strain based design linepipe steel having high deformability is most important. Although main factors to influence the deformability of pipe are not fully understood, it is generally known that the factors are deeply related to yield ratio (yield stress/tensile stress), exponent of work hardening, and uniform elongation of linepipe steel.
