The Characteristics of Girth Welds for Strain-Based Design API-X100 Grade Plate and Pipe

As the major oil wells run dry, many efforts on exploring a new one are under way especially in the northern area of the Earth. In this cold environment, the pipelines should have a distinctive ability of being able to endure the large longitudinal strain caused by the ground movements, such as seismic activity, slope instability, frost heave and so on. To overcome these difficulties strain-based design (SBD) of pipeline is getting spotlighted, and POSCO has developed SBD API-X80 including higher grades of line pipe steels. In this work noticing that the reliability of girth welds becomes more important in SBD compared with stress-based design, ways to improve the reliability of girth welds in a SBD API-X80 grade steel have been investigated. Mechanical and metallurgical properties were evaluated, and further CTOD tests in mechanized gas metal arc (GMA) girth welding with narrow gap grooves were conducted and the results were discussed.