Abstract: Girth welding of φ1422 mm×32.1 mm X80 steel pipe was carried out by GMAW automatic welding and GTAW+FCAW-G combined automatic welding, respectively.The strength and toughness of the girth welded joints were tested by conventional tensile test and instrumented impact test, and the strain capacity and structural reliability of the girth welded joints with defects were tested by wide plate tensile test.The results show that the X80 girth welded joints with GMAW automatic welding and ER80S-G solid welding wire are high strength matching.And the girth welded joints with GTAW+FCAW-G combination automatic welding and ER55-Ni1 and E91T1-K2MJ wires are equal strength matching.The girth welded joints of the two processes has good low temperature toughness, and the ductile-brittle transition temperature of the weld and heat affected zone is below -65 ℃and-45 ℃, respectively.Even with welding defects of size 50 mm×3 mm, the average tensile strain capacity of girth welded joints by GMAW automatic welding and GTAW+FCAW-G combined automatic welding is 6.0%, 3.5%, respectively.It shows that the two girth welded joints are safe and reliable under tensile loads.