气体保护金属极电弧焊SMAW is shielded [I]meta[/I]l arc welding XX;6 P 气体金属电弧焊Gas [I]meta[/I]l Arc Welding (GMAW) process u=K2Q4 气体钨极电弧焊GTAW is gas tungsten arc welding 气体保护焊机Gas protective welder MiGcA EF;桥梁bridge girder <e"J4gZf& 桥面纵坡longitudinal slope of the bridge surface 切入点feeding-in point ;) 屈服强度yield strength