A TIG welding filler metal is provided that has a composition including, by mass %, C: 0.20 to 0.80%, Si: 0.15 to 0.90%, Mn: 15.0 to 30.0%, P: 0.030% or less, S: 0.030% or less, Cr: 6.0 to 15.0%, and N: 0.120% or less, the balance being Fe and incidental impurities. Where necessary, the filler metal may contain one or two selected from Ni and Mo, may further contain one, or two or more selected from V, Ti, and Nb, and may additionally contain one, or two or more selected from Cu, Al, Ca, and REM. This configuration reduces the occurrence of welding cracks during TIG welding, that is, realizes excellent hot crack resistance, and allows for easy production of a weld joint having high strength and excellent cryogenic impact toughness.

An orbital welding system is disclosed for joining a riser to a pulled collar on a manifold runner with a circumferential weld bead, which includes a multi-axis welding platform, a weld head assembly supported on the welding platform and including a shaft housing, an electrode drive shaft mounted for axial rotation within the shaft housing, a drive motor connected to the electrode drive shaft for axially rotating the electrode drive shaft, and a torch assembly that rotates with the electrode drive shaft and includes a vertical torch shaft having an electrode holder at an upper end thereof for retaining a tungsten electrode.