Method for tube welding

Claim 1

A method of butt welding a pair of vertically disposed, ferrous, tubular members having a wall thickness of more than 12 mm in end-to-end relationship by multi-pass gas-shielded arc welding with a consumable electrode from the outer side of the tubular members without using a backing member, comprising the steps of (a) preparing the opposed edges of the tubular members by forming a root face on each of the opposed edges the width of which being in the range of 0.5 to 3.0 mm, beveling each of the opposed edges adjacent to the root face to a bevel angle in the range of 40° to 50°, coaxially aligning said tubular members so that the root faces of each of said tubular members are disposed in closely spaced relationship opposite and facing one another and so that said opposed beveled edges define a groove, the gap between the root faces being not larger than 1.5 mm, (b) performing a root pass by continuously feeding an electrode into the groove with its tip parallel with the root face, the diameter of said electrode being not larger than about 1.0 mm, supplying shielding gas consisting of 0-40% carbon dioxide and the balance argon, energizing an arc between the electrode and the root face, alternately changing the voltage supplied to the arc between a low value and a high value at a frequency of alternation in the range of 0.5 to 2.0 Hz, adjusting the low voltage to produce a droplet transfer of the metal from the electrode into the groove during short-circuit periods, adjusting the high voltage to produce a spray transfer of the metal, adjusting the welding speed and the electrode feeding speed to deposit metal in the groove in the range of 0.15 to 0.35 grams per mm length of the pass, and (c) Successively depositing overlapping passes by gas-shielded arc welding for filling the groove.

Claim 2

A method of butt welding a pair of vertically disposed, ferrous, tubular members having a wall thickness of more than 12 mm in end-to-end relationship by multi-pass gas-shielded arc welding with a consumable electrode from the outer side of the tubular members without using a backing member, comprising the steps of (a) preparing the opposed edges of the tubular members by forming a root face on each of the opposed edges the width of which being in the range of 0.5 to 3.0 mm, beveling each of the opposed edges adjacent to the root face to a bevel angle in the range of 40° to 50°, coaxially aligning said tubular members so that the root faces of each of said tubular members are disposed in closely spaced relationship opposite and facing one another and so that said opposed beveled edges define a groove, the gap between the root faces being not larger than 1.5 mm, (b) performing a root pass by continuously feeding an electrode into the groove with its tip parallel with the root face, the diameter of said electrode being not larger than about 1.0 mm, supplying shielding gas consisting of 0-40% carbon dioxide and the balance argon, energizing an arc between the electrode and the root face, alternately changing the voltage supplied to the arc between a low value and a high value at a frequency of alternation in the range of 0.5 to 2.0 Hz, adjusting the low voltage to produce a droplet transfer of the metal from the electrode into the groove during short-circuit periods, adjusting the high voltage to produce a spray transfer of the metal, adjusting the welding speed and the electrode feeding speed to deposit metal in the groove in the range of 0.15 to 0.35 grams per mm length of the pass, and (c) Successively depositing overlapping passes by gas-shielded arc welding for filling the groove.