Machinery's Handbook, 31st Edition
Pipe Welding
1615
9) Current and voltage must be related to the pipe wall thickness. 10) Argon + 25 percent CO 2 is recommended for short circuit welding of pipe roots. 11) Use of undiluted CO 2 gas will improve MIG weld fusion in fill passes because of the “digging” action of the arc, and the increased weld energy. 12) With pipe wall thicknesses of 0.4 inch (10 mm) or greater, preheating to between 400 and 500°F (205 and 260°C) will help make fusion complete. Other Methods.— Pulsed MIG is a viable alternative to flux-cored for all-position welds on 5G pipe, but requires more costly equipment. The pulsed MIG process however, has few advantages over conventional MIG and flux-cored when the latter are used correctly. Pulsed MIG may have some advantage on mechanized 5G welds and on welding of stain less steel pipe in the 5G position. Metal-cored electrode wire also has few advantages for pipe welds because they work best with low-energy gas welds, which cancels out the increased current density claimed for them. On most manual pipe welds, the welder needs time to control and direct the weave to ensure even heating and avoid lack of fusion. Satisfactory welds are often performed at travel speeds of 4 to 12 in/min (0.10–0.31 m/min) giving deposit rates of 3–5 lb/hr (1.36– 2.27 kg/hr). Pipe Welding Procedure Because of the variety of parameter combinations that can be used in pipe welding, it is suggested that charts be prepared and displayed in welding booths to remind welders of the basic settings to be used. Examples of such charts for tack, root, fill and cover passes, are included in what follows: FCAW 5G (Non-Rotated) MIG Welding of Thick-Walled, Carbon Steel Pipes, Proce dure for Root Welding.— This procedure can be applied to most pipe sizes, and should be given special consideration for 5G (non-rotated) welds on carbon steel pipe with 3 ∕ 8 inch (10 mm) wall thickness and thicker. Pipe and Weld Data Pipe bevel included angle = 80 Root face land = 3 ∕ 32 ± 1 ∕ 32 inch (2.4 ± 0.8 mm) Root gap between faces = 5 ∕ 32 ± 1 ∕ 32 inch (4 ± 0.8 mm) Electrode for root weld = 0.035-inch (0.9 mm) diameter, E70S-3 flux-cored Gas = argon with 15–25% CO 2 Gas flow rates = 30 to 40 cubic ft/hr (0.85–1.13 m 3 /hr) Set wire feeder to 210–280 in/min (10 to 11 o’clock position on many feeders) for current of 140–170 amps, 17–18 volts. Wire extension: For MIG root weld, set contact tip to stick outside the nozzle, 1 ∕ 16 to 1 ∕ 8 inch (1.6 to 3 mm). Maintain 3 ∕ 8 to 5 ∕ 8 inch (10 to 16 mm) maximum wire stick out from contact tip. Tack Welding Procedures for FCAW 5G Pipe Welds: Make tack welds 1.5 to 2 inches (38 to 50 mm) long. After welding, grind full length of tack to thickness of approximately 1 ∕ 16 inch (1.6 mm). Feather tack ends back 3 ∕ 8 to 1 ∕ 2 inches (9.5 to 13 mm). On pipes of less than 6 inches (15 cm) outside diameter, use three tack welds, equally spaced, starting at 12 o’clock.
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