Pipe Welding Procedures
Horizontal Pipe Welding Rolled Weld
(1) Align the joint and tack weld or hold in position with steel bridge clamps with the pipe mounted on suitable rollers (fig. 12-42). Start welding at point C, figure 12-42, progressing upward to point B. When B is reached, rotate the pipe clockwise until the stopping point of the weld is at point C and again weld upward to point B. When the pipe is being rotated, the torch should be held between B and C and the pipe rotated past it.
(2) The position of the torch at A (fig. 12-42) is similar to that for a vertical weld. As B is approached, the weld assumes a nearly flat position and the angles of application of the torch and rod are altered slightly to compensate for this change.
(3) The weld should be stopped just before the root of the starting point, so that a small opening remains. The starting point is then reheated, so that the area surrounding the junction point is at a uniform temperature. This will ensure a complete fusion of the advancing weld with the starting point.
(4) If the side wall of the pipe is more than 1/4 in. (6.4 mm) in thickness, a multipass weld should be made.
Horizontal Pipe Welding Fixed Position Weld
(1) After tack welding, the pipe is set up so that the tack welds are oriented approximately as shown in figure 12-43. After welding has been started, the pipe must not be moved in any direction.
(2) When welding in the horizontal fixed position, the pipe is welded in four steps.
Step 1. Starting at the bottom of 6 o’clock position, weld upward to the 3 o’clock position.
Step 2. Starting back at the bottom, weld upward to the 9 o’clock position.
Step 3. Starting back at the 3 o’clock position, weld to the top.
Step 4. Starting back at the 9 o’clock position, weld upward to the top overlapping the bead.
(3) When welding downward, the weld is made in two stages. Start at the top overlapping the bead. (fig. 12-44) and work down one side (1, fig. 12-44) to the bottom, then return to the top and work down the other side (2, fig. 12-44) to join with the previous weld at the bottom. The welding downward method is particularly effective with arc welding, since the higher temperature of the electric arc makes the use of greater welding speeds possible. With arc welding, the speed is approximately three times that of the upward welding method.
(4) Welding by the backhand method is used for joints in low carbon or low alloy steel piping that can be rolled or are in horizontal position. One pass is used for wall thicknesses not exceeding 3/8 in. (9.5 mm), two passes for wall thicknesses 3/8 to 5/8 in. (9.5 to 15.9 mm), three passes for wall thicknesses 5/8 to 7/8 in. (15.9 to 22.2 mm), and four for wall thicknesses 7/8 to 1-1/8 in. (22.2 to 28.6 mm).
Vertical Pipe Welding Fixed Position Weld
Pipe in this position, where the joint is horizontal, is most frequently welded by the backhand method (fig. 12-45). The weld is started at the tack and carried continuously around the pipe.
Multipass Arc Pipe Welding
(1) Root beads. If a lineup clamp is used, the root bead (A, fig. 12-46) is started at the bottom of the groove while the clamp is in position. When no backing ring is used, take care to build up a slight bead on the inside of the pipe. If a backing ring is used, the root bead must be carefully fused to it. As much root bead as the bars of the lineup clamp permit should be applied before the will clamp is removed. Complete the bead after the clamp is removed.
Posted in: Pipe Welding
April 28, 2011