Section IV. WELDING POSITIONS
Welding is often done on structures in the position in which they are found. Techniques have been developed to allow welding in any position. Some welding processes have all-position capabilities, while others may be used in only one or two positions. All welding can be classified according to the position of the workpiece or the position of the welded joint on the plates or sections being welded. There are four basic welding positions, which are illustrated in figures 6-30 and 6-31. Pipe welding positions are shown in figure 6-32. Fillet, groove, and surface welds may be made in all of the following positions.
6-18. FLAT POSITION WELDING
In this position, the welding is performed from the upper side of the joint, and the face of the weld is approximately horizontal. Flat welding is the preferred term; however, the same position is sometimes called downhand. (See view A, figure 6-30 and view A, figure 6-31 for examples of flat position welding for fillet and groove welds).
6-19. HORIZONTAL POSITION WELDING
The axis of a weld is a line through the length of the weld, perpendicular to the cross section at its center of gravity.
a. Fillet Weld. In this position, welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface. View B, figure 6-31, illustrates a horizontal fillet weld.
b. Groove Weld. In this position, the axis of the weld lies in an approximately horizontal plane and the face of the weld lies in an approximately vertical plane. View B, figure 6-30, illustrates a horizontal groove weld.
c. Horizontal Fixed Weld. In this pipe welding position, the axis of the pipe is approximately horizontal, and the pipe is not rotated during welding. Pipe welding positions are shown in figure 6-32.
d. Horizontal Rolled Weld. In this pipe welding position, welding is performed in the flat position by rotating the pipe. Pipe welding positions are shown in figure 6-32.
6-20. VERTICAL POSITION WELDING
a. In this position, the axis of the weld is approximately vertical. Vertical welding positions are shown in view C, figures 6-30 and 6-31.
b. In vertical position pipe welding, the axis of the pipe is vertical, and the welding is performed in the horizontal position. The pipe may or may not be rotated. Pipe welding positions are figure shown in figure 6-32.
6-21. OVERHEAD POSITION WELDING
In this welding position, the welding is performed from the underside of a joint. Overhead position welds are illustrated in view D, figures 6-30 and 6-31.
6-22. POSITIONS FOR PIPE WELDING
Pipe welds are made under many different requirements and in different welding situations. The welding position is dictated by the job. In general, the position is fixed, but in sane cases can be rolled for flat-position work. Positions and procedures for welding pipe are outlined below.
a. Horizontal pipe 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. 6-33). Start welding at point C, figure 6-33, progressing upward to point B. When point 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 points B and C and the pipe rotated past it.
(2) The position of the torch at point A (fig. 6-33) is similar to that for a vertical weld. As point 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 insure 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. (0.64 cm) in thickness, a multipass weld should be made.
b. Horizontal Pipe Fixed Position Weld.
(1) After tack welding, the pipe is set up so that the tack welds are oriented approximately as shown in figure 6-34. 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 as described below.
Step 1. Starting at the bottom or 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 (fig. 6-35) and work down one side (1, fig. 6-35) to the bottom, then return to the top and work down the other side (2, fig. 6-35) 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 possible the use of greater welding speeds. 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. (0.95 cm), two passes for wall thicknesses 3/8 to 5/8 in. (0.95 to 1.59 cm), three passes for wall thicknesses 5/8 to 7/8 in. (1.59 to 2.22 cm), and four passes for wall thicknesses 7/8 to 1-1/8 in. (2.22 to 2.87 cm).
c. Vertical Pipe Fixed Position Weld. Pipe in this position, wherein the joint is horizontal, is most frequently welded by the backhand method (fig. 6-36). The weld is started at the tack and carried continuously around the pipe.
d. Multipass Arc Welding.
(1) Root beads. If a lineup clamp is used, the root bead (view A, fig. 6-37) is started at the bottom of the groove while the clamp is in position. When no backing ring is used, care should be taken to build up a slight bead on the inside of the pipe. If a backing ring is used, the root bead should be carefully fused to it. As much root bead as the bars of the lineup clamp will permit should be applied before the clamp is removed. Complete the bead after the clamp is removed.
(2) Filler beads. Care should be taken that the filler beads (view B, fig. 6-37) are fused into the root bead, in order to remove any undercut causal by the deposition of the root bead. One or more filler beads around the pipe usually will be required.
(3) Finish beads. The finish beads (view C, fig. 6-37) are applied over the filler beads to complete the joint. Usually, this is a weave bead about 5/8 in. (1.59 cm) wide and approximately 1/16 in. (0.16 cm) above the outside surface of the pipe when complete. The finished weld is shown in view D, figure 6-37.
e. Aluminum pipe welding. For aluminum pipe, special joint details have been developed and are normally associated with combination-type procedures. A backing ring is not used in most cases. The rectangular backing ring is rarely used when fluids are transmitted through the piping system. It may be used for structural applications in which pipe and tubular members are used to transmit loads rather than materials.
6-23. FOREHAND WELDING
a. Work angle is the angle that the electrode, or centerline of the welding gun, makes with the referenced plane or surface of the base metal in a plane perpendicular to the axis of a weld. Figure 6-38 shows the work angle for a fillet weld and a groove weld. For pipe welding, the work angle is the angle that the electrode, or centerline of the welding gun, makes with the referenced plane or surface of the pipe in a plane extending from the center of the pipe through the puddle. Travel angle is the angle that the electrode, or centerline of the welding gun, makes with a reference line perpendicular to the axis of the weld in the plane of the weld axis. Figure 6-39 illustrates the travel angle for fillet and groove welds. For pipe welding, the travel angle is the angle that the electrode, or centerline of the welding gun, makes with a reference line extending from the center of the pipe through the arc in the plane of the weld axis. The travel angle is further described as a drag angle or a push angle. Figure 6–39 shows both drag angles and push angles. The push angle, which points forward in the direction of travel, is also known as forehand welding.
b. In forehand welding, the welding rod precedes the torch. The torch is held at an approximately 30 degree angle from vertical, in the direction of welding as shown in figure 6-40. The flame is pointed in the direction of welding and directed between the rod and the molten puddle. This position permits uniform preheating of the plate edges immediately ahead of the molten puddle. By moving the torch and the rod in opposite semicircular paths, the heat can be carefully balanced to melt the end of the rod and the side walls of the plate into a uniformly distributed molten puddle. The rod is dipped into the leading edge of the puddle so that enough filler metal is melted to produce an even weld joint. The heat reflected backwards from the rod keeps the metal molten. The metal is distributed evenly to both edges being welded by the motion of the tip and rod.
c. This method is satisfactory for welding sheets and light plates in all positions. Some difficulties are encountered in welding heavier plates for the reasons given below:
(1) In forehand welding, the edges of the plate must be beveled to provide a wide V with a 90 degree included angle. This edge preparation is necessary to insure satisfactory melting of the plate edges, good penetration, and fusion of the weld metal to the base metal.
(2) Because of this wide V, a relatively large molten puddle is required. It is difficult to obtain a good joint when the puddle is too large.
6-24. BACKHAND WELDING
a. Backhand welding, also known as drag angle, is illustrated in figure 6-41. The drag angle points backward from the direction of travel.
b. In this method, the torch precedes the welding rod, as shown in figure 6-41. The torch is held at an angle approximately 30 degrees from the vertical, away from the direction of welding, with the flame directed at the molten puddle. The welding rod is between the flame and the molten puddle. This position requires less transverse motion than is used in forehand welding.
c. Backhand welding is used principally for welding heavy sections because it permits the use of narrower V’s at the joint. A 60 degree included angle of bevel is sufficient for a good weld. In general, there is less puddling, and less welding rod is used with this method than with the forehand method.No tags for this post.