The procedures given in this chapter are recommended for weld­ing the root bead on all heavy-wall pipe. In the following discussion 8-inch Schedule 60 mild steei pipe will be used as the example of welding in the 5G position. The actual outside diameter is 8.625 inches and the wall thickness is.406 inch. For welding this pipe a y8-inch E6010 electrode should be used. The pipe should be clamped on the fixture with the tack welds in the 2, 5, 8, and 11 o’clock positions, as shown in Fig. 5-2C. Since the pipes to be welded are heavy-wall pipes, the uphill welding method will be used. The general procedure is to start at the 6:30 o’clock position and to weld up to the 12 o’clock position around one side of the pipe, and again, from the 6:30 o’clock to the 12 o’clock positions around the other side of the pipe, to close the weld.

Three basic welding positions are used to weld the root bead when the pipe is in the horizontal, or 5G, position. The weid is started by welding in the overhead (4G) position; then gradually there is a

change to the vertical (3G) position, welding in the uphill direction. From this position there is another gradual transition to the flat (1G) position.

When welding around the pipe from the bottom to the top, the transitions from one position to another are gradual. This requires the welder to be alert in order to maintain the correct electrode angle at all times and to change his welding technique as necessary.

Welding in each of the positions will be described separately. How­ever, the welder must develop the skill to recognize whjch welding method to use and when a change must be made.

The Keyhole

Before going further, it is necessary to say a word about the keyhole. As seen in Fig. 5-4, the keyhole is a teardrop or pear-

shaped enlargement of the root opening ahead of the bead. When welding a root bead, the keyhole is necessary in order to obtain the required weld penetration.

The keyhole is the basic guide to the welder as he welds the root bead. When starting to weld, the welder should make certain that the keyhole has formed. The correct amount of penetration is obtained when the keyhole is about lk times the diameter across the elec­trode coating, or slightly less. While welding the root bead, the welder must pay careful attention to the keyhole and watch for changes in its size. If it becomes enlarged, excessive penetration, burn-through, or internal undercut will result. If it is too small, the penetration of the root bead will be insufficient to produce a satisfac­tory weld. These defects are shown later in Fig. 5-14.