Horizontal Pipe Welding (2G)
When the pipes are in a vertical position, the welding procedure used is essentially that which is used for horizontal welding and for this reason this chapter is entitled, “Horizontal Pipe Welding.” Horizontal pipe welding presents a few difficulties that are characteristic of welding in the 2G position. The molten metal in the puddle constantly tends to drip downward. The edge of the upper pipe, when in a fluid state, also flows downward causing undercuts and the development of a very large keyhole when welding the root bead. Therefore, certain correct welding practices, as described in this chapter, must be used to overcome this difficulty.
Fig. 9-І. Perfect pipe weld made in the horizontal (2G) position,
An illustration of a good horizontal weld made on a thick-wall pipe is shown in Fig. 9-І. The width of each bead or layer of weld metal should not exceed approximately three times the diameter of the electrode in order to avoid excessive weaving. For this reason more layers of weld metal are required when welding pipes in the horizontal position. After the root bead and the second pass are welded, the following beads are deposited in the manner of a bricklayer laying bricks in constructing a wail. A foundation layer is first welded in place and following layers are welded on top of it. Instead of having a single bead, the cover layer is built up in this fashion, using several beads.
In order to make high-quality welds, the welder must learn the correct technique and then apply it with consistency. The weave motion must be unchanging as the welder welds around the pipe. The same arc length, speed of welding, and electrode angle must be maintained. While welding the root bead the keyhole must be watched and during welding of all beads the welder must watch the pool of molten metal.
Preparation for Welding. Most of the procedures used to prepare the pipes for welding have been described in detail in Chapter 4 and need not be repeated here. The reader should review these procedures before going on.
For practice welding, it is best to use two 7-inch-long pipe nipples. The bevel must be cut to standard specifications and thoroughly cleaned. The pipes are then placed on end on the welding table with a bent wire spacer between them to obtain the correct root opening. After they are aligned, four evenly spaced tack welds are welded in the root of the welds as before.