The 5G horizontal fixed position is the most commonly used pipe welding position,and also is considered to be one of the most difficult welding positions to work with (Ref. 30). The pipe is fixed parallel to the horizon and the weld is made vertically around the pipe. When welding
around the pipe joint circumference, several common welding positions or their combinations are encountered, including 1G flat, 3G vertical, and 4G overhead.The dynamic development of the weld
pool was analyzed without exclusively including the gravitational force that changes with the welding position but simply assuming that a nonzero width of the bottom weld pool surface would result in a sufficient positive e_bv to balance out and exceed the increase in Δv. At the top
position (1G flat), both the arc force and gravitational force tend to produce a sufficiently
positive ebv. At the side position (3G vertical), the arc force tends to produce a sufficiently positive ebv. The dynamic development of the weld pool behaves as illustrated in Fig. 3.
However, at the bottom position (4G overhead), the gravitational force acts against the arc force that pushes the liquid metal toward the bottom weld pool surface to produce a positive ebv>0. If the arc force is insufficient to significantly exceed the gravitational force, the vertex may not occur even if an adequate width of the bottom weld pool surface has been produced.Some typical problems at the bottom position due to an insufficient arc force are
illustrated in Fig. 7.In Fig. 6, the peak current was 110 A.In Fig. 7A, the arc pressure was not sufficient to overcome the gravitational force and surface tension to effectively produce
a sufficient positive ebv to balance out and exceed the increase in Δv such that d(Δv)/dt