Uphill Welding the Root Bead
With the keyhole and the puddle established and with the electrode held at the correct angle, the electrode is advanced around the bottom of the pipe. There is no back-and-forth motion across the pipe joint, only a linear, or straight, movement along the joint in the direction of welding. The movement of the electrode should be slow and uniform. Maintaining the correct arc length, the end of the
Fig. 5-7. Welder’s view when welding the root bead at the bottom of the pipe.
electrode should be kept near the top of the keyhole, which is the part of the keyhole adjacent to the deposited weld bead. The position of the electrode is shown in Fig. 5-7. If the current setting is correct, it should not be necessary to resort to whipping in order to control the puddle and the size of the keyhole.
While welding, the welder should pay careful attention to the puddle and to the keyhole. As the electrode moves along at a steady pace it melts the edges of the bevel in front of the arc and the molten metai flows toward the back of the arc. There it enters the puddle and flows into the root opening. As the electrode moves on, the molten metal in the puddle that is left behind solidifies to form the weld bead. Since the bead will be deposited in a circular pattern around the pipe, the tilt of the electrode must be changed gradually to maintain the correct electrode angle.
If the keyhole size becomes too small, the electrode angle should be decreased slightly by pointing the electrode more directly toward the keyhole. Also, the welding speed may be decreased slightly. Should the keyhole become enlarged, the remedy is to increase the electrode angle slightly. If this is not effective, welding should be stopped and the current setting reduced before proceeding again.
Whipping is sometimes used in overhead welding to reduce the keyhole size and to control the puddle. However, this practice is not recommended and should not be used unnecessarily in the overhead position. When excessive whipping appears to be necessary, it is best to reduce the current setting.
Stop and Restart. When welding the root bead, the electrode is consumed and will need replacement. This necessarily involves breaking the arc. Welding is also stopped after a tie-in has been made with another weld, such as a tack weld; however, the procedure for making a tie-in will be treated later on in this chapter.
To stop the weld, the arc is broken by making a quick stab through the keyhole with the electrode and then by withdrawing it quickly to clear the work. By this procedure a full size keyhole is left so that complete penetration can be obtained when the weld is started again.
Before restarting the weld, the slag coating of the weld bead should be chipped off with a chipping hammer and the bead should be wire brushed for a distance of 1 inch, or more, from the keyhole. All traces of the slag coating should be removed to eliminate the danger of any of it being trapped in the molten metal when restarting.
To restart the weld, the arc should be struck on the part of the bead that has been cleaned. Maintaining a slightly longer than
normal arc, the electrode should be brought forward to the edge of the keyhole and held there momentarily to allow the arc to stabilize and the gaseous shield to form, it is also held at this length in this position to allow time for the liquid puddle to form at the edge of the keyhole. When sufficient liquid metal appears at the edges of the keyhole, but not before, the arc can be shortened to its normal length and the electrode manipulation can be started to resume the weld.
Vertical Uphill Welding of the Root Bead
The nature of the welding process changes gradually from overhead welding to vertical uphill welding as the bead progresses from the 5 o’clock to the 4 o’clock position. As the weld moves toward the vertical position, it becomes apparent that the liquid metal will tend to flow downward at a faster rate than when welding in the overhead position.
When the continuous application of heat resulting from the slow steady movement of the electrode starts to cause an overflow of the molten metal, the remedy is to resort to the whipping procedure. The whipping procedure must always be used when welding in the vertical uphill portion of the pipe. It is continued until the weld is stopped at the 12 o'clock position.
Fig. 5-8. Correct electrode angle for vertical uphill welding of the root bead of a
The electrode must be held at the correct angle, as shown in Fig. 5-8, and the electrode must follow the path shown in Fig. 5-9A. It is moved upward about one electrode diameter, Fig. 5-9B, and then returned to the face of the keyhole, which should be about one and one-half the electrode diameter.
The electrode should then pause at the face of the keyhole, which is the lower part of the keyhole adjacent to the deposited weld bead. In this area the intense heat of the arc can be absorbed by the metal, and the filler metal from the electrode is deposited here in order to build up the bead progressively. The electrode should not pause
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Fig. 5-9. A. Welder’s view uhen whipping, showing the path of the electrode. B. The length of the stroke when whipping should be approximately one electrode diameter but should not exceed 1 V% electrode diameters.
directly over the keyhole because the initial heat in this area will cause the intense heat of the arc to melt the edges around the keyhole. This will result in excessive penetration and possible burn - through.
Whipping should be done by a precise wrist movement and not by moving the entire forearm. This procedure can be described as a repeated “whip and pause.”
The objective of whipping is to allow the molten pool of metal to cool sufficiently to lose some of its fluidity. When the molten metal in the puddle is somewhat mushy, a further deposit of filler metal from the electrode will not cause it to overflow.
The length of the stroke when whipping should not be excessive. If it is excessive, the hot liquid metal in the puddle will be exposed to the atmosphere as a result of the removal of the gaseous shield. Rapid oxidation will result, which leads to porosity in the weld. Excessive whipping can also cause slag entrapment in the weld.
Some welders have a tendency to use a current setting that is too high. Then, to prevent overflowing, they resort to whipping, even in the overhead position which soon becomes excessive. In such cases, better results are obtained if the welding current is reduced and whipping is kept to a minimum. The length of stroke when whipping should not exceed one and one-half electrode diameters and preferably be less, in order to minimize the effect of uncovering the gaseous shield from the weld and to prevent slag entrapment.
Conditions approaching flat welding occur as the weld progresses to the vicinity of the 1 o’clock position. When this occurs, the molten pool of metal becomes even more difficult to control and the whipping procedure must be continued until the weld is stopped in the 12 o’clock position.
When welding a single-vee groove, open butt joint in the flat (1G) position, the molten metal will tend to drip through the opening causing the bottom of the weld to build up and form a high crown. This is excessive penetration. In more severe cases, burn-through will result, especially if the current setting is too high. In some shops, back-up plates are positioned at the bottom of the joint to prevent this from happening. However, this is not necessary when the weld is made by a skilled welder, using the whipping procedure and the correct current setting.
Fig. 5-10. Correct electrode angle for flat welding at the top of the pipe.
normal electrode angle for welding in this position is shown in Fig. 5-10A. If this does not help, the weld should be stopped and the current setting reduced. Excessive whipping should not be used to correct this situation.
From what has been said above, it is evident that the welder must watch the puddle and the keyhole for signs of excessive penetration. He must continue the whipping procedure to control the pool of molten metal. If signs of excessive penetration occur, he may increase the electrode angle somewhat as shown in Fig. 5-1 OB. The
If the current setting is correct and the correct whipping procedure is used, a perfect root bead can be welded in the flat position on top of the pipe joint. When the we]d bead has reached the 12 o’clock position, the weld should be stopped by stabbing the electrode quickly through the keyhole and withdrawing it when the arc is quenched. After the weld has cooled sufficiently, the slag coating is removed in preparation for welding the second half of the pipe joint,
Welding the Second Half of the Pipe Joint. The procedures used for welding the second half of the pipe joint are identical to those used in welding the first half.
To start the second half of the pipe joint, a restart must be made in the 6:30 position against the starting point of the first root bead. It is advisable to restart with a new electrode so that a continuous bead can be deposited, if possible, until a tie-in is made to the tack weld in the vicinity of the 8 o’clock position. Then, after making a restart at the other end of the tack, the weld is made around the pipe, stopping when necessary to replace the electrode and to make the tie-in with the remaining tack weld, until the final tie-in is made at the 12 o’clock position to close the weld. The procedure for making a good tie-in, which must be mastered, is given in the next section.