The Keyhole

The keyhole is an essential part in welding a root bead. It should be about iy3 times the diameter across the electrode coating in size. The keyhole helps to insure that the deposited bead will penetrate to the root as evidenced by the small crown at the back of the bead. This crown, Fig. 4-8, should rise about inch above the inside surface of the pipe. While welding, the welder should watch the

The electrode should be held at the correct electrode angle, as shown in Fig. 4*7, A and B. It is held over the starting point until the edges of the groove begin to melt and then is shortened to obtain the correct arc length for welding. When the keyhole (Fig. 4-6B) has

The Keyhole

Fig. 4-8. The root bead. (Note the crown at the base.)

keyhole constantly. If it becomes enlarged, overpenetration will result. This can be corrected by reducing the welding current or, in some cases, by increasing the welding speed. If the keyhole is too small, the penetration of the root bead will be insufficient. While slowing the speed of welding will help in some cases, usually it is necessary to increase the welding current to correct this condition.

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