Figure 3-33.Intermittent welds.
Figure 3-34.Back-step welding.
Proper Edge Preparation and Fit-up
As discussed earlier in this chapter, proper edge
preparation and fit-up are essential to good quality
welds. By making certain the edges are properly beveled
and spacing is adequate, you can restrict the effects of
distortion. Additionally, you should use tack welds,
especially on long joints. Tack welds should be spaced
at least 12 inches apart and run approximately twice as
long as the thickness of the weld.
Control the Heat Input
You should understand that the faster a weld is
made, the less heat is absorbed by the base metal. As you
gain welding experience, it will become easier for you
to weld a seam with the minimum amount of heat by
simply speeding up the welding process.
Regardless of your experience, it is often necessary
to use a welding technique designed to control heat
input. An intermittent weld (sometimes called a skip
weld) is often used instead of one continuous weld.
When you are using an intermittent weld, a short weld
is made at the beginning of the joint. Next, you skip to
the center of the seam and weld a few inches. Then, you
weld at the other end of the joint. Finally, you return to
the end of the first weld and repeat the cycle until the
weld is finished. Figure 3-33 shows the intermittent
Another technique to control the heat input is the
back-step method (fig. 3-34). When using this tech-
nique, you deposit short weld beads from right to left
along the seam.
Preheat the Metal
As discussed earlier, expansion and contraction
rates are not uniform in a structure during welding due
to the differences in temperature throughout the metal.