Figure 3-23.Butt joints.
Whether the load will be in tension or compres-
sion and whether bending, fatigue, or impact
stresses will be applied
How a load will be applied; that is, whether the
load will be steady, sudden, or variable
The direction of the load as applied to the joint
The cost of preparing the joint
Another consideration that must be made is the ratio
of the strength of the joint compared to the strength of
the base metal. This ratio is called joint efficiency. An
efficient joint is one that is just as strong as the base
Normally, the joint design is determined by a de-
signer or engineer and is included in the project plans
and specifications. Even so, understanding the joint
design for a weld enables you to produce better welds.
Earlier in this chapter, we discussed the five basic
types of welded jointsbutt, corner, tee, lap, and edge.
While there are many variations, every joint you weld
will be one of these basic types. Now, we will consider
some of the variations of the welded joint designs and
the efficiency of the joints.
The square butt joint is used primarily for metals
that are 3/16 inch or less in thickness. The joint is
reasonably strong, but its use is not recommended when
the metals are subject to fatigue or impact loads. Prepa-
ration of the joint is simple, since it only requires match-
ing the edges of the plates together; however, as with
any other joint, it is important that it is fitted together
correctly for the entire length of the joint. It is also
important that you allow enough root opening for the
joint. Figure 3-23 shows an example of this type of joint.
When you are welding metals greater than 3/16 inch
in thickness, it is often necessary to use a grooved butt
joint. The purpose of grooving is to give the joint the
required strength. When you are using a grooved joint,
it is important that the groove angle is sufficient to allow
the electrode into the joint; otherwise, the weld will lack
penetration and may crack. However, you also should
avoid excess beveling because this wastes both weld
metal and time. Depending on the thickness of the base
metal, the joint is either single-grooved (grooved on one
side only) or double-grooved (grooved on both sides).
As a welder, you primarily use the single-V and double-
V grooved joints.
The single-V butt joint (fig. 3-23, view B) is for
use on plates 1/4 inch through 3/4 inch in thickness.
Each member should be beveled so the included angle
for the joint is approximately 60 degrees for plate and
75 degrees for pipe. Preparation of the joint requires a
special beveling machine (or cutting torch), which
makes it more costly than a square butt joint. It also
requires more filler material than the square joint; how-
ever, the joint is stronger than the square butt joint. But,
as with the square joint, it is not recommended when
subjected to bending at the root of the weld.
The double-V butt joint (fig. 3-23, view C) is an
excellent joint for all load conditions. Its primary use is
on metals thicker than 3/4 inch but can be used on
thinner plate where strength is critical. Compared to the
single-V joint, preparation time is greater, but you use
less filler metal because of the narrower included angle.
Because of the heat produced by welding, you should
alternate weld deposits, welding first on one side and
then on the other side. This practice produces a more
symmetrical weld and minimizes warpage.
Remember, to produce good quality welds using the
groove joint, you should ensure the fit-up is consistent
for the entire length of the joint, use the correct groove