The details of a joint, which
includes both the ge-ometry and the required dimensions, are called the joint design. Just
what type of joint design is best suited for a particular job depends on many factors.
Although welded joints are designed primarily to meet strength and safety requirements,
there are other factors that must be considered. A few of these factors areas follows:
Whether the load will be in tension or
compression 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
The cost of preparing the
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 metal.
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
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.
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 angle, use the correct root
opening, and use the correct root face for the joint. When you follow these principles,
you produce better welds every time. Other standard grooved butt joint designs include the
bevel groove, J-groove, and U-groove, as shown in figure 3-24.
flush corner joint (fig. 3-25, view A) is designed primarily for welding sheet
metal that is 12 gauge or thinner. It is restricted to lighter materials, because deep
penetration is sometimes difficult and the design can support only moderate loads.
The half-open corner joint
(fig. 3-25, view B) is used for welding materials heavier than 12 gauge. Pene-tration
is better than in the flush corner joint, but its use is only recommended for moderate
The full-open corner joint
(fig. 3-25, view C) produces a strong joint, especially when welded on both sides. It
is useful for welding plates of all thicknesses.
square tee joint (fig. 3-26, view A) requires a fillet weld that can be made on one
or both sides. It can be used for light or fairly thick materials. For maximum strength,
considerable weld metal should be placed on each side of the vertical plate.
The single-bevel tee joint
(fig. 3-26, view B) can withstand more severe loadings than the square tee joint,
because of better distribution of stresses. It is generally used on plates of 1/2 inch or
less in thickness and where welding can only be done from one side.
The double-bevel tee joint
(fig. 3-26, view C) is for use where heavy loads are applied and the welding can be
done on both sides of the vertical plate.
single-fillet lap joint (fig. 3-27, view A) is easy to weld, since the filler metal
is simply deposited along the seam. The strength of the weld depends on the size of the
fillet. Metal up to 1/2 inch in thickness and not subject to heavy loads can be welded
using this joint.
When the joint will be
subjected to heavy loads, you should use the double-fillet lap joint (fig. 3-27,
view B). When welded properly, the strength of this joint is very close to the strength of
the base metal.
The flanged edge joint (fig.
3-28, view A) is suitable for plate 1/4 inch or less in thickness and can only sustain
light loads. Edge preparation for this joint may be done, as shown in either views B or C.
by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy