The weld joint is where two or more metal parts are
joined by welding. The five basic types of weld joints
are the butt, corner, tee, lap, and edge, as shown in figure
3-6.
Figure 3-6.—Basic weld joints.
Figure 3-7.—Root of joint.
Figure 3-8.—The groove face, root face, and root edge of joints.
Figure 3-9.—Bevel angle, groove angle, groove radius, and root opening of joints for welding.
A butt joint is used to join two members aligned in
the same plane (fig. 3-6, view A). This joint is frequently
used in plate, sheet metal, and pipe work. A joint of this
type may be either square or grooved. Some of the
variations of this joint are discussed later in this article.
Corner and tee joints are used to join two members
located at right angles to each other (fig. 3-6, views B
and C). In cross section, the corner joint forms an
L-shape, and the tee joint has the shape of the letter T.
Various joint designs of both types have uses in many
types of metal structures.
A lap joint, as the name implies, is made by lapping
one piece of metal over another (fig. 3-6, view D). This
is one of the strongest types of joints available; however,
for maximum joint efficiency, you should overlap the
metals a minimum of three times the thickness of the
thinnest member you are joining. Lap joints are commonly
used with torch brazing and spot welding applications.
An edge joint is used to join the edges of two or
more members lying in the same plane. Inmost cases,
one of the members is flanged, as shown in figure 3-6,
view E. While this type of joint has some applications
in platework, it is more frequently used in sheet metal
work An edge joint should only be used for joining
metals 1/4 inch or less in thickness that are not subjected
to heavy loads.
The above paragraphs discussed only the five basic
types of joints; however, there are many possible variations.
Later in this article, we'll cover some of these
variations.
Parts of Joints
While there are many variations of joints, the parts
of the joint are described by standard terms. The root of
a joint is that portion of the joint where the metals are
closest to each other. As shown in figure 3-7, the root
may be a point, a line, or an area, when viewed in cross
section. A groove (fig. 3-8) is an opening or space
provided between the edges of the metal parts to be
welded. The groove face is that surface of a metal part
included in the groove, as shown in figure 3-8, view A.
A given joint may have a root face or a root edge. The
root face, also shown in view A, is the portion of the
prepared edge of a part to be joined by a groove weld
that has not been grooved. As you can see, the root face
has relatively small dimensions. The root edge is basically
a root face of zero width, as shown in view B. As
you can see in views C and D of the illustration, the
groove face and the root face are the same metal surfaces
in some joints.
The specified requirements for a particular joint are
expressed in such terms as bevel angle, groove angle,
groove radius, and root opening. A brief description of
each term is shown in figure 3-9.
The bevel angle is the angle formed between the
prepared edge of a member and a plane perpendicular
to the surface of the member.
The groove angle is the total angle of the groove
between the parts to be joined. For example, if the edge
of each of two plates were beveled to an angle of 30
degrees, the groove angle would be 60 degrees. This is
often referred to as the “included angle” between the
parts to be joined by a groove weld.
Figure3-10.—Root penetration and joint penetration of welds.
Figure 3-11.—Weld reinforcement.
The groove radius is the radius used to form the
shape of a J- or U-groove weld joint. It is used only for
special groove joint designs.
The root opening refers to the separation between
the parts to be joined at the root of the joint. It is
sometimes called the “root gap.”
To determine the bevel angle, groove angle, and root
opening for a joint, you must consider the thickness of
the weld material, the type of joint to be made, and the
welding process to be used. As a general rule, gas
welding requires a larger groove angle than manual
metal-arc welding.
The root opening is usually governed by the diameter
of the filler material. This, in turn, depends on the
thickness of the base metal and the welding position.
Figure 3-12.—Simple weld bead.
Having an adequate root opening is essential for root
penetration. Root penetration and joint penetration of welds are
shown in figure 3-10. Root penetration refers to the
depth that a weld extends into the root of the joint. Root
penetration is measured on the center line of the root
cross section. Joint penetration refers to the minimum
depth that a groove (or a flange) weld extends from its
face into a joint, exclusive of weld reinforcement.
As you can see in the figure, the terms, root penetration and
joint penetration, often refer to the same dimension.
This is the case in views A, C, and E of the illustration.
View B, however, shows the difference between root
penetration and joint penetration. View D shows joint
penetration only. Weld reinforcement is a term used to
describe weld metal in excess of the metal necessary to
fill a joint. (See fig. 3-11.)
Figure 3-13.—Standard groove welds.
Types of Welds
There are many types of welds. Some of the common
types you will work with are the bead, groove,
fillet, surfacing, tack, plug, slot, and resistance.
As a beginner, the first type of weld that you learn
to produce is called a weld bead (referred to simply as
a bead). A weld bead is a weld deposit produced by a
single pass with one of the welding processes. An example
of a weld bead is shown in figure 3-12. A weld
bead may be either narrow or wide, depending on the
amount of transverse oscillation (side-to-side movement)
used by the welder. When there is a great deal of
oscillation, the bead is wide; when there is little or no
oscillation, the bead is narrow. A weld bead made without
much weaving motion is often referred to as a
stringer bead. On the other hand, a weld bead made
with side-to-side oscillation is called a weave bead.
Groove welds are simply welds made in the groove
between two members to be joined. The weld is adaptable
to a variety of butt joints, as shown in figure 3-13.
Groove welds may be joined with one or more weld
beads, depending on the thickness of the metal. If two
or more beads are deposited in the groove, the weld is
made with multiple-pass layers, as shown in figure
3-14. As a rule, a multiple-pass layer is made with
stringer beads in manual operations.
When making a multiple-pass weld, a welder uses a buildup or bead sequence,
as shown in figure 3-15. Buildup sequence refers to the
order in which the beads of a multiple-pass weld are
deposited in the joint.
Figure 3-14.—Multiple-pass layers.
Figure 3-15.—Weld layer sequence.
Often welding instructions specify an interpass
temperature. The interpass temperature refers
to the temperature below which the previously
deposited weld metal must be before the next pass may
be started.
Figure 3-16.—Fillet welds.
Figure 3-17.—Surfacing welds.
After the effects of heat buildup on metal are discussed, later
in the article, you will understand the significance of
the buildup sequence and the importance of controlling
the interpass temperature.
A cross-sectional view of a fillet weld (fig. 3-16) is
triangular in shape. This weld is used to join two surfaces
that are at approximately right angles to each other
in a lap, tee, or comer joint.
Surfacing is a welding process used to apply a hard,
wear-resistant layer of metal to surfaces or edges of
worn-out parts. It is one of the most economical methods
of conserving and extending the life of machines, tools,
and construction equipment. As you can see in figure
3-17, a surfacing weld is composed of one or more
stringer or weave beads. Surfacing, sometimes known
as hard surfacing, hardfacing, or wearfacing, is often used to build up
worn shafts, gears, or cutting edges.
A tack weld is a weld made to hold parts of an
assembly in proper alignment temporarily until the final
welds are made. Although the sizes of tack welds are not
specified, they are normally between 1/2 inch to 3/4 inch
in length, but never more than 1 inch in length. In
determining the size and number of tack welds for a
specific job, a welder should consider thicknesses of the
metals being joined and the complexity of the object
being assembled. Heavy weldments on thick metal may
require block tacks. Block tacks are muti-layer tack welds.
Plug and slot welds (fig. 3-18) are welds made
through holes or slots in one member of a lap joint.
These welds are used to join that member to the surface
of another member that has been exposed through the
hole. The hole may or may not be completely filled with
weld metal. These types of welds are often used to join
face-hardened plates from the backer soft side, to install
liner metals inside tanks, or to fill up holes in a plate.
Figure 3-18.—Plug and slot welds.
Resistance welding is a metal fabricating process
in which the fusing temperature is generated at the joint
by the resistance to the flow of an electrical current. This
is accomplished by clamping two or more sheets of
metal between copper electrodes and then passing an
electrical current through them. When the metals are
heated to a melting temperature, forging pressure is
applied through either a manual or automatic means to
weld the pieces together. Spot and seam welding
(fig. 3-19) are two common types of resistance welding
processes.
Spot welding is probably the most commonly used
type of resistance welding. The material to be joined is
placed between two electrodes and pressure is applied.
Next, a charge of electricity is sent from one electrode
through the material to the other electrode. Spot welding
is especially useful in fabricating sheet metal parts.
Figure 3-19.—Spot and seam welds.
Seam welding is like spot welding except that the
spots overlap each other, making a continuous weld seam.
In this process, the metal pieces pass between
roller types of electrodes. As the electrodes revolve, the
current is automatically turned on and off at the speed
for the welder to produce welds that meet the job require-
at which the parts are set to move.
Parts of a Weld
Figure 3-20.—Parts of a groove weld and fillet weld.
To produce welds that meet the job requirements, it is
important to become familiar with the terms used to describe
a weld. Figure 3-20 shows a groove weld and a fillet weld.
The face is the exposed surface of the weld on the side from which
the weld was made. The toe is the junction between the face of the
weld and the base metal. The root of a weld includes the
points at which the back of the weld intersects the base
metal surfaces. When we look at a triangular cross
section of a fillet weld, as shown in view B, the leg is
the portion of the weld from the toe to the root. The
throat is the distance from the root to a point on the face
of the weld along a line perpendicular to the face of the
weld. Theoretically, the face forms a straight line between
the toes.
NOTE: The terms leg and throat apply only to fillet welds.
In determining the size of a groove weld (fig. 3-20,
view A), such factors as the depth of the groove, root
opening, and groove angle must be taken into consideration.
The size of a fillet weld (view B) refers to the length
of the legs of the weld. The two legs are assumed to be
equal in size unless otherwise specified.
A gauge used for determining the size of a weld is known
as a welding micrometer. Figure 3-21 shows how the welding
micrometer is used to determine the various dimensions of a weld.
Figure 3-21.—Using a welding micrometer.
The fusion zone, as
shown in figure 3-22, is the region of the base metal that
is actually melted. The depth of fusion is the distance
that fusion extends into the base metal or previous
welding pass.
Figure 3-22.—Zones in a weld.
Another zone of interest to the welder is the heat-
affected zone, as shown in figure 3-22. This zone includes
that portion of the base metal that has not been
melted; however, the structural or mechanical properties
of the metal have been altered by the welding heat.
Because the mechanical properties of the base metal are
affected by the welding heat, it is important that you
learn techniques to control the heat input. One technique
often used to minimize heat input is the intermittent
weld. We discuss this and other techniques as we progress
through this chapter; but, first we will discuss
some of the considerations that affect the welded joint
design.
Welded Joint Design
The details of a joint, which includes both the geometry
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:
Figure 3-23.—Butt joints.
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 joint
Some of the variations of the welded joint designs and
the efficiency of the joints
Butt 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. Preparation
of the joint is simple, since it only requires matching
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; however,
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.
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 designer
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 article, we discussed the five basic
types of welded joints—butt, corner, tee, lap, and edge.
While there are many variations, every joint you weld
will be one of these basic types.
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.
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.
Figure 3-24.—Additiona1 types of groove welds.
Corner Joints
The 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. Penetration
is better than in the flush corner joint, but its use
is only recommended for moderate loads.
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.
Figure 3-25.—Corner joints.
Tee Joints
The 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.
Figure 3-26.—Tee joints.
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.
Lap Joints
The single-fillet lap joint (fig. 3-27, view A) is easy
to weld, since the filler metal is simply deposited along
The 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. Meteal up to 1/2 inch in thickness and not subject
to heavy loads can be welded using this joint.
Figure 3-27.—Lap joints.
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.
Edge Joints
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
groove welds can be made in all of these positions.
be done, as shown in either views B or C.
Figure 3-28.—Edge joints.
Welding Positions
All welding is done in one of four positions: (1) flat,
(2) horizontal, (3) vertical, or (4) overhead. Fillet or
groove welds can be made in all of these positions.
Figure 3-29 shows the various positions used in plate
welding. The American Welding Society (AWS) identifies
these positions by a number/letter designation; for instance,
the 1G position refers to a groove weld that is to be made
in the flat position.
Figure 3-29.—Welding positions—plate.
Figure 3-30.—Welding positions—pipe.
Here the number 1 is used to indicate the flat position and the G indicates a groove
weld. For a fillet weld made in the flat position, the
number/letter designation is 1F (F for fillet). These
number/letter designations refer to test positions. These
are positions a welder would be required to use during
a welding qualification test.
Because of gravity, the position in which you are
welding affects the flow of molten filler metal. Use the
flat position, if at all possible, because gravity draws the
molten metal downward into the joint making the welding
faster and easier. Horizontal welding is a little more
difficult, because the molten metal tends to sag or flow
downhill onto the lower plate. Vertical welding is done
in a vertical line, usually from bottom to top; however,
on thin material downhill or downhand welding may
be easier. The overhead position is the most difficult
position. Because the weld metal flows downward, this
position requires considerable practice from a welder to
produce good quality welds.
Although the terms flat, horizontal, vertical, and
overhead sufficiently describe the positions for plate
welding, they do not adequately describe pipe welding
positions. In pipe welding, there are four basic test
positions used (fig. 3-30). Notice that the position refers
to the position of the pipe, not the position of welding.
Test position 1G is made with the pipe in the horizontal
position. In this position, the pipe is rolled so that
the welding is done in the flat position with the pipe
rotating under the arc. This position is the most advantageous
of all the pipe welding positions. When you are
welding in the 2G position, the pipe is placed in the
vertical position so the welding can be done in the
horizontal position. The 5G position is similar to the 1G
position in that the axis of the pipe is horizontal.
But, when you are using the 5G position, the pipe is not
turned or rolled during the welding operation; therefore,
the welding is more difficult in this position. When you
are using the 6G position for pipe welding, the axis of
the pipe is at a 45-degree angle with the horizontal and
the pipe is not rolled. Since the pipe is not rolled,
welding has to be done in all the positions— flat, vertical,
horizontal, and overhead. If you can weld pipe in
this position, you can handle all the other welding positions.
NOTE: There is no 3G or 4G test position in pipe
welding. Also, since most pipe welds are groove welds,
they are identified by the letter G.
Welding Heat-Expansion and Contraction
When a piece of metal is heated, the metal expands.
Upon cooling, the metal contracts and tries to resume
its original shape. The effects of this expansion and
contraction are shown in figure 3-31. View A shows a
bar that is not restricted in any way. When the bar is
heated, it is free to expand in all directions. If the bar is
allowed to cool without restraint, it contracts to its
original dimensions.
Figure 3-31.—Effects of expansion and contraction.
When the bar is clamped in a vise (view B) and
heated, expansion is limited to the unrestricted sides of
the bar. As the bar begins to cool, it still contracts
uniformly in all directions. As a result, the bar is now
deformed. It has become narrower and thicker, as shown
in view C.
These same expansion and contraction forces act on
the weld metal and base metal of a welded joint; however,
when two pieces of metal are welded together,
expansion and contraction may not be uniform throughout
all parts of the metal. This is due to the difference in
the temperature from the actual weld joint out to the
edges of the joint. This difference in temperature leads
to internal stresses, distortion, and warpage. Figure 3-32
shows some of the most common difficulties that you
are likely to encounter.
Figure 3-32.—Distortion caused by welding.
When you are welding a single-V butt joint (fig.
3-32, view A), the highest temperature is at the surface
of the molten puddle. The temperature decreases as you
move toward the root of the weld and away from the
weld. Because of the high temperature of the molten
metal, this is where expansion and contraction are greatest.
When the weld begins to cool, the surface of the
weld joint contracts (or shrinks) the most, thus causing
warpage or distortion. View B shows how the same
principles apply to a tee joint. Views C and D show the
distortions caused by welding a bead on one side of a
plate and welding two plates together without proper
tack welds.
All metals, when exposed to heat buildup during
welding, expand in the direction of least resistance.
Conversely, when the metal cools, it contracts by the
same amount; therefore, if you want to prevent or reduce
the distortion of the weldment, you have to use some
method to overcome the effects of heating and cooling.
Welding Distortion-How To Control It
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
The faster a weld is made, the less heat is absorbed
by the base metal. Simply speeding up the welding process
will minimize the amount of heat absorbed by the metal
and lessen distortion.
It is often necessary to use additional welding
techniques 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
weld.
Figure 3-33.—Intermittent welds.
Another technique to control the heat input is the
back-step method (fig. 3-34). When using this technique,
you deposit short weld beads from right to left
along the seam. Back-step welding is very effective
on vertical welds because of the way heat rises. Instead
of starting at the bottom and welding up, start at the top
and work down in small increments. This creates almost zero
distortion when done properly.
Figure 3-34.—Back-step welding.
Preheat the Metal
Expansion and contraction
rates are not uniform in a structure during welding due
to the differences in temperature throughout the metal.
To control the forces of expansion and contraction, you
preheat the entire structure before welding. After the
welding is complete, you allow the structure to cool
slowly.
Limit the Number of Weld Passes
You can keep distortion to a minimum by using as
few weld passes as possible. You should limit the number
of weld passes to the number necessary to meet the
requirements of the job. Stringer beads will increase
the heat input more than weave beads. (See fig. 3-35.)
Figure 3-35.—Weld passes.
Use Jigs and Fixtures
Since holding the metal in a fixed position prevents
excessive movements, the use of jigs and fixtures can
help prevent distortion. A jig or fixture is simply a device
used to hold the metal rigidly in position during the
welding operation.
Allow for Distortion
A simple remedy for the distortion caused by expansion
and contraction is to allow for it during fit-up. To
reduce distortion, you angle the parts to be welded
slightly in the opposite direction in which the contraction
takes place. When the metal cools, contraction
forces pull the pieces back into position. Figure 3-36
shows how distortion can be overcome in both the butt
and tee joints.
Figure 3-36.—Allowing for distortion.
Being a good welder requires more knowledge than just being
able to lay down a good bead. Welding is all about metal and the
more you learn about it, the better your welding projects will
become. In welding, the more you learn, the more you realize that
there is always more you can learn.