Types of Welding Joints and Welds – Color Graphics
Get up to speed on the main types of welding joints, the common types of welds, their parts, and usage.
For welders first getting a handle on weld joint design—how pieces of metal are put together or aligned with each other for welding—it’s important to distinguish between the joint and the weld.
Types of Welding Joints
Welders describe the point where two or more base metals meet for welding as the weld joint. The five main types of welding joints are:
- Butt joints
- Lap joints
- Tee joints
- Corner joints
- Edge joints
Use the butt joint to weld materials aligned in the same plane. It works with plate, sheet metal, and pipework. This joint can be square or grooved.
Square Butt Joint
Best for metals 3/16 inch or less in thickness, the square butt joint is reasonably strong when not under fatigue or impact loads (Figure 1 View A).
Single-V Butt Joint
For more strength welding metals of 1/4 to 3/4 inch in thickness, use a single-grooved butt joint design (Figure 1 View B). Use a groove angle (approximately 60 degrees for plate) that allows the electrode into the joint for good penetration.
Double-V Butt Joint
You can use the double-v butt joint when welding metals thicker than 3/4 inch, or on thinner plates for extra strength (Figure 1 View C).
Other Butt Joint Designs
Other standard, but less used, grooved butt types of welding joints include the single and double-bevel, single and double-J, and the single and double-U (Figure 2).
Made by overlapping one piece of metal over another, the lap joint can be one of the strongest types of joints. Overlapping the metals at least three times the thickness of the thinnest member results in the most efficient joint (strongest relative to the base metal).
Single-Fillet Lap Joint
The single-fillet lap joint (Figure 3 View A) depends on the size of the weld for its strength.
This weld joint is used for metal up to 1/2 inch thick that isn’t subject to heavy loads.
Double-Fillet Lap Joint
When properly welded, the double-fillet lap joint is nearly as strong as the base metal itself. It’s ideal for heavy loads (Figure 3 View B).
To weld two pieces at approximately right angles, use the tee joint (or t-joint). It forms the letter “T” and is used in various joint designs. You’ll find the tee joint in many types of welded metal structures.
Square Tee Joint
Used to weld light or moderately thick materials, the square tee joint (Figure 4 View A) needs a fillet weld on one or both sides.
Single-Bevel Tee Joint
With better stress distribution, the single-bevel tee joint (Figure 4 View B) can handle more severe loads. Use this joint with plates 1/2 inch thick or less, when welding is possible from only one side.
Double-Bevel Tee Joint
The double-bevel tee joint handles heavy loads when welded from both sides (Figure 4 View C).
Similar to the tee joint, the corner joint forms an L-shape.
Flush Corner Joint
Best used for welding 12-gauge or thinner sheet metal, the flush corner joint design can support only moderate loads. Good weld penetration is often difficult with this type of joint (Figure 5 View A).
Half-Open Corner Joint
Because penetration is better, use the half-open corner (Figure 5 View B) joint for welding members heavier than 12-gauge. This joint supports moderate loads.
Full-Open Corner Joint
To produce a strong joint with plates of all sizes, especially when welding from both sides, use the full-open corner joint (Figure 5 View C).
A joint between the edges of two or more parallel or nearly parallel members. Often with this type of joint, one of the pieces is flanged.
Although found in plate work, this joint is more common in sheet metal work. Use an edge type of welding joint only for joining members 1/4 inch or less that are not subject to heavy stresses.
Flanged Edge Joints
The flanged edge joint (Figure 6 View A) is suited for plate 1/4 inch thick or less, under light loads.
Figure 6 View B and C show joint preparation of thin and thick workpieces.
Parts of Joints
You’ll want to become familiar with the standard terms used to describe the parts of a joint.
Root of a Joint
The root of a joint is the narrowest point in the gap between two members to be welded, or the point in the gap furthest removed from the electrode. Generally, these points are the same.
As shown in Figure 7, the root may be a point, a line, or an area when viewed in a cross section.
Groove of a Joint
An opening or channel in the surface of a part or between two components which provides space to contain a weld is called the groove of a joint.
The groove face is the surface of a member included in the groove (Figure 8 View A).
A joint may have a root face or a root edge.
The root face (Figure 8 View A), is the area of a grooved edge that’s not grooved. It usually has small, but measurable dimensions.
When the groove face extends the full thickness of the member, leaving the root face at essentially zero width, it’s called a root edge (Figure 8 View B).
Sometimes, the groove face and the root face occupy the same surfaces. (Figure 8 Views C and D).
Welders describe the individual requirements for a specific joint with terms such as bevel angle, groove angle, groove radius, and root opening.
The angle formed between the prepared edge of the base metal and a plane perpendicular to the surface of the base metal is the bevel angle (Figure 9) This angle refers to the metal that has been removed.
The groove angle is the total angle of the groove between the materials to be joined. So, when butted together, the edges of two plates, each with a 45-degree bevel, create a total groove angle of 90 degrees. You’ll also see this called the included angle.
Used for special groove joint designs, the radius used to form the shape of a j- or u-groove weld joint is the groove radius (Figure 10).
The separation between the members to be joined at the root of the joint is the root opening, or root gap.
The specifications for bevel angle, groove angle, and root opening for a joint are based on the welding process, the base metal thickness, and the type of welding joint used. Gas welding usually requires a larger groove angle than arc welding.
The root opening must accommodate the diameter of the filler material, which is chosen based on the base metal thickness and the welding position. An adequate root opening is important for proper root penetration.
Root penetration refers to the distance the weld metal extends into the root joint. It’s measured on the centerline of the root cross section (Figure 11).
The minimum depth a groove or flange weld extends from its face into a joint, exclusive of reinforcement.
Joint penetration may include root penetration as in Views A, C, and E.
However, see how View B shows the difference between root penetration and joint penetration, and View D shows joint penetration only.
Weld reinforcement describes the metal that exceeds the quantity needed to fill a joint at the face or root. (Figure 12).
Types of Welds
While there are many types of welds, the most common you’ll run across are bead, fillet, groove, surfacing, tack, plug, slot, and resistance.
Most of us start out learning a basic weld bead. Also known as a bead, it’s a simple single-pass type of weld on a base metal (Figure 13).
Make a narrow stringer bead by using little to no side-to-side weaving motion. You create the wider weave bead with greater side-to-side motion.
Made in the groove between two members of a work-piece, groove welds (Figure 14) are adaptable to many butt joints of differing thicknesses.
When a groove needs two or more beads to fill it, it’s a multiple-pass, or multi-pass weld. Multiple pass layers (Figure 15) are usually made with narrow stringer beads in a manual process.
When making this type of weld, the buildup sequence specifies the order to lay each bead (Figure 16).
To control the effect of accumulated heat on metal materials, multi-pass welding instructions may specify an interpass temperature. This is the minimum, or maximum, temperature the deposited weld metal should reach before starting the next pass.
Used to join two surfaces at approximately at right angles (90 degrees), the fillet weld forms a triangle when viewed in cross section. The lap, tee, and corner joints are types of fillet welds (Figure 17).
A surfacing weld adds filler metal material to a base metal substrate to get desired properties or dimensions (Figure 18).
Hardfacing, or wearfacing, is a surfacing variation to deposit material on a part to reduce wear or loss of material by abrasion, impact, erosion, galling, and cavitation.
This type of weld consists of one or more stringer or weave beads.
A surfacing weld is a cost-effective method to extend the life of machines, tools, and equipment, and is especially useful in the construction industry.
Plug & Slot Welds
A weld made through holes in one member of a lap joint is a plug weld. When the holes are elongated, it’s called a slot weld (Figure 19).
Depending on the work, the holes may or may not be totally filled with filler material. Often, this type of weld attaches face-hardened plates to softer backer material or to install liner metals inside tanks.
When the fusing temperature is generated at the joint by resistance to the flow of an electrical current through the workpiece, it’s a resistance weld.
This happens by passing an electrical current through two or more sheets of metal clamped between copper electrodes. Once the temperature reaches the melting point, applied pressure welds the pieces together (Figure 20).
One common variation is resistance spot welding (RSW) which places a series of spot welds along the joint (Figure 21).
Another style, resistance seam welding (RSEW) used in commercial manufacturing, applies a series of tight welds while feeding materials through electrode wheels.
On thin sheet metal lap joints, arc welders can create a spot weld (Figure 22). A short arc on one surface burns through to the other, fusing the pieces together.
It’s not as neat as RSW, because this type of weld leaves a small nugget on the metal surface.
A tack weld is a weak, temporary weld used to hold metal in place until it’s welded (Figure 22). Size varies by thickness of metals, but tack welds should be small and uniform to minimize its effect on the final weld.
Parts of Welds
Some terms to describe a weld may apply to multiple joint assemblies, while others are unique.
Face — the exposed surface of the base metal where the weld is made.
Toe — the junction between the face of the weld and the base metal.
Root — the points at which the back of the weld intersects the base metal surfaces.
Leg — the portion of the weld from the toe to the root when looking at a triangular cross section of a fillet weld.
Throat — the distance from the root to a point on the face of the weld along a line perpendicular to the face of the weld. In theory, the face forms a straight line between the toes.
NOTE: The terms leg and throat apply only to fillet welds.
Parts of a Groove Weld
- Root Opening: The separation between the members to be joined at the root of the joint.
- Root Face: Groove face next to the root of the joint.
- Groove Face: The surface of a member included in the groove.
- Bevel Angle: The angle formed between the prepared edge of a member and a plane perpendicular to the surface of the member.
- Groove Angle: The total included angle of the groove between the parts to be joined.
- Size of Weld: The joint penetration (depth of bevel plus the root penetration when specified). The size of a groove weld and its effective throat are the same.
- Plate Thickness: Thickness of plate welded.
Parts of a Fillet Weld
- Actual Throat of a Fillet Weld: The shortest distance from the root of the fillet weld to its face.
- Leg of a Fillet Weld: The distance from the root of the joint to the toe of the fillet weld.
- Root of a Weld: The points at which the back of the weld intersects the base metal surfaces.
- Toe of a Weld: The junction between the face of a weld and the base metal.
- Face of Weld: The exposed surface of a weld on the welded side.
- Depth of Fusion: The distance that fusion extends into the base metal, or previous pass, from the surface melted during welding.
- Size of Welds: Leg length of the fillet.
When determining the size of a groove weld (Figure 23), the depth of the groove, root opening, and groove angle must all be considered.
The size of a fillet weld (Figure 24) is the length of the legs of the weld. Assume the legs are equal, unless otherwise noted.
Many styles and types of welding gauges exist to prepare material for welding and check the completed weld. Here’s an example of a welding gauge kit.
Welders use a few more terms used to describe areas of the weld.
The heat-affected zone (HAZ) (Figure 25) is the portion of a base metal that has not melted, but has changed because of the heat of welding. The HAZ is between the weld deposit and the unaffected base metal. The physical make-up or mechanical properties of this zone are different after welding.
Fusion describes the melting together of base and/or filler metal. The fusion zone is the region of the base metal that melted during welding (Figure 25).
Because welding heat affects the structural properties of the base metal, controlling heat is essential to a good weld.
Plate Welding Positions
The American Welding Society (AWS) divides plate welding into four basic positions: (1) flat, (2) horizontal, (3) vertical, and (4) overhead.
You can identify a weld by the number showing welding position, followed by letter “G” for a groove weld, or “F” for a fillet weld (Figure 26). For example, a vertical groove weld is a “3G” weld.