What is a Butt Weld?
A butt weld is one of the simplest and versatile types of weld joint designs. The joint is formed simply by placing two pieces of metal end-to-end and then welding along the join.
Importantly, in a butt joint, the surfaces of the workpieces being joined are on the same plane and weld metal remains within the planes of the surfaces. Thus, workpieces are nearly parallel and do not overlap, unlike lap joints, for example.
Depending upon the thickness of the metal pieces, different types of grooves can be prepared. Groove preparation is also called weld edge preparation and is necessary for thicker metals.
Examples of types of grooves, depending upon their shape are V groove, J groove, and U groove. Groove design changes depending upon full penetration or partial penetration weld requirements.
Groove welding can be carried out using different types of welding – whether manual, mechanised or automated processes.
Thin sheets are usually welded without any weld edge preparation, such joints are referred as square butt joint.
Butt joints can be welded using arc welding, resistance welding and high energy beam welding and it can even be part of a brazing operation.
At the start, weld pieces can be held together with a tack weld, which is a temporary joint that ensures components stay in a proper alignment while the butt welding is performed. Pre-heating might be required for joining parts at the butt joint area.
Butt welding is commonly employed in various industry sectors varying from piping systems, automotive, energy, power, etc.
Butt Welding Process
Two pieces of low-grade metal are joined in some way, usually by being fastened to a tabletop or wall fixture. In most cases, the distance between the metals will be around 1/8 inch (3 mm).
The welder then feeds the filler metal into the gap while striking an arc, resulting in a pool of molten metal. After the pool has been carried down the joint’s length, more filler is poured into it in a steady stream.
The space between the metals is there so that the molten metal may reach through the parts being bonded.
Insufficient metal penetration may occur if the space between the two metals is too narrow. Too big of an opening causes a bulky seam on the reverse side.
The degree of penetrability is also affected by the metal’s thickness. One or both of the top edges of metal items larger than 3/16″ are often chamfered.
This may enlarge the opening, facilitating better metal flow across the material’s complete thickness. On the other hand, it may not be required to leave any space at all between the metal pieces if they are extremely thin.
Types of Butt Welding
1. Square Butt Weld
Butt welds with a square groove are the simplest possible joint design. It is utilized on metals up to 3/16 in. thick, and in situations when the weld joint cannot withstand steady stress. Workpieces may be snugly fitted together or have a root opening depending on the desired joint type.
However, the root opening may be essential, depending on the metal and filler used. The edges have not been rounded, beveled, or altered in any manner. They are not rounded off; instead, the weld is placed down the middle of the gap between the butted stock pieces.
Aligning the base metal in the same plane is essential for the successful welding of a square groove. Root opening welding requires uniform gap continuity throughout the weld.
2. Single and Double Bevel Butt Weld
To create a single bevel joint weld, one of the metal plates must be beveled to a predetermined angle or one chosen by the welder. The second metal component keeps its square edge.
Both the metal’s thickness and the size of the finished bead should influence the bevel’s angle. The squared metal piece might be penetrated more easily with the help of a root aperture.
3. Single and Double V Butt Weld
The V groove butt weld design is similar to a double bevel joint. Beveling both pieces of material will create a V-shaped gap between them.
It’s the go-to for butt welds since it allows for maximum penetration and is the most prevalent joint design. This butt weld joint should be used if the material to be welded is thicker than 3/16 inches.
The bevels may be fabricated with little effort.
The edges of metal may be smoothed with a mechanical beveler or a standard angle grinder. Nevertheless, a plasma torch or an oxy-acetylene setup is quicker for beveling edges that are thicker than 3/8 in. Additional filler metal is needed for the V groove joint design.
The cost of the project will rise due to the TIG alloy filler material used if unusual metals are being used. V groove welds are more expensive than single bevel and square butt welds because of the extra time and materials required to prepare and fill the grooves.
These welds are the industry standard and may be found in every welding project. Pipe and structural steel welding are common uses.
4. Single and Double U butt Weld
Unlike the V groove, which has a V-shaped space between its components, the U groove has a U-shaped gap.
The edges need a concave treatment, which is challenging without the right tools. It’s not as common as the V groove, but it’s employed when a price cut is more important than general applicability.
When the metal is prepared for U groove butt welding, less filler material is needed to fill the groove. However, this setup calls for an expert operator.
Because of the joint’s skewed orientation, more dexterity in managing the weld puddle, arc, and filler material is required.
The U groove may also suffer reduced residual stress since less filler metal was deposited. In addition, the weld will be more durable and resistant to deformation and cracking. The cost of any necessary heat therapy to alleviate stress will also be reduced.
5. Single and Double J Butt Weld
The J groove is “half” of a U groove, much as the joint design of a single bevel is “half” of the V groove. It has a similar purpose to the U groove butt weld and is similarly challenging to make and weld.
It takes a high level of expertise and is only cost-effective if the money saved on filler metal is more than the extra money spent on machinery and labor. It’s recommended to weld the J groove butt joint horizontally, with the perpendicular edge on the bottom.
But even then, a skilled welder is required to insert the electrode at an angle into the groove, moving it upward toward the vertical face.
Types of Butt Weld Joints
Butt welds can be used when welding both thin sheet metal and thick metal, but there are specific steps in weld preparation.
The thickness of the metal pieces will indicate whether the butt joints are square or beveled. A square butt weld and a beveled or groove butt weld are two commonly used techniques or types of butt weld.
Square Butt Joints
When welding medium-thickness metals up to 3/16″, you can use a square butt weld, which is done simply by aligning two pieces of metal. The opening between them is typically 1/8 inch, which is enough to allow the molten metal to penetrate both parts.
If the gap is too narrow, the molten metal will sit on top of the surface without properly penetrating both pieces. Meanwhile, if the gap is too broad, there can be a bulky seam on the reverse side.
However, if you are welding thin sheets down to 20 ga., you can use closed square butt joints. In this joint design, two pieces of metal are aligned with little to no gap. Since thin sheets can be vulnerable to high heat, which causes distortion and warping, typically, no filler metal is used.
The heat of the arc itself melts both pieces, creating a method known as fusion welding or autogenous welding.
Groove Butt Welding Joints
Once the metal thickness goes over 3/16″, you can struggle to achieve proper penetration and fusion by simply using a square butt joint design.
These applications will require higher heat and larger electrodes, but it is often impossible to get 100% penetration without some type of square groove being used.
So, when welding thick metal, welders decided to create a root opening by beveling or grooving the edges.
That way, the root opening is reduced to 1/16″ or 1/8″, and it is welded by a root pass with moderate parameters and a welding rod. The rest of the gap is filled with a series of fill passes in an operation known as multi-pass welding.
Depending on the appearance of the sides of the butt weld, the groove butt welds can be:
- Single bevel butt weld
- Double bevel butt weld
- Single J butt weld
- Double J
- Single V
- Double V butt weld
- Single U groove butt weld
- Double U grooves
Each weld joint design is used in various applications, usually specified by Welding Procedure Specification. For example, a V-groove joint design is typically used for medium to thick metals (approximately 1/4).
For even thicker metal plates, welders use U-groove butt welding and J-groove to provide good penetration of welded metal. Whether a fully penetrating or partially penetrating weld is required, different groove configurations must be used.
Application Of Butt Weld Joints
Butt welds find extensive applications across various industries due to their versatility and ability to create strong, seamless connections between metal components.
The widespread use of butt welds across these industries highlights their importance in creating reliable, seamless connections that meet the stringent requirements of different applications. Some common applications include:
- Piping and Pipeline Systems: Butt welds are widely used in the construction of pipelines for transporting liquids and gases. The seamless connection between butt-welded pipe fittings ensures structural integrity and prevents leakage.
- Pressure Vessels: Butt welding is often used in the fabrication of pressure vessels in industries such as chemical processing, oil and gas, and power generation. The welded joints provide the necessary strength to withstand internal pressure.
- Structural Fabrication: In construction and structural engineering, butt welds are used when welding structural steel components, ensuring the stability and integrity of buildings, bridges, and other large structures.
- Automotive Industry: Butt welding is utilized in the assembly of automotive components, including chassis and body structures. It contributes to the overall strength and safety of the vehicle.
- Shipbuilding: Butt welds are prevalent in the shipbuilding industry, where they are employed in the assembly of various metal components, including hulls, decks, and bulkheads.
Advantages Of Butt Weld Joints
- It is the easiest to inspect.
- It has high strength with complete fusion of the butt weld filler material.
- It is applicable to a wide variety of metals.
- It is easy to treat after welding. This is for processes like grinding, polishing, painting, and other machine work.
- It has lesser distortion post-welding.
- The pipe welding done for butt weld joints is cost-effective.
- It is possible to produce many butt welds of varying section sizes and shapes to cover the whole joint region. There are many applications for butt welds, from bicycle wheel rims to railroad ties. The pieces being linked must be as similar as possible. Butt welding may also be used to make miter joints, such as those on welded metal window frames.
- In addition to steels, aluminum, stainless steel, nickel alloys, titanium, etc., the weld may be done on a wide range of other materials.
- An impermeable phase junction is produced by the weld. During the heating phase, any molten metal and impurities generated at the site of collision are forced out into the upset. This eliminates the potential for solidification, porosity, and cracking.
- Welding may be done fully automatically or in a semi-automatic fashion with little human intervention, provided the arc is not struck at an angle. After each blow, the weld may be inspected to see how well it held.
- The butt-welded connection is strong and watertight.
- Strong connections between fittings and pipes in a piping system make it an excellent choice for continuous steel construction in pipes.
- Since the filler material is deposited into the groove during a butt weld, the resulting surface is typically smooth.
- The price of butt-welded pipe fittings is quite inexpensive.
- Butt welds are more efficient because of the space they save.
Disadvantages Of Butt Weld Joints
- It has limited applications owing to the geometry of welding.
- It might be prone to porosity or cracking.
- It might require additional fixturing or backing.
- Burn-through and incomplete penetration are other challenges it may have.
- It is sensitive to the faying surface conditions.