A Guide to the 5 Basic Types of Weld Joints and Tips for Improving Results | MillerWelds

A Guide to the 5 Basic Types of Weld Joints and Tips for Improving Results

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Proper weld joint design is a key factor in making quality welds. From butt joints to T-joints, learn more about the joint types.
Operator MIG welds in a flat position

Weld joint design

There are many factors that contribute to creating a sound weld. Understanding the importance of joint design is one of the crucial factors in producing good-quality welds. 

Proper joint design is based on design specifications outlined in various welding codes or standards used when welding professionally. The joint design determines what type of weld the operator will need to produce to meet the acceptable quality standard. A few examples include T-joints, which require a fillet weld; butt joints requiring a groove weld; lap joints, which require fillet welds; and corner joints, which can be fillet or groove welds. 

Learn more about the five basic types of weld joints recognized by the American Welding Society, and get tips for welding each type to help achieve the best results. 


Image of a butt joint weld

1. Butt joint

This joint type joins two workpieces in the same plane with their edges meeting or with a root opening lying parallel to one another. Butt joints are often used to join plate, pipe, tubing or any other application where a smooth, flush weld face is desired. Welding projects that use this design can include an exhaust system on a car or joining panels for a door.

Butt joints have good mechanical strength when fitted and welded properly. However, if this is not done effectively, it can lead to failures such as distortion or cracking due to residual stresses in the field.

Butt joints can be designed in several ways:

  • They may be welded with backing, which is usually referred to as a backing bar or backing strip, or without a backing material, which is called an open root.
  • When preparing the workpieces for a butt joint, the meeting edges may require no edge preparation. This creates a square joint design when fitted, referred to as a square groove. Common edge preparations for a butt joint are beveled edges, which can be partially beveled or completely beveled throughout the material thickness. Edge preparations usually require a specific bevel angle. One or both workpieces may require these preparations and will create what is known as a V-groove or single bevel.
  • The edges can be in contact with one another, or they can be spaced to a specific tolerance to create a root opening.

The material thickness or application help determine if the edges of a butt joint should be left square or beveled. Beveled edges often create a stronger weld but are more time consuming and require more weld deposit. Square grooves are commonly used on thinner materials where edge preparations are not possible, such as when joining sheet metal or any material that is less than 1/8-inch thick. 

Key tips for butt joints: 

  • For a quality, sound weld, determine whether the edges require any edge preparations or if a square groove joint design will be sufficient for the application.
  • Determine if a root opening should be used or if the workpieces can be welded without one.
  • Ensure that the fit-up of the workpieces is done properly to alleviate any issues while welding and to make the process easier overall.

Image of a corner joint

2. Corner joint

When pieces to be welded are joined at 90 degrees and take the shape of an L, they form a corner joint. These joints are easy to assemble and require little if any edge preparation. They’re often used for projects or applications that require a square frame, such as fabricating a weld table. 

The two types of corner joints are open corner and closed corner. When the edge of one piece lies flush against the edge of another, it’s a closed corner joint. When two edges meet at their corners and there’s an opening where you can see the thickness of each metal, this is an open corner joint. 

Choosing between an open corner joint and a closed corner joint often comes down to the thickness of the material and the strength required for a specific application. 

With open corner joints, you may need to increase your travel speeds when you’re welding on thinner materials to prevent burn-through. Open corner joints create a V shape and may require more weld deposit, depending on the material thickness. 

If you’re welding a closed corner joint, you can grind the weld face to create a smooth transition from the weld to the base material. 

It is important that you properly fit your workpieces when creating a corner joint. If a 90-degree angle is required, make sure it’s square and consider possible distortion once the weld is applied. Depending on how the joint is prepared, the angle can change after welding and lead to distortion. One way to prevent distortion is by creating a jig or fixture that holds the parts in place.

Key tips for corner joints:

  • Increase travel speeds on thinner materials with open corner joints to prevent burn-through. 
  • Ensure proper fit-up to meet required angular dimensions and prevent distortion.

Image of an edge joint

3. Edge joint

An edge joint is created when fit-up of the workpieces leaves the edges parallel or nearly parallel to one another. These joints are often used when the workpieces won’t be subjected to any added stress. An edge joint shouldn’t be used if one or both of the pieces will be subject to impact or any other types of stress. 

There are different types of edge joints depending on how the edges are prepared for welding. They can be left square (square groove), or they can be prepped by grinding, cutting or machining into a V-groove, J-groove or U-groove (similar to how butt joints can be prepared). These preparations improve the weldment by allowing adequate penetration or improving overall weld coverage when welding an edge joint. Also, an edge joint can be welded all around, meaning all sides can be welded for additional joint rigidity.

Edge joints and corner joints have many similarities. A corner joint is typically the outside of the workpieces being welded, while an edge joint can be on the inside of the workpiece. Choosing between an edge joint and a corner joint often comes down to the application needs and material thickness. 

Edge joints may require post-weld grinding to bring the weld flush with the base material if aesthetics are important.

Key tips for edge joints: 

  • Only use these joints in applications that won’t be subject to impact or stress.
  • Use a groove edge preparation to allow adequate penetration or improve the overall weld joint rigidity.
  • Weld an edge joint on all four sides for extra reinforcement.

Image of a Lap joint

4. Lap joint

A lap joint is formed when the surfaces of the two pieces overlap one another. The weld is deposited in the joint where the two intersect. A lap joint exhibits good mechanical properties, especially when both sides of the overlapped pieces are welded, which provides extra reinforcement. 

The amount of overlap needed in the joint is determined by the thickness of the two workpieces. The thicker the material, the more overlap needed. 

Lap joints are very common for joining plates or sheet metal, such as when you’re adding flooring to a vehicle or patching a hole. 

With lap joints, it’s important to make sure there are no gaps between the two workpieces. You want them to be as flush as possible. When welding a lap joint on thinner materials like sheet metal, reduce your amperage and use a faster travel speed to avoid distortion and burn-through. 

When choosing between a butt joint or a lap joint, consider that a butt joint will result in a more flush contour, leaving the workpieces in the same plane. Lap joints can provide more strength in higher stressed areas, but the joints are more noticeable and do not result in a flush contour.  

Key tips for lap joints: 

  • Weld both sides of the overlapped workpieces for additional rigidity.
  • Use more of an overlap between the two pieces when welding thicker materials. 
  • Before welding, make sure the two pieces are as flush as possible.

Image of a T joint

5. T-joint

A T-joint is created when the edges of your two workpieces meet at approximately 90 degrees and take the shape of a T. The edge of one workpiece is welded to the flat surface of another. T-joints possess good mechanical strength, especially when welded from both sides. They’re found in many fabrication applications, including structural steel, tubing and equipment applications. 

T-joints generally require little or no joint preparation and are easily welded when the correct parameters and techniques are used. The edges of the joint may be left unaltered, or they may be prepped by cutting, machining or grinding.

When welding a T-joint, it is important to place the weld on the same side of the joint that will be subject to any type of stress. Impact or load from the opposite side of the joint could cause the weld to fail. To avoid this, you can weld both sides to achieve maximum strength or when stress will be applied from both directions. 

T-joints are the most common joint design in all welding applications. They can be welded fairly easily in the flat, horizontal, vertical or overhead position, while other joint designs can be more difficult to weld out of position. 

When welding a T-joint with a 90-degree angle, it’s best to split the difference using a 45-degree work angle to ensure you will achieve proper penetration on both workpieces. If you’re welding dissimilar metal thicknesses using a T-joint, focus more of your weld onto the thicker piece of material.

Key tips for T-joints: 

  • Weld the joint from both sides to improve strength. 
  • Place the weld on the same side of the joint that is subject to stress.
  • Use a 45-degree work angle to ensure proper penetration on both workpieces being welded.

Understanding the types of weld joints 

Some joint designs are stronger and can undergo more stress than others, so it’s important to know the differences and choose the best design for your application needs. Knowing the basics about each type of weld joint and when it is typically used can help ensure you’re using the most effective joint design and the right techniques in your welding projects. Read this article to learn more about the basic welding positions