Welding Joint: Definition, Types, Pros, and Cons

What is Welding Joint?

A welding joint is a point or edge where two or more pieces of metal or plastic are joined together. They are formed by welding two or more workpieces (metal or plastic) according to a particular geometry. There are five types of joints referred to by the American Welding Society: butt, corner, edge, lap, and tee.

These configurations may have various configurations at the joint where actual welding can occur.

Welding is a complex craft that requires patience, an eye for detail, and creativity. In order to do their job successfully, welders must have an in-depth understanding of the various techniques and practices used in the industry, which includes welding joint types.

The term “weld joint design” refers to the way metal parts are joined or aligned with one another. The design of each joint affects the quality and cost of the finished weld. Selecting the most suitable joint design for a welding job requires special attention and skill.

Types of Welding Joint

According to AWS, there are five basic welding joint types that are commonly used in the industry:

  • Butt joint
  • Tee joint
  • Corner joint
  • Lap joint
  • Edge joint
Type of Welding joint

1. Butt Joint Welding

A butt joint is a joint where two pieces of metal are put together in the same plane and the side of each metal is joined by welding. A butt weld is the most common type of joint used in the manufacture of structures and piping systems. It’s pretty easy to prepare and there are many different variations that can be applied to get the result you want.

Butt welds are made in different ways, each serving a different purpose. Different factors are the shape of the groove, the layering, and the width of the gap. Below are some typical examples of butt weld joints.

  • Square
  • Single bevel
  • Double bevel
  • Single J
  • Double J
  • Single V
  • Double V
  • Single U
  • Double U grooves

The area of the metal’s surface that is melted during the welding process is called the faying surface. The faying surface can be shaped before welding to increase the weld’s strength, which is called edge preparation. The edge preparation may be the same on both members of the butt joint, or each side can be shaped differently.

Reasons for preparing the faying surfaces for welding include the following:

  • Codes and standards
  • Metals
  • Deeper weld penetration
  • Smooth appearance
  • Increased strength

In some cases, the exact size, shape, and angle can be specified for a groove. If exact dimensions are not given, the groove can be made to the necessary size. However, it’s important to remember that the wider the groove, the more welding it will require to complete.

As the metal becomes thicker, you must change the joint design to ensure a sound weld. On thin sections, it is often possible to make full penetration welds using a square butt joint. When welding on a thick plate or pipe, it is often impossible for the welder to get 100% penetration without some type of groove being used.

When it comes to butt joints, commonly occurring defects may include burning through, porosity, cracking, or incomplete penetration. However, these can be avoided by modifying the welding variables.

2. Tee Joint Welding

Tee welding joints are formed when two pieces intersect at a 90° angle. This results in the edges coming together in the center of a plate or component in a ‘T’ shape. Tee joints are considered to be a type of fillet weld, and they can also be formed when a tube or pipe is welded onto a base plate.

 With this type of weld, it’s important to always ensure there is effective penetration into the roof of the weld. There are a handful of welding styles that can be used to create a tee joint:

  • Plug weld
  • Slot weld
  • Bevel-groove weld
  • Fillet weld
  • J-groove weld
  • Melt-through weld
  • Flare-bevel-groove weld

Tee joints are not usually prepared with grooves unless the base metal is thick and welding on both sides cannot withstand the load the joint must support. A common defect that occurs with tee joints is lamellar tearing which happens due to restriction experienced by the joint. To prevent this, welders will often place a stopper to prevent joint deformities.

3. Corner Joint Welding

Corner joints have similarities to tee welding joints. However, the difference is the location of where the metal is positioned. In the tee joint, it’s placed in the middle, whereas corner joints meet in the ‘corner’ in either an open or closed manner forming an ‘L’ shape.

These types of joints are among some of the most common in the sheet metal industry, such as in the construction of frames, boxes, and other applications. There are two ways of fitting up an outside corner joint either it forms a V-groove (A) or forms a square butt joint (B), as seen in the diagram below.

The styles used for creating corner joints include V-groove, J-groove, U-groove, spot, edge, fillet, corner-flange, bevel-groove, flare-V-groove, and square-groove or butt.

4. Lap Joint Welding

Lap welding joints are essentially a modified version of the butt joint. They are formed when two pieces of metal are placed in an overlapping pattern on top of each other. They are most commonly used to join two pieces with differing thicknesses together. Welds can be made on one or both sides.

Lap joints are rarely used on thicker materials and are commonly used for sheet metal. Potential drawbacks to this type of welding joint include lamellar tearing or corrosion due to overlapping materials. However, as with anything, this can be prevented by using the correct techniques and modifying variables as necessary.

5. Edge Joint Welding

In an edge joint, the metal surfaces are placed together so that the edges are even. One or both plates may be formed by bending them at an angle.

The purpose of a weld joint is to join parts together so that the stresses are distributed. The forces causing stresses in welded joints are tensile, compression, bending, torsion and shear, as seen in the image below.

The ability of a welded joint to withstand these forces depends upon both the joint design and the weld integrity. Some joints can withstand certain types of forces better than others.

The welding process to be used as a major effect on the selection of the joint design. Each welding process has characteristics that affect its performance. The rate of travel, penetration, deposition rate, and heat input also affect the welds used on some joint designs. The following styles are applicable for edge joints:

  • U-groove
  • V-groove
  • J-groove
  • Corner-flange
  • Bevel-groove
  • Square-groove
  • Edge-flange

Due to overlapping parts, this type of joint is more prone to corrosion. Welders must keep in mind other defects like slag inclusion, lack of fusion, and porosity, which can also occur.

Advantages of Welding Joint

  • The welded joint is a permanent joint. In principle, permanent joints do not allow the dismantling of jointed parts without damaging them. This allows jointed components to be held in place without failure or leakage.
  • Superior joint strength. The strength of the sound weld joint is similar to that of the higher-level components. eventually even more. As a rule of thumb, the strength of the welded joint is considered 100%.
  • Leak-proof joining. The welded joint provides an absolutely leak-proof joining when the welding is done properly.
  • There is no need to drill holes in the parent parts. In the case of a riveted joint (another permanent joining process), holes are required to drill the parent components, which greatly reduces the strength of the parent components. There is no need to drill such a hole on the parent parts for the welded joint, with the exception of edge preparations (which are permanently filled with filler metal so that the actual strength is not reduced).
  • High load capacity. Since the strength of the welded joint is similar to that of the parent parts, the load-bearing capacity of the welded components remains unchanged before and after joining.
  • Possibility to change the mechanical properties. By using suitable filler material, protective gas, and an electrode coating, various mechanical properties of the weld bead can be improved to the desired level.
  • Welded assemblies are lighter. Compared to riveted joints (which require additional straps, rivets, etc.), welded joints are lightweight.
  • Different shapes can be connected. The ability to join different shapes including plates, bars, sheets, etc. makes the welding process unique among different joining processes.
  • Dissimilar metal joining. Joining two or more dissimilar metals are also possible, with or without the application of filler. However, dissimilar metal joining needs extra precautions.
  • Possibility of joining plastics. Other than metals, plastics can also be welded in various ways.

Disadvantages of Welding Joint

  • Change in metallurgical properties. Since the base plates are heated to an elevated temperature and then cooled to room temperature during welding, metallurgical changes take place around the weld. Most of the time, such changes are undesirable.
  • Residual stress generation. Due to the uneven heating and cooling, residual stress is created in the welded structures. Such residual stress is usually undesirable as it greatly reduces the load-bearing capacity of welded structures.
  • Component distortion. Uneven heating and cooling are also associated with distortion of the jointed structures, leading to dimensional inaccuracies and thus rejected parts.
  • Poor vibration sustaining capability. Welded joints are prone to vibration and therefore fail with long-term use under vibration. In such a scenario, riveted joints are preferable.
  • Inspection is difficult. Checking for the presence of defects in welded joints is a somewhat difficult task and requires sophisticated testing methods (non-destructive testing) to inspect, which are usually more expensive.

Application of Welding

The welding is widely used for the fabrication of pressure vessels, bridges, building structures, aircraft and space crafts, railway coaches, and general applications besides shipbuilding, automobile, electrical, electronic, and defense industries, laying of pipelines and railway tracks, and nuclear installations.

  • Fabrication of sheet metal.
  • Automobile and aircraft industries.
  • Joining ferrous and non-ferrous metals.
  • Joining thin metals.

FAQs.

What is a Welding joint?

A welding joint is a point or edge where two or more pieces of metal or plastic are joined together. They are formed by welding two or more workpieces (metal or plastic) according to a particular geometry. There are five types of joints referred to by the American Welding Society: butt, corner, edge, lap, and tee.

What are the types of welding joints?

There are five basic welding joint types:
1. Butt joint.
2. Tee joint.
3. Corner joint.
4. Lap joint.
5. Edge joint.

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