What is a Welding Joint?
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.
According to the American Welding Society (AWS), a joint can be defined as “the way materials fit together”. The applications of welding are endless and different tasks require different types of welds and joints.
There are five main types of welded joints, each meeting the needs and forces of different applications. Read on to learn more about each area and how it can affect a career in that area:
Different 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.
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
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.
- 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
- 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 burn through, porosity, cracking or incomplete penetration. However, these can be avoided by modifying the welding variables.
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 groove, 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.
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.
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 joint 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 correct technique and modifying variables as necessary.
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 has 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:
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
- They are lighter
- The cost of the welded joint is lower
- They are tight and leak proof
- Their production time is less
- There is no problem with stress concentration
- It has a good appearance
- Their strength is high
- It is easy to do in many parts which are difficult to riveting
- As no hole is required for welding, hence no reduction of area. So structural members are more effective in taking the load.
- In welding filler plates, gusseted plates, connecting angles, etc, are not used, which leads to reduced overall weight of the structure.
- Welded joints are more economical as less labor and less material is required.
- The welded structures are usually lighter than riveted structures.
- The welded joints provide maximum efficiency which is not possible in the case of riveted joints.
- In welded connections, the tension members are not weakened, whereas riveted are weak.
- The welded joints look better and more smooth in appearance than the bulky riveted/butted joints.
- The speed of fabrication is faster in comparison with the riveted joints.
- Complete rigid joints can be provided with the welding process.
- The alternation and addition to the existing structure are easy.
- No noise is produced during the welding process as in the case of riveting.
- The welding process requires less workspace in comparison to riveting.
- Any space of joint can be made with ease.
- A welded joint has great strength. Often a welded joint has the strength of the parent metal itself.
- Sometimes, the members are of such a shape (i.e., circular steel pipes) that they afford difficulty for riveting. But they can be easily welded.
- It is possible to weld any part of a structure at any point. But riveting requires enough clearance.
Disadvantages of Welding
- Welded joints are more brittle and therefore their fatigue strength is less than the members joined.
- Due to uneven heating & cooling of the members during the welding, the members may distort resulting in additional stresses.
- Skilled labor, supervision, and electricity are required for welding.
- No provision for expansion and contraction is kept in welded connection & therefore, there is the possibility of cracks.
- The inspection of welding work is more difficult and costlier than riveting work.
- Defects like internal air pockets, slag inclusion, and incomplete penetration are difficult to detect.
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.
Friquantaly Ask Questions
What is Welding Joint?
Welding is a complex craft that requires patience, an eye for detail, and creativity. 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.
What are the types of welding joints?
There are five basic welding joint types:
- Butt joint.
- Tee joint.
- Corner joint.
- Lap joint.
- Edge joint.
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