Types of Welding Joints: Butt, Lap, T-Joint, Corner & Edge Welds

Welding is an invaluable process for manufacturing parts from metal, allowing almost any shape and configuration of materials to be joined together with strong bonds. One of the reasons welding is so versatile is the wide variety of joints that can be made.

In this guide, we’ll discuss the different types of weld joints, how and when to use them, and the pros and cons of each.

What Are Welding Joints? Definition, Purpose, and Why They Matter

Joining two pieces of metal together with welding sounds simple, but unless you take care to understand and design for the most appropriate weld joints from the outset, it’s easy to end up with an inferior connection, both structurally and aesthetically.

Put simply, a weld joint is the manner in which materials are joined together. Choosing the right type of joint is important, as each has differing strength properties, and some are much easier to accomplish than others in certain situations.

Butt Weld Joints Explained: When to Use Them and Common Applications

A butt weld is when two pieces of flat material are positioned edge to edge; this can be on the same plane or with both pieces following the same shape, such as in the weld seams of a cylindrical tank or vessel.

Butt welds need care and preparation to make them successfully. A thin sheet can easily be burned through if too much welding power is used; conversely, full weld penetration can be difficult to achieve on thicker plates, which is something necessary if the ultimate strength joint is needed.

To mitigate burning through, a backing plate is sometimes used; this also helps to control distortion. To allow full penetration, edge preparation is used by bevelling one, two or all four (both sides) of the plate edges.

Common applications of butt joints include:

• When joining pipes or tubes
• In cylindrical vessels or tanks
• When joining large sheets, such as in shipbuilding or cladding

Lap, T-Joint, and Corner Welds: Strength, Pros, and Use Cases

Lap Joints

Lap joints are often considered in place of butt joints; instead of the two sheets touching on edge, one overlaps the other by an amount. The weld is then made between the edge of one sheet and the face of the other.

Lap joints have the advantage of being easier to make than butt joints but are not as strong due to the inherent stress-raising features. They also tend to require slightly less precision when fitting up, with the overlap allowing small deviations, where gaps would be present in a standard butt.

T-Joints

T joints, or fillet welds, are one of the most common weld joints. T joints have one piece of metal perpendicular to the other (though not always exactly 90°). This allows for a weld joint with little risk of burn-through, but care has to be taken to achieve significant penetration.

T joints can be made between plates, sheets, sections, such as angle or box sections; and pipe. In some cases, the edges of the parts are beveled to allow better penetration – usually when only one side of the joint is accessible.

Corner Joints

When joining sheets at 90°, such as when making square-sided tanks or trays, a corner joint is needed. These typically require quite good fitment between the two pieces to avoid having excessive overlaps or gaps along the joint.

There are a few different ways to arrange a corner joint:

• Open corner – where the two pieces touch only on the corner, essentially creating a fillet weld. This is often the easiest to make if both sides are attached together, i.e., if a sheet has two flanges welded at the corners.
• Half overlap – one sheet is made longer by half the thickness of the other, creating a slightly different type of fillet joint.
• Butt corner joint, or full overlap corner joint – one sheet extends so the edge is flush with the outer face of the other. A groove or weld prep is often added to the outside of this joint to improve strength

Edge Welds: Where They’re Used and Their Limitations

Often used in the mass production of parts such as vehicle body shells and shipping containers, edge welds are where the ends of two sheets are parallel to each other and are welded together along their edges.

While the ends of the sheets are parallel, the rest of the part does not need to be, with flanged corner joints (where one sheet has a 90° bend at the end) or flanged butt joints (where both sheets have a 90° bend at the end) being common.

Not all edge joints will be welded with conventional arc processes; the benefit of edge joints is that they can be spot-welded with either manual or robotic resistance arc welders. These are often called pinch welds in the automotive industry.

One of the main limitations of edge or pinch welds is their stiffness. In order for the whole assembly to have sufficient strength, the panels often need to have stiffening features pressed in beforehand. This is how car body manufacturers create a strong and rigid shell.

Without this, the pre-bending of the end of the sheet can act as a stress raiser if large forces are applied, either collapsing the joint or stretching it out.

How to Choose the Right Type of Welding Joint for Your Project

It is good practice to consider the types of weld joints you will use at the start of a design, making sure that the required strength can be achieved efficiently. There are a few determining factors to consider:

• Strength – if a structure needs to withstand high forces, making joints easy to perform, by either being in the correct orientation, or allowing access to both sides, is a helpful feature, and will result in better welds
• Shape – sometimes a design or application dictates how a joint will look. In these instances, the materials may need to be altered to make the weld joint achievable. For example, not using a very thin sheet where a butt joint is needed.
• Water tightness – when making a tank to contain water or other liquid, an edge weld made by spot welding will not suffice
• Warpage – welding creates intense heat, and after cooling, the metal shrinks, which can cause warping. Selecting the right joint can help mitigate this, e.g., a fillet rather than a butt

Choose Metal Supermarkets for your welding projects.

If you’re planning your next metalworking project, your best bet for all the materials you need is Metal Supermarkets. Stocking everything from thin sheet right up to heavy structural steel, all with a convenient and cost-effective cut-to-length service.

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