What Is A Butt Weld?

What is a butt weld

A butt weld is formed when two pieces of metal are laid side by side and are joined along one edge.

Butt Weld


  • Fitting pipes to themselves
  • Fittings
  • Flanges
  • Valves

The butt weld is also called a square-groove and is a common joint in welding. The two pieces of metal are laid side by side, but not overlapping, and are welded down one edge. A gap of around 1/8” is usually left between the workpieces and these can be held in place with a tack weld to keep them in the right place while you weld. This small gap allows the filler metal to flow between the metals to complete the weld properly.

Butt welds can be created using groove welds.

Groove Welds

If you are working with thicker metals, the pieces to be joined must be prepared to ensure the best weld. Part of the edges of the workpieces can be beveled out to create an angled edge, which will allow the filler metal to correctly penetrate the groove which is created. Without this, the filler metal would have a smaller area and the weld would not take.

There are several different types of groove weld, and the one you choose will depend on the type of metal, the thickness and what the intended joint will be used for.

  • Square-groove butt weld. This is used when both pieces are flat on the edge to be joined. The weld is completed across the two pieces, and some will go in to the groove to seal them. Ideally it is used where metals are 3/16 of an inch thick or less. Although strong, because of the nature of the weld, it should not be used where the finished weld will be subjected to shock loads.

For thicker metals you will need beveled grooves.

  • Single Bevel-groove: This is where one piece of metal is cut to an angle of 40-50 degrees
  • V-groove: The edges of both workpieces are beveled to form the shape of a ‘V’. This is usually used on frames, and the angle is between 25- 30 degrees.
  • U-groove: Both edges are beveled, but in this case they form the shape of a ‘U’. The angle is a lot smaller at between 8-12 degrees.
  • J-groove: Only one edge is beveled in a curved angle of 10-20 degrees.
  • Flare V-groove: This is where 2 round edges are welded together, such as joining pipes.
  • Flare bevel-groove: This is used when joining a round surface, such as a pipe, to a square one.

As well as butt joints, there are other types of joints used in welding

Tee Joints

Tee joints are created when two pieces of metal form a ‘T’ shape. One piece is placed in the middle of the other, at a 90 degree angle. This type of joint is also a form of fillet weld.

Tee joints don’t usually require a groove as they are welded on both sides. If the joint will be used to withstand a heavy load, then a groove joint may be a better option. These joints are used for:

  • Attaching a pipe to a base

Lap Joints

These joints are used when welding together two pieces of metal of different thicknesses, or where metals overlap. The weld can be completed on both sides, and is also a type of fillet weld. This type of weld is usually used on sheet metals, rather than thicker ones.

Lap joints can be used for:

  • Cabinet and frame making
  • Table making
  • Automation processes

Corner Joint

This is a common weld. It is used when two pieces of metal join at right angles, and the weld is completed on the outer edge. The resultant joint will be in the shape of an ‘L’. Due to the nature of this weld, it can be tricky to find a place to rest your hands to control the weld.

Corner joints have many uses including:

  • Boxes
  • Frames

Edge joint

This is used when the metals have flanging edges. The two pieces are usually placed side by side to each other, and the weld is completed along one edge. It can be necessary to bend one of the plates as it’s best to create edges which are even so that the stress is evenly distributed.

Uses for edge joints:

  • Mufflers
  • Thin pieces of sheet metal

Frequently Asked Questions:

How do I know which joint to use?

The joint will be based on the metals you are joining and the application they will be used for. Experience will teach you the best method to use, such as which groove joint you will need.

What’s the best welding process for a butt weld?

There is no right or wrong process to use for a butt weld, and you can use Arc welding, resistance welding or high energy beam. The most important factor is knowing how to adjust the weld for the strongest joint and to make sure that the filler metal flows correctly in to the joint.

What if the gap in my butt weld is too large?

It’s very important to make sure you have the right gap when you complete your gap weld. If it’s too large, too much filler will enter and this will likely go straight through the gap, whereas too small a gap will mean not enough filler metal will get in. This would mean your joint may not be strong enough for its intended purpose.


Butt joints are considered an easy joint to weld, but there is a lot to learn. Before you begin you will need to check the intended load on the joint so you can work out how to complete it. The correct groove weld will make a big difference to the strength and appearance of your weld.

If in doubt, try a practice weld, to make sure that the filler metal flows correctly, just where you need it.

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