What Is the Throat Thickness of a Weld?

Ships, buildings, and heavy machinery comprise intricate and extensive frameworks, and many kilometers of welded joints make up these frameworks and angles. Fillet welded joints are the most common connections, and the throat is an integral part of the weld. What is the throat thickness of a weld?

The throat thickness of a weld primarily refers to a fillet weld. Typically, it should at least be as thick as the thickness of the metal you are working with, and it can also be any size the designer specifies.

This article looks into the minimum and maximum sizes of a filet weld and the throat thickness of a weld. I also describe the parts of a weld, especially the types of fillet throat.

Maximum and Minimum Sizes of a Fillet Weld?

A filet weld must be sizable enough to carry the applied load, but its specified size should not be excessive to minimize distortion and costs. 

Sometimes, the weld size on the drawing might be unclear, not reported, or the information is missing. You should contact the designer to fill in the blanks in such scenarios. 

Besides that, you can use the guidelines set by the American Welding Society for the minimum filet size required–in AWS D1.1, Table 7.7. For example, 6-mm size for thickness over 12.7 up to 19.0 mm. 

The maximum size of a filet weld will be equal to 0.7 x T, where T is the base metal thickness. Consider the thinner base metal thickness in the case of different thicknesses. You can also get it by subtracting 1.5 mm from the thickness of the thinner member to be joined.

This maximum size should not exceed 1/3rd of the welds’ section’s thickness at the toe. Very large filet welds may cause extremely high residual stresses or unacceptable distortion. Above a certain weld size, it may be more economical to make a T-butt weld.

What Is the Throat Thickness of a Weld?

One aspect of a weld is the throat and its thickness factors into the strength and stability of the weld joint. The two welds with throats are fillet welds and butt welds, but the throat in a fillet weld is more significant.

Throat Thickness of a Fillet Weld

The loads a fillet weld is expected to carry will determine the throat thickness. Even with the designer’s specification, there are still practical limitations concerning minimum and maximum thickness.

Fillet welding is a process that joins two pieces of metals at an angle or when they are perpendicular. Joints welded with this process include T, lap, and corner joints.

You can see these joints in about 80% of all joints made by arc welding, and thus, they are the most common connection in welded fabrication.

One reason for their popularity is how economical they are: compared to groove welds, fillet welds are simple to put together, from edge preparation to fit-up. The components of a fillet weld also don’t need flame cutting.

Welders use fillet welds when bolts are not strong enough and will wear off easily; in welding cross-sections of infrastructure, connecting flanges to pipes. The throat of a fillet weld is the distance from the center of the face to the weld’s root.

Throat Thickness of a Butt Weld

The effective throat thickness of a butt weld determines its size, and it varies based on the type of penetration. In complete penetration, the effective throat thickness is taken as the thickness of the thinner part joined.

For incomplete penetration, it is taken as 7/8th (5/8th for the sake of stress calculation) of the thickness of the thinner part joined. Generally, the throat thickness of a butt joint is the thickness of the parent material.

Butt welding is a process that joins two pieces of metals by placing them end-to-end without overlap. In butt joints, the weld metal stays within the planes of the surfaces. Examples of complete penetration butt welds are double J, double U, double bevel, and double V butt joints. 

The single U, single J, single V, and single bevel butt joints are examples of incomplete penetration butt welds.

How Many Parts Does a Weld Have?

You must become familiar with the terms that describe welds to produce welds that meet the job requirements. Here are some terms that describe the parts of a weld:

  • The weld face is the exposed weld surface, where the torch creates the weld.
  • The weld root is opposite the face—the interface of the weld and base metal at its bottom.
  • The weld toe is the interface of the weld face and base metal.
  • The fusion zone or filler penetration is the zone of base metal melted during the weld.
  • The throat of the weld is the distance from the root of the weld to its center.
  • The weld leg is the distance from the weld toe to the root of the weld.
  • The weld reinforcement is the height of the weld’s portion above the base metal’s surface

For a fillet weld, the root is the part of the deepest penetration, and it is opposite the angle of the hypotenuse. The leg length usually delineates the size of the weld. Leg and throat are often specific for fillet welds, and the two types of the throat are:

  1. The actual throat

It is the distance from the center of its face to the root. It also describes the shortest distance minus any reinforcement between the root and the face.

  1. The theoretical throat

It is a dimension based on the assumption that the root opening equals zero. This is the minimum distance from the beginning of the joint root perpendicular to the hypotenuse of the largest right triangle that can be inscribed within a filet weld cross-section.

If a filet weld is done with an improper leg length, the throat length will be unacceptable, causing a failure in bending loads. Pay attention to the specified dimensions and weld accordingly.

Recent Posts