How Do You Choose Weld Size?

Measurements, dimensions, and calculations are a very essential parts of welding. With almost all measurements having similar levels of complexity, it’s very easy to mix them up. For weld size, which is an important part of welding, how do you determine weld size?

You can always calculate the weld size of your fillet weld if you know the plate thickness of the thinnest leg of the weld. If the plate thickness is unknown, you can always fall back to the default 6mm fillet weld size, with the minimum and maximum possible values being 3mm and 0.7t respectively.

In this article, you’ll learn if you should calculate and note your weld sizes, instead of mostly leaving them to the designer. You’ll also learn how to determine the weld size, as well as some industry standard figures relating to weld sizes.

What’s Fillet Weld Size?

If you’ve ever wondered how the weld size value came into being, it’s simply one of the defining features of a fillet weld. Therefore, it would take a solid understanding of the fillet weld concept to have a solid go at describing weld size.

If you don’t know already, fillet welding is a common procedure used to join two metals together at a perpendicular or 45% angle. The result of a fillet weld is usually a T-shaped or L-shaped metal, formed from the two conjoined edges.

Fillet weld is responsible for about 80% of all welds in the industry, which is an overwhelmingly high number, considering that there are other options too. The best alternative for fillet welding is butt welding, a procedure that should compete with fillet welds. However, it seems obvious that one has ready dominated the industry.

The weld size is a popular way to determine the strength and quality of a weld across different welding standards. Since this section is only about fillet welds, it’s only logical to discuss fillet weld sizes only.

In a fillet weld, the sizes are the same as the value of the leg length. To determine the quality of your fillet weld, you only need to measure or calculate the leg length and compare it to the industry standard.

The definition of fillet weld sizes given above is based on the assumption that both of the leg sizes are equal. If there are any disparities in the leg sizes for both legs, the smaller or thinner legs are always used as the authentic weld size.

Since we’ve established what a fillet weld means and how you can calculate the size of a fillet weld, it’s time to explore the other types of welding that also deal with weld sizes and how to determine the best value for weld sizes.

What Is Butt Weld Size?

Predictably, the fillet weld isn’t the only weld type that can have a weld size. There is also the butt welding joint, which is most commonly used in welded pipe systems, and it also has a definite value for the weld size.

Unlike a fillet weld, a butt weld is created when two metals are joined side to side from their ends, seemingly explaining the weird name choice. In a butt joint, the materials are almost always parallel, and they’re not arranged in a perpendicular, unlike the fillet weld.

Instead of the shape of the resulting weld, butt welds are typically referred to using the shape of their grooves. The groove can either be J-shaped, U-shaped or V-shaped, depending on the thickness of the metal.

Instead, most welders refer to the different types of fillet welds by their shapes, which include L-shaped and T-shaped welds. However, the industry standard is referring to types of fillet welds using concave, convex, or miter welds.

Butt welds are preferred over fillet welds in some applications due to their ease of machination and inspection, as well as their strength and durability. However, it usually required backing, and it wasn’t designed to be as flexible as some other alternatives.

In short, butt weld is fillet weld, but on the same vertical plane. If the joining surfaces are perpendicular to each other, it’s most likely a fillet weld.

How Do You Choose Fillet Weld Size

The size of a fillet weld is generally denoted by its leg length value. There are industry standard values for the minimum and maximum fillet weld sizes, but it’s important to recalculate to determine the precise values for your specific task.

The minimum size only signifies the lowest you can go in any circumstance, while the maximum size is an effective limit to avoid laughable errors. If the designer doesn’t specify the precise weld size, there is an industry-standard fallback value that you must always use.

The minimum fillet weld size is about 3mm. If you calculate your fillet weld size to be lower than this value, there’s either a problem with your calculation or with your entire weld. It’s important to recalculate to avoid errors in your fillet weld.

Since the thickness of the metal you’ll be welding will vary wildly, there is no definite maximum fillet weld size for all applications. However, the maximum size is taken to be 0.7t, where “t” represents the thickness of the base metal for the fillet legs.

As you may already know, you should always default to the smallest value if both of your fillet legs don’t have the same base metal thickness. You may never have to do that, however, as it’s a pretty rare phenomenon.

How to Calculate Weld Size

If you already know the plate thickness of your weld, you can easily find the leg size, which is the same thing as the weld size in fillet welds. Note that in cases where there are two different plate thicknesses, the thickness for the thinner leg will be applicable this instance.

With that said, the value of the leg size in any given fillet weld should be equal to three fourth the value of the plate thickness. If you’re making the weld on only one leg of the weld, you should double the value from your calculation.

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