What is the minimum diameter for a hole or slot fillet weld?

What is the minimum diameter for a hole or slot fillet weld?

• A. No less than the thickness of the material
• B. Twice the thickness
• C. Thickness plus 12 mm
• D. Thickness plus 8 mm (5/16")

Answer: (D)

When you weld through a hole or slot (a plug or through-hole fillet weld), the weld must surround the edge of the opening enough to carry the load in the joint. That means the opening can’t be just as big as the plate thickness; there must be extra weld metal around the circumference to establish a proper fillet and throat for the load transfer. The standard requirement used in practice is to make the hole or slot diameter at least the plate thickness plus an added amount of 8 mm (which is 5/16 inch). This added allowance ensures there is enough weld around the opening to achieve the necessary throat and leg length, giving adequate strength for the joint. Choosing a diameter equal to the thickness would yield too little weld around the opening; choosing twice the thickness or thickness plus a larger amount would exceed the standard minimum and isn’t required for this rule. Therefore, the minimum diameter is thickness plus 8 mm (5/16").

When you weld through a hole or slot (a plug or through-hole fillet weld), the weld must surround the edge of the opening enough to carry the load in the joint. That means the opening can’t be just as big as the plate thickness; there must be extra weld metal around the circumference to establish a proper fillet and throat for the load transfer.

The standard requirement used in practice is to make the hole or slot diameter at least the plate thickness plus an added amount of 8 mm (which is 5/16 inch). This added allowance ensures there is enough weld around the opening to achieve the necessary throat and leg length, giving adequate strength for the joint.

Choosing a diameter equal to the thickness would yield too little weld around the opening; choosing twice the thickness or thickness plus a larger amount would exceed the standard minimum and isn’t required for this rule. Therefore, the minimum diameter is thickness plus 8 mm (5/16").