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Fillet Weld for Socket Fittings

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A fillet weld is defined, by the American Welding Society (AWS), as “A weld of approximately triangular cross section joining two surfaces approximately at right angles to each other in a lap joint, T-joint, or corner joint.” This type of welding technique is used to connect socket weld fittings or slip on flanges to pipes.


The three common types (lap joint, tee joint, corner joint) are shown in the image:
Fillet Weld types
Fillet Weld types


This type of welded connection is made by the legs, the toes, the face, the throat, and the root as shown in the image below. The throat, which is used to calculate its strength, can be defined as the distance between the root and face of the weld.
The anatomy of a fillet weld
Fillet Welds Anatomy

The basic fillet weld symbol consists of a reference line, an arrow line, the tail, Weld Procedure Specification (WPS) information, and the fillet weld symbol including leg size. The most common elements of this type of welds are shown in the picture below.

The reference line is always drawn horizontally, it contains the weld type information and connects the arrow line and the tail. The arrow line points to the weld location.

The underside of the reference line is referred to as the arrow side, weld symbols drawing on this side of the reference line are placed to the arrow side of the components; weld symbols located above the reference line are placed on the components to the side opposite the arrow.

The tail is actually an optional element and contains information regarding the weld. The WPS identifies the procedures and parameters that the welder uses to execute the weld. Notes and other information on the weld can be included in the tail.

The fillet weld symbol is represented as a triangle. The leg size of the fillet weld is placed to the left of the fillet symbol.

Most, but not all fillet welds are of equal legs. When the legs are not equal the leg sizes are indicated for example by 1 x 1.25.

At the juncture of the reference line and tail, a circle indicates the welding go entirely around the feature the arrow line is pointing at. Commonly applied to circular features, this instruction is not limited to them.

A darkened flag at the juncture of the reference line and tail indicates the weld is to be performed in the field.


WPS of fillet welds

Fillet welds do not have to be continuous, the length and pitch between centers of an intermittent fillet weld are shown to the right of the welding symbol. Fillets welds are not necessarily limited to one side of the components to be joined.

Fillets welds can be made on both the arrow side and opposite side of the components. These welds could be continuous or intermittent.

The face of a fillet weld can be required to be flat, convex, or concave. If the face requires finish processing it could be chipped (C), ground (G), hammered (H), machined (M), rolled (R), or peened (P) as shown in the picture:

Contour of fillet welds

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