Fillet Weld Symbols
Vocabulary
Fillet welds are among the most common welds used in fabrication and structural welding. They are used to join two pieces of metal at right angles in T-joints, lap joints, and corner joints. The fillet weld symbol is essential for understanding how to prepare and weld these joints correctly.
A fillet weld symbol looks like a small right triangle placed on the reference line of the welding symbol. The vertical leg represents the weld leg, the horizontal leg represents the adjoining surface, and the slanted side represents the weld face.
Arrow Side vs. Other Side: If the fillet weld symbol appears below the reference line, weld the arrow side. If the symbol is above the reference line, weld the other side. If symbols appear on both sides, weld both sides.
Fillet Weld Size: The weld size is written to the left of the fillet weld symbol and refers to the leg size of the weld. For example, ‘1/4 ⧍’ means a 1/4-inch fillet weld. If the weld is required on both sides, the size applies to each side unless stated otherwise.
Length of Fillet Weld: If the weld is not continuous, the length appears to the right of the symbol. For example, ‘1/4 ⧍ 2’ means a 1/4-inch fillet weld that is 2 inches long. For intermittent welds, pitch and segment length may also be included.
Intermittent Fillet Welds: These are welds applied in spaced segments. Chain intermittent welds have segments directly across from each other, while staggered intermittent welds have alternating segments on each side. These patterns reduce heat distortion while maintaining strength.
Contour Symbols: Fillet welds may require a specific finished shape—flat, convex, or concave. These contours are shown with a straight line, outward curve, or inward curve respectively. If a finishing method is needed, the symbol may include letters such as ‘G’ for grinding or ‘M’ for machining.
All-Around Symbol: A small circle at the elbow of the welding symbol means to weld all the way around the joint. This is common on posts, frames, and pipe-to-plate connections.
Field Weld Symbol: A small flag indicates that the weld must be made in the field rather than in the shop. Field welds often require different preparation and safety considerations.
Common Uses: Fillet welds appear in T-joints, lap joints, corner joints, brackets, frames, structural members, and machine bases. They are valued for their strength, versatility, and faster setup compared to groove welds.
Understanding fillet weld symbols helps welders prepare joints correctly, apply welds to the correct side, achieve the required weld size, and meet engineering standards. Incorrect interpretation can lead to failed welds, rework, or structural issues.
