Drawing Reading, Welding Symbols and Code Requirements
Symbol anatomy
The AWS A2.4 symbol has a reference line, an arrow, a tail and the weld symbol placed above (other side) or below (arrow side) the line. For a fillet, the leg size goes to the left of the symbol, and the length and pitch to the right. For a groove weld the symbol shape shows the type, with the groove angle, root opening and root face written adjacent. A circle at the elbow means weld all around; a flag means field weld; the tail carries the process, specification or code reference. Contour symbols (flush, convex, concave) sit above the weld symbol with the finishing method.
Reading order
- Identify the joint and which side the arrow points to.
- Identify the weld type from the symbol.
- Read size, then length and pitch.
- Read supplementary dimensions: groove angle, root opening, root face.
- Read tail notes, all-around and field-weld flags.
Code framework
AWS D1.1 governs structural steel, ASME Section IX governs procedure and performance qualification, API 1104 covers pipelines, ASME B31.3 covers process piping. The symbol says where and how much; the WPS says how.
Worked example
Arrow-side fillet marked 6-75/150, all-around circle, field-weld flag, tail "AWS D1.1". Read: 6 mm fillet leg, 75 mm long weld segments on a 150 mm pitch (centre to centre), applied continuously around the entire joint, welded in the field to AWS D1.1. Length and pitch describe intermittent welding; they are not a single 75 mm weld placed 150 mm from the corner.
Traps
- Placing the size to the right of the symbol instead of the left.
- Confusing all-around (circle) with both-sides welding, which uses two fillet triangles, one each side of the reference line.
- Ignoring tail notes, which often carry the governing code or process.