How to read a weld symbol

A weld symbol is about an inch of ink on a drawing and it contains the entire instruction: what kind of weld, how big, which side, how long, how far apart, and by what process. Get one of those wrong and you have spent two hours welding something that has to be ground off.

The good news is that there are only about eight positions on a welding symbol and every one of them is fixed by AWS A2.4. Position carries the meaning. Once you know where to look, you are not interpreting anything. You are reading.

The anatomy

Here is one symbol with everything on it, which almost never happens in real life but shows you where each piece lives.

Working through it, in the order the numbers are marked:

1. The arrow points at the joint. Not at a general area. At the specific joint being welded.
2. The reference line is the horizontal line. It is the spine of the whole symbol.
3. The weld symbol is the shape sitting on the line. A triangle is a fillet. A square is a square groove. A V is a V groove, and so on.
4. Size sits to the left of the weld symbol. On a fillet, that is your leg length.
5. Length and pitch sit to the right. Two inch welds on six inch centres in the example above.
6. The tail carries the process, the specification, or a note. If there is nothing to say, there is no tail.
7. The circle at the elbow means weld all around.
8. The flag means field weld, done at the site rather than in the shop.

The one that catches people out

Which side gets welded is decided by whether the weld symbol sits below the reference line or above it. This is the single most common thing to get backwards, and it costs the most to fix.

Below the line is arrow side. Above the line is other side. Symbols on both sides means weld both sides, and the sizes can be different.

The memory hook that sticks for most people: the symbol below the line is closer to the arrow, and the arrow is touching the side you weld.

Intermittent welds, and the mistake that eats material

When you see something like 1/4 2-6 on a fillet, that is a quarter inch leg, two inch long welds, on six inch pitch.

Pitch is measured centre to centre, not gap to gap. So on a six inch pitch with two inch welds you have four inches of gap between them, not six. People who measure the gap instead of the centres end up with a third more weld than the print asked for, which sounds harmless until you are looking at distortion on a long member.

If the symbols on both sides of the line are offset from each other, that is a staggered intermittent weld. Lined up, that is chain intermittent. It matters, because staggered is usually specified to control exactly the distortion you would cause by chaining it.

How to actually get fluent

Reading about symbols does not make you fluent. Two things do.

First, take any drawing you have access to and translate every callout on it into a full English sentence out loud. Not shorthand. The whole thing: quarter inch fillet, arrow side, two inch welds on six inch centres, GMAW, all around. Do that for thirty callouts and it stops being a lookup.

Second, learn the ones your industry actually uses. Structural work runs on fillets and a handful of groove symbols. Pipe runs on a different small set. Nobody has all of AWS A2.4 in their head and nobody needs it. You need the twelve you see every week, cold.

Short version

• Position on the symbol carries the meaning. Every piece has a fixed home.
• Below the reference line is arrow side. Above it is the other side.
• Size on the left, length and pitch on the right, process in the tail.
• Pitch is centre to centre.
• Circle at the elbow is all around. Flag is field weld.
• Read thirty real callouts out loud in full sentences and you will stop looking them up.

Next: TIG or MIG, which to learn first.