△ Welding symbol
Welding symbol · Soldadura en plano · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Triangle both sides + a 6 mm + ISO 5817” states a welding symbol requirement.
What controls
A composite annotation that brings together in one place everything that defines a weld: an arrow pointing at the joint, a horizontal reference line, the basic symbol for the type of weld, the dimensions (throat or leg, length, pitch) and a tail carrying the process, the quality level or the applicable procedure. The position of the symbol relative to the reference line says which side of the joint the weld goes on; if a symbol appears above and below, there is a weld on both sides. What the symbol does NOT define is how to weld: amperage, number of passes, filler metal and preheat come from the welding procedure specification (WPS), not from the drawing.
How to verify
Size is verified with weld gauges (leg or throat gauge) placed on the weld after cleaning off slag and spatter; length and pitch with a tape measure. The joint type and side are checked visually against the drawing before the part moves on to the next station. Whatever the tail requires (for example a quality level or a non-destructive test) is closed out with the corresponding report, not with the gauge.
Common mistakes when interpreting it
- Reading the symbol above the reference line as if it were the arrow side: they are opposite sides of the joint and the weld ends up where it does not belong.
- Ignoring the tail of the symbol and welding “the usual way”: that is usually where the process and acceptance level the inspector will later require are stated.
- Taking the weld dimension as its length: the number to the left of the symbol is the throat or leg size, not how long the weld is.
How to get it in the workshop / if it comes out of tolerance
Read the symbol in this order: which joint the arrow points to, what type of weld it is, which side it goes on, what size it is and what the tail says. The dimension to the left of the symbol is the weld size and the one to the right its length and pitch; mixing them up is the most expensive mistake in a welding shop. Everything in the tail (process, acceptance level, procedure) is as mandatory as the size.
If the weld comes out undersize, the usual cause is high travel speed or insufficient deposition: reduce travel speed or add passes before touching the current. If it comes out oversize, besides wasting filler it puts in more heat and more distortion. A weld placed on the wrong side of the joint is not fixed by welding the other side as well: engineering must assess whether it is removed or accepted by documented deviation.
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