AWS A2.4:2020 · Step-by-Step Guide

How to Read Symboles de Soudage — Step-by-Step

A Symbole de soudage is read in a fixed sequence: (1) find the Ligne de référence, (2) identify Côté flèche vs. Autre côté, (3) read the Type de soudure symbol, (4) read Taille and length dimensions, (5) check for finishing codes or tail notes. Per AWS A2.4:2020.

Every Soudage symbol per AWS A2.4 has the same anatomy: a horizontal reference line, an arrow pointing to the joint, a weld type symbol (triangle for fillet, V for groove), dimension numbers, and optional elements in the tail. Arrow-side welds go below the reference line; other-side welds go above. Reading symbols is the first skill every Inspecteur en soudage learns.

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Reading Sequence

The 5-Step Reading Method

STEP 01

Find the Reference Line

The reference line is always a horizontal line. Find it first. Everything else attaches to it — the arrow connects below or to one end; dimensions and weld symbols sit above or below it. The reference line is the anchor. Once you have it, the rest follows.

STEP 02

Identify Arrow Side vs. Other Side

The arrow points from the reference line to the actual joint on the drawing. The arrow side of the joint is where the arrow points. Any Symbole de soudure placed below the reference line applies to the arrow side. Any symbol placed above the reference line applies to the other side — the opposite face of the joint. Both sides shown = weld both sides.

STEP 03

Identify the Weld Type

The weld symbol graphic tells you the weld type per AWS A2.4:2020:

Right triangle (perpendicular leg on left) = Soudure d'Angle — the most common weld in Acier de construction.

Open-V = V-Soudure sur chanfrein. Open-V with one straight side = Chanfrein en demi-V. Square groove = two parallel lines from the reference line.

Circle on reference line = plug or Soudure en entaille (filled circle = plug; elongated shape = slot).

Two half-circles = Soudure en continu. No symbol with broken arrow = bevel or Chanfrein en J on the arrow member.

STEP 04

Read the Dimensions

Left of the weld symbol = Dimension de soudure. For fillet welds, this is the leg length. For groove welds, the groove depth D appears without parentheses, and the weld size (S) appears in parentheses — written as D(S) per A2.4 §7.2.6.

Right of the weld symbol = length and pitch for intermittent welds. Written as length-pitch: 3-12 means 3-inch welds placed 12 inches center-to-center. No number to the right = the weld is continuous.

No size on a groove weld = CJP (complete joint penetration). The joint must be fully fused through its entire Épaisseur.

STEP 05

Check for Special Indicators

Solid triangle flag at junction = Soudure sur chantier. The weld must be made at the erection site, not in the shop.

Circle at junction = Soudure tout autour. The weld must be made continuously around the full joint perimeter.

Tail (V-shape at the reference line end opposite the arrow) = WPS reference number, process designation (SMAW, FCAW, GMAW), or special instruction. No tail = no special note required.

Contour and finish symbols = a letter on or near the weld symbol (C = chipping, G = grinding, M = machining, U = unspecified) with a straight or Convexe/Concave contour line indicates a finishing requirement after welding.

Worked Example

Reading a Real Fillet Weld Symbol

Take a welding symbol showing: a right triangle below the reference line with the number 3/8 to its left and 3-12 to its right. Here is the full reading:

Symbol Reading

Step 1 — Reference line: Found. Horizontal line with arrow and triangle.

Step 2 — Arrow side: Triangle is below the reference line = arrow side weld.

Step 3 — Weld type: Right triangle with perpendicular leg on left = fillet weld.

Step 4 — Dimensions: 3/8 to the left = 3/8-inch fillet leg size. 3-12 to the right = 3-inch weld segments, 12-inch center-to-center pitch (intermittent fillet weld).

Step 5 — Special indicators: No flag, no circle, no tail. Norme shop weld, no special finishing required.

Full reading: Make 3/8-inch fillet welds on the arrow side of the joint. Each weld segment is 3 inches long, spaced 12 inches center-to-center along the joint.

Inspector check: When inspecting this weld, measure the actual fillet leg with a fillet weld gauge — Vérifier each segment is 3 inches long and that the spacing does not exceed 12 inches center-to-center. Per D1.1, intermittent fillet length is measured to the nearest 1/4 inch.

Common Questions

How to Read Weld Symbols FAQ

How do you read a welding symbol step by step?

Read a welding symbol in five steps per AWS A2.4:2020. Step 1: find the horizontal reference line — everything else attaches to it. Step 2: identify which side of the joint is the arrow side (where the arrow points) and which is the other side. Step 3: read the weld type symbol — a right triangle below the line means a fillet weld on the arrow side; an open-V means a V-groove. Step 4: read the dimensions — the number to the left is the weld size; numbers to the right are length and pitch for intermittent welds. Step 5: check for special indicators such as a field weld flag (solid triangle at the junction), a weld-all-around circle, or tail notes referencing a WPS number.

What does the number to the left of a weld symbol mean?

The number to the left of a weld symbol is the weld size. For a fillet weld, it is the leg length — for example, 5/16 means a 5/16-inch (8mm) leg. For groove welds, the groove depth D appears without parentheses and the weld size (S) appears in parentheses, written as D(S) per A2.4 section 7.2.6. If the size appears on the same side as the weld symbol (below for arrow side, above for other side), it applies to that side only. A CJP groove weld has no size dimension — the weld fills the full joint.

What does a circle on a welding symbol mean?

A small circle at the junction of the reference line and the arrow is the weld-all-around symbol per AWS A2.4:2020. It means the weld must be made completely around the joint perimeter — for example, all four sides of a tube-to-plate connection or the full circumference of a pipe sleeve penetration. The circle is placed at the reference line / arrow junction, not on the weld symbol itself. Do not confuse it with the field weld flag, which is a solid filled triangle at the same junction.

What does a flag on a welding symbol mean?

A solid triangular flag at the junction of the reference line and arrow is the field weld symbol per AWS A2.4:2020. It means the weld must be made in the field — at the erection or installation site — not in the fabrication shop. Field welds are significant because they affect inspection scheduling, preheat requirements (field conditions differ from shop conditions), and logistics. Per A2.4 §6.9, the flag may point in either direction. It can appear alongside a weld-all-around circle when the weld is both field-made and continuous around the joint.

Related Reference

More Symbol Resources

"Reading weld symbols is the first skill every welding Inspecteur learns — and the one they use every single day. If you cannot read the symbol, you cannot inspect the joint. I tell every CWI candidate: master A2.4 before you open D1.1."
— Field observation, CWI practice

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