Welding Symbols on Engineering Drawings: How to Read Them Under AWS and ISO

That is why a quick shop chart is useful for recognition, but it should not replace the standard or project notes. Some welding symbol charts explicitly state that they are shop aids only and that the complete official presentation of AWS symbols is in AWS A2.4 .

2. Know the difference between a weld symbol and a welding symbol

Two terms are easy to mix up:

• Weld symbol: the small pictorial mark that identifies the type of weld, such as a fillet weld or groove weld.
• Welding symbol: the complete instruction system, including the arrow, reference line, tail, dimensions and supplementary symbols when used.

Educational welding references make this distinction clearly: the weld symbol is the shape that identifies the type of weld, while the welding symbol is the full set of information carried by the reference line, arrow and tail . In practice, recognising a triangle as a fillet weld is only the beginning. You still need to know which side of the joint it applies to, how large it is, how long it is, and whether a procedure or specification is referenced.

3. Identify the main parts of the welding symbol

4. Work out the weld side: arrow side or other side?

In common AWS-style reading, the position of the weld symbol relative to the reference line tells you which side of the joint is to be welded:

• Below the reference line means the weld is on the arrow side .
• Above the reference line means the weld is on the other side of the joint .
• Symbols or information on both sides of the reference line can mean welding is required on both sides .

Do not automatically apply that rule to every drawing. In BS EN 22553-style references, weld symbols on the full reference line relate to the near side of the plate, while symbols on the dashed line relate to the far side; if welds are symmetrical on both sides, the dashed line can be omitted . This is the reason the drawing standard comes before symbol interpretation.

5. Read the basic weld type

Fillet weld

A fillet weld is commonly shown by a triangular symbol and is used where parts meet at an angle or intersection. Once you know whether the triangle is above or below the reference line, read the nearby numbers because they may define the weld size or length .

Groove welds and butt joints

A groove weld symbol indicates that one or both edges of the joint are prepared and the groove is then filled with weld metal. Symbol charts include square groove, V-groove, bevel groove, U-groove, J-groove, flare-V and flare-bevel forms . A groove weld symbol may also include size, depth of preparation, root opening, groove angle, contour, finishing method, length and pitch .

Plug welds and slot welds

Plug and slot welds appear among the basic weld symbols in welding symbol charts . When you see them, pay close attention to pitch or spacing. One welding guide notes that plug weld pitch appears to the right of the rectangle, while slot weld spacing information can appear next to the symbol .

Spot, seam, surfacing, edge and backing symbols

Welding symbol charts also include spot welds, seam welds, surfacing, edge welds, and back or backing symbols . For these, the symbol name alone is not enough. Read the arrow, dimensions and tail because the actual execution may be controlled by a specification, process or other referenced procedure .

6. Decode the numbers around the symbol

The numbers turn the symbol from a general idea into a buildable instruction. AWS-style element diagrams provide locations for weld size, depth of bevel, groove angle, root opening, weld segment length and pitch or centre-to-centre spacing .

A practical reading order is:

1. Size: Start with the number closest to the weld symbol, especially for fillet and groove welds .
2. Length: If the weld is not continuous, a weld segment length may appear next to the symbol .
3. Pitch: This gives centre-to-centre spacing between weld segments or openings, depending on the weld type .
4. Root opening and groove angle: These commonly appear with groove welds because they define joint preparation before welding .
5. Contour and finish: Symbols may specify a flat, convex or concave contour, and a finishing method may be added when required .

Supplementary symbols worth checking every time

• Weld all around: Shown as a circle where the arrow line meets the reference line; it means the weld is required all the way around the joint as defined by the drawing .
• Field weld: Commonly shown as a small flag at the reference line; it indicates a weld made in the field or at the installation site rather than in the fabrication shop .
• Weld contour: Flat, convex and concave contour symbols define the required final surface form of the weld .
• Tail information: The tail may include a welding process, specification or other reference, and may be left off when no added reference is needed .

Quick reading examples

A triangle below the reference line on an AWS-style drawing
Follow the arrow to the joint first. Because the weld symbol is below the reference line, the weld is on the arrow side. Because the triangle is a fillet weld symbol, the callout is for a fillet weld on that side, with any nearby number defining size or length as applicable .

A V-groove symbol with an angle and root opening
This indicates a groove weld with V-shaped preparation. The V alone is not the full instruction; the groove angle, root opening and preparation depth are part of the weld requirement and must be read with the symbol .

A small circle at the arrow and reference-line junction
This is the weld-all-around symbol. It tells you the weld is not limited to one visible edge in the view, but continues around the joint according to the drawing .

A small flag at the reference line
This is the field weld symbol. It separates a weld to be made at the installation or assembly site from one made in the fabrication shop .

Six-step checklist for reading welding symbols

1. Read the standard in the title block or notes: AWS A2.4, ISO 2553, BS EN 22553, or a project-specific reference .
2. Follow the arrow to the joint. The arrow connects the reference line to the location where the welding instruction applies .
3. Determine the side using the weld symbol’s position relative to the reference line, or the full-line and dashed-line system if that is the convention on the drawing .
4. Identify the weld type from the basic symbol: fillet, groove, plug, slot, spot, seam, surfacing, edge or another listed type .
5. Read the dimensions: size, length, pitch, root opening, groove angle and depth of preparation as applicable .
6. Check the tail and notes for process, specification, procedure reference or inspection details not shown directly in the symbol .

Common mistakes to avoid

• Reading only the shape: A triangle or V is not enough. The full welding symbol includes the reference line, arrow, tail and dimensions when present .
• Mixing up arrow side and other side: In common AWS-style reading, a weld symbol below the reference line does not mean the same thing as one above it .
• Ignoring different systems: A dashed line in BS EN 22553-style references changes how the near and far sides are identified .
• Skipping the numbers: Size, length, pitch, root opening and groove angle can be essential parts of the required weld .
• Relying only on a pocket chart: Charts are helpful reminders, but they are not a substitute for the official standard or the project drawing notes .

Bottom line

Read a welding symbol as a complete technical sentence. The standard tells you the grammar, the arrow points to the joint, the reference line organises the instruction, the weld symbol names the weld type, and the dimensions and supplementary symbols control how the weld is made. Read in that order, the small marks on a drawing become clear instructions for weld location, type, size and execution requirements .