Simple Guide: How to Read Welding Symbols (AWS A2.4 Explained)

Simple Guide: How to Read Welding Symbols (AWS A2.4 Explained)

1. Introduction

In fabrication drawings, welding symbols are the hidden language between engineers and welders.
They convey how two pieces of metal should be joined — from the type of weld and size,
to the location, finish, and process.
If you can read them fluently, you can turn complex blueprints into precise, safe welds.

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2. Understanding the Welding Symbol Structure

A welding symbol consists of three main parts:

• Reference line: The foundation line where all information is attached.
• Arrow: Points to the joint to be welded.
• Tail: Used for process or reference notes (optional).

Basic structure of a welding symbol used in engineering drawings. Location: Below this section.

 

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3. Common Weld Types & Symbols

Each weld type has its own unique symbol:

• Fillet weld: A right-angled triangle – the most common joint type.
• Groove weld: Used when metal edges are prepared for deep penetration.
• Plug/Slot weld: Circular or slotted holes filled with weld metal.
• Spot weld: Circular mark – common in sheet metal works.

Image suggestion:
File name: common-weld-symbols-chart.jpg

Common weld types and their standard symbols (AWS A2.4).

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4. Arrow Side vs Other Side

The arrow side indicates where the weld is applied relative to the reference line.
If the symbol appears below the line, weld the arrow side.
If it appears above, weld the opposite side.
This distinction is crucial in multi-pass or double-sided joints.

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5. Supplementary & Finishing Symbols

Welding symbols often include:

• Contour symbols (flat, convex, concave)
• Finish methods (grinding, machining, etc.)
• Weld all around circle
• Field weld flag

Image suggestion:
File name: weld-finish-symbols-chart.jpg

Supplementary symbols that define weld contour and field work conditions.

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6. Reading Example

Let’s interpret an example:

A fillet weld symbol below the reference line with “6” on the left and “100” on the right
means a 6 mm fillet weld, 100 mm long, on the arrow side.
Once you understand this pattern, complex blueprints become readable at a glance.

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7. Summary

Learning welding symbols isn’t just about memorizing icons — it’s about visualizing how a joint will look once welded.
For engineers, it ensures clear communication; for welders, it ensures precision and safety.

 

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