How to Read and Apply Weld Symbols on Technical Drawings

In the world of manufacturing, weld symbols are essential for communicating how parts should be joined. Whether you're working in sheet metal fabrication, structural steelwork, or CNC machining services, understanding symbols in welding ensures accuracy, efficiency, and safety. This guide breaks down welding symbols on drawings so you can read and apply them confidently, following both UK welding symbols and international standards.

What Are Weld Symbols?

Weld symbols are graphical representations used in technical drawings to indicate the type, size, and placement of welds. They serve as a universal language for engineers, designers, and welders. A weld symbol chart helps standardize this communication. These symbols are vital across industries, including sheet metal welding and heavy fabrication.

Here’s a visual example of welding symbols on drawings showing the relationship between components like reference lines, arrows, and tails.

Common Components of Weld Symbols

Each welding symbol consists of several important components that convey precise welding instructions. Here’s a breakdown of these essential parts.

Reference line

The reference line is the foundation of the weld symbol. It serves as the baseline on which other parts of the symbol are placed. All information about the weld—type, size, and additional instructions-is anchored to this line.

Arrow

The arrow points to the joint that needs welding. Understanding "arrow side" versus "other side" is crucial in interpreting symbols in welding, especially in UK welding symbols, where this distinction affects how the weld is performed.

Weld symbol body

The body of the symbol tells you what kind of weld is required, such as fillet, groove, plug, or slot. Every weld symbol chart includes these basics, making it a vital reference for interpreting welding symbols on drawings.

Weld size

The weld size is indicated to the left of the symbol and specifies dimensions critical to strength and function. This detail is essential when working on sheet metal welding, where precision matters.

Tail

The tail may include additional details like the welding method (e.g., TIG, MIG), filler materials, or inspection requirements. Though not always used, it can contain vital information in welding symbols on drawings.

Finishing and processing symbols

These symbols specify post-weld operations like grinding or machining, ensuring the final product meets design and aesthetic requirements - particularly relevant in sheet metal fabrication.

How to Interpret Weld Symbols

Interpreting weld symbols requires analyzing each element in sequence. Start with the arrow to identify the weld location, move to the weld symbol body for type, check the weld size, and read the tail for any special instructions.

For example, a UK welding symbol showing a fillet weld with a "6" next to it and "TIG" in the tail means applying a 6mm fillet weld using TIG welding on the arrow side. Systematically reading welding symbols on drawings prevents costly errors and improves build quality.

Types of Weld Symbols and Their Application

Different types of welding symbols represent various welding techniques used in fabricating parts and assemblies.

Basic welding symbols

Here are some essential weld symbols and their uses:

Supplementary symbols

Supplementary symbols refine the instructions, indicating finishes or special treatments:

UK-Specific Weld Symbols and Standards

In the United Kingdom, weld symbols UK are typically governed by BS EN ISO 2553, which aligns with the ISO standard for welding symbols. However, there are specific nuances in how these welding symbols are applied compared to other regions, such as the United States.

When working with welding symbols, it's critical to ensure alignment with ISO standards, especially in international projects where differences could impact the final product.  

Learn more about sheet metal welding and sheet metal materials to apply these symbols in practical fabrication settings.

Variations in Weld Symbols Across Countries

Different standards govern symbols in welding globally. In the UK, BS EN ISO 2553 applies, while the US uses AWS A2.4.

Typical Mistakes in Reading Weld Symbols

Even experienced engineers and fabricators can make mistakes when interpreting weld symbols, especially when working under tight deadlines or with unfamiliar standards. Misreading welding symbols on drawings can lead to severe consequences, including structural failures, costly rework, and production delays. Below are some of the most common mistakes and how to avoid them:

1. Confusing arrow side vs. other side
   One of the most frequent errors in reading weld symbols and ISO standard for welding symbols is misunderstanding which side of the joint should be welded. In UK welding symbols, a solid reference line indicates the arrow side, and a dashed reference line refers to the opposite side. Mistaking these can result in welds placed on the wrong side of the joint, weakening the final assembly. Always double-check which side the symbol is referencing before welding begins.
2. Ignoring or misinterpreting weld size and length
   The size and length of the weld, typically noted to the left and right of the weld symbol body, are critical for structural integrity. Overlooking these can cause under-welding or over-welding, both of which can compromise the part’s function and lead to failures. Always ensure that weld sizes match the specified values, particularly in sheet metal welding, where precision is key.
3. Overlooking supplementary and finishing symbols
   Supplementary symbols like convex, concave, flush, and contouring often provide essential finishing instructions. Missing these details may affect both the strength and appearance of the final product. For example, a weld specified to be ground flush but left unfinished could interfere with part fitment or performance.
4. Neglecting process specifications in the tail
   The tail of a weld symbol often includes important instructions, such as required welding processes (e.g., TIG, MIG, Stick) or filler materials. Ignoring these can lead to inappropriate weld methods being used, affecting weld quality and compliance with standards.
5. Mixing up different international systems
   Engineers working on multinational projects may confuse UK weld symbols with AWS or other international systems. Since symbols in welding vary across standards, always verify which system is being used and ensure everyone on the team is aligned.

How to Apply Weld Symbols on Technical Drawings

Applying weld symbols on technical drawings is a vital skill for engineers and designers to ensure that their specifications are clearly communicated to the fabrication team. When done correctly, symbols in welding remove ambiguity and prevent costly errors during production. Here’s a step-by-step process for applying weld symbols UK standards to your drawings:

1. Understand the joint type

Start by identifying what type of joint you are designing - lap joint, butt joint, corner joint, etc. Each joint type may require a specific kind of weld (e.g., fillet, groove). Knowing the joint type will guide the selection of the appropriate weld symbol body.

2. Select the appropriate weld symbol

Using a weld symbol chart, choose the correct symbol for the type of weld you want. For example:

• A triangle symbol for a fillet weld.
• A V symbol for a groove weld.
• A circle symbol for a plug weld.

Ensure that the symbol is standardized according to UK weld symbols or ISO standard for welding symbols, depending on project requirements.

3. Specify the weld location with reference line and arrow

Attach the symbol to a reference line, and draw an arrow pointing to the joint. Decide if the weld will be on the arrow side (solid line) or other side (dashed line). If welding on both sides is needed, use symbols placed on both sides of the reference line.

4. Add weld size, length, and spacing

Indicate the required weld size to the left of the symbol and length or pitch (spacing) to the right. For example, "6" means a 6mm fillet weld. This is essential for ensuring that the weld meets strength and design specifications.

5. Include additional information in the tail

If specific processes, filler metals, or finishing instructions are required, note them in the tail of the weld symbol. For instance, adding "TIG" ensures the welder uses the correct process.

6. Consider supplementary and finishing symbols

If your weld requires a special contour or post-weld finish, add the appropriate supplementary symbol (e.g., convex, concave, flush) above or below the reference line, depending on weld orientation.

7. Review and validate

Once applied, review the entire drawing to ensure all weld symbols are accurate, clear, and consistent. At Geomiq, our engineering team often reviews client drawings to check for completeness and accuracy before production.

Importance of Consistency in Weld Symbols

Using consistent welding symbols on drawings ensures that designers, engineers, and fabricators understand the requirements without confusion. At Geomiq, we emphasize precision and clarity when working with sheet metal materials and welded assemblies to prevent costly mistakes.

How Geomiq Can Help You

If you need support with interpreting or applying welding symbols on drawings, Geomiq is here to help. Our team of experienced engineers can review and optimize your technical drawings, ensuring that every weld symbol is clear, consistent, and aligned with manufacturing standards. 

We provide sheet metal fabrication, injection molding, CNC machining services, and more, ensuring your parts are produced with precision.