Welding Symbols Explained

III. Types of Welding Symbols

Welding symbols are essential tools in the fabrication industry, providing standardized instructions for creating specific welds. Understanding these symbols is crucial for welders, engineers, and inspectors to ensure that welds meet design and safety standards. In this section, we will explore various types of welding symbols, their meanings, and their applications.

Basic Weld Symbols

Basic weld symbols indicate the type of weld to be made and are the foundation of welding instructions on drawings. The most common basic weld symbols include:

1. Fillet Weld Symbol
2. Groove Weld Symbol
3. Plug and Slot Weld Symbols
4. Spot and Projection Weld Symbols
5. Seam Weld Symbol
6. Back and Backing Weld Symbols
7. Surfacing Weld Symbol
8. Edge Weld Symbol
9. Butt Weld Symbol
10. Socket Weld Symbol

Fillet Weld Symbol

The fillet weld symbol represents a weld of triangular cross-section that joins two surfaces at approximately right angles to each other. It is one of the most commonly used welding symbols.

Characteristics:

• Shape: Triangular cross-section.
• Applications: T-joints, lap joints, and corner joints.
• Symbol Representation: A right-angle triangle on the reference line.

Groove Weld Symbol

Groove welds are used to join two members in a butt joint, corner joint, or T-joint. There are several types of groove welds, each represented by a specific symbol.

Types of Groove Welds:

• Square Groove: Straight line symbol.
• V-Groove: V-shaped symbol.
• Bevel Groove: Single bevel shape.
• U-Groove: U-shaped symbol.
• J-Groove: J-shaped symbol.
• Flare-V Groove: Flared V shape.
• Flare Bevel Groove: Flared bevel shape.

Plug and Slot Weld Symbols

Plug and slot welds are used to join two overlapping pieces of metal. The weld fills a hole (plug) or a slot in one of the pieces.

Characteristics:

• Plug Weld Symbol: Circle on the reference line.
• Slot Weld Symbol: Rectangle on the reference line.

Spot and Projection Weld Symbols

Spot and projection welds are used to join overlapping pieces of metal at small, localized points.

Characteristics:

• Spot Weld Symbol: Small circle.
• Projection Weld Symbol: Projection symbol or notation.

Seam Weld Symbol

Seam welds are continuous welds made along the length of a joint. They are often used in manufacturing pipes and tubes.

Characteristics:

• Symbol: A line with a series of evenly spaced dots.

Back and Backing Weld Symbols

Back and backing welds are used to add reinforcement to the root of a weld. These symbols indicate that a weld is to be made on the backside of the joint.

Characteristics:

• Back Weld Symbol: Line with a symbol for back weld.
• Backing Weld Symbol: Line with a symbol for backing.

Surfacing Weld Symbol

Surfacing welds are used to apply a layer of weld metal to the surface of a workpiece for purposes such as wear resistance or corrosion protection.

Characteristics:

• Symbol: A line with a surfacing notation.

Edge Weld Symbol

Edge welds are used to join the edges of two or more pieces of metal. This type of weld is often used when the edges of the materials need to be sealed or reinforced.

Characteristics:

• Symbol: Line with an edge weld symbol.

Supplementary Weld Symbols

Supplementary weld symbols provide additional information about the weld, such as the desired contour, finish, or additional instructions. Common supplementary symbols include:

1. Contour Symbols
2. Finish Symbols
3. Weld All Around Symbol
4. Field Weld Symbol
5. Melt-Through Symbol

Contour Symbols

Contour symbols indicate the desired shape or contour of the finished weld. They are often used in combination with finish symbols.

Types:

• Flush Contour: Flat line.
• Convex Contour: Curved outward line.
• Concave Contour: Curved inward line.

Finish Symbols

Finish symbols provide instructions on how the weld should be finished, such as grinding, machining, or other finishing processes.

Types:

• Grind: Indicated by the letter “G”.
• Machine: Indicated by the letter “C”.
• Chip: Indicated by the letter “H”.

Weld All Around Symbol

The weld all around symbol indicates that the weld is to be made all around the joint. This is represented by a small circle at the intersection of the reference line and the arrow.

Field Weld Symbol

The field weld symbol indicates that the weld is to be made on-site, rather than in the fabrication shop. It is represented by a small flag at the intersection of the reference line and the arrow.

Melt-Through Symbol

The melt-through symbol indicates that complete joint penetration is required and that the weld must penetrate through the entire thickness of the joint. This symbol is often used in combination with groove weld symbols.

Butt Weld Symbol

The butt weld symbol represents a weld used to join two pieces of metal end-to-end in the same plane. Butt welds are commonly used in pipe welding, structural welding, and other applications where a strong, continuous joint is required.

Characteristics of Butt Welds

• Joint Type: End-to-end joint in the same plane.
• Applications: Pipe welding, structural welding, and pressure vessels.
• Symbol Representation: A simple line placed on the reference line, with additional details such as groove type and weld size.

Socket Weld Symbols

Socket welds are used to join pipes and fittings in various industries, including plumbing, gas distribution, and petrochemical plants. They are particularly useful for high-pressure systems due to their ability to create strong, leak-proof joints. Understanding socket weld symbols is crucial for welders and engineers to ensure these welds are performed correctly and meet the required specifications.

Characteristics of Socket Welds

1. Joint Preparation: Involves inserting the pipe into a recessed area of a fitting and welding around the joint.
2. Applications: Common in high-pressure piping systems, including plumbing, gas distribution, and chemical processing.
3. Strength: Provides a strong, leak-proof joint capable of withstanding high pressures.
4. Ease of Use: Requires less alignment than butt welds, making them easier to install.

Anatomy of Socket Weld Symbols

Socket weld symbols include several elements that provide detailed instructions for creating these welds. These elements include the reference line, arrow, basic weld symbol, and additional details such as the size of the weld and any specific requirements.

Components of Socket Weld Symbols

• Reference Line: The main horizontal line that serves as the base of the welding symbol.
• Arrow: A line that connects the reference line to the joint where the weld is to be made. The arrow points to the location of the weld.
• Basic Weld Symbol: Indicates the type of socket weld.
• Size and Dimensions: Details such as weld size and socket depth.
• Supplementary Symbols: Additional symbols that may indicate specific requirements or finishing processes.
• Tail: Optional; used to include additional instructions or references to welding procedures.

Types of Socket Welds and Their Symbols

The symbol for socket welds is a simplified representation compared to other types of weld symbols. The main component of the socket weld symbol is a representation of the socket and weld around the pipe.

Example of a Basic Socket Weld Symbol

The basic socket weld symbol typically includes a rectangular or square symbol representing the socket and a fillet weld symbol indicating the type of weld around the joint.

• Symbol: A square or rectangle with a fillet weld symbol on the reference line.

• Reference Line: The horizontal line running through the symbol.
• Arrow: Points to the location of the socket weld.
• Square/Rectangle: Represents the socket joint.
• Fillet Weld Symbol: Indicates a fillet weld around the socket joint.

Reading Socket Weld Symbols

The socket weld symbol consists of a square or rectangle representing the socket joint and a fillet weld symbol indicating the type of weld to be applied around the joint. Additional details such as the size of the weld or any specific requirements can be included.

Basic Example

Consider a simple socket weld symbol with a reference line, an arrow, a square/rectangle, and a fillet weld symbol.

• Reference Line: The horizontal line running through the symbol.
• Arrow: The line connecting the reference line to the location of the socket weld.
• Square/Rectangle: Represents the socket joint.
• Fillet Weld Symbol: Indicates a fillet weld around the joint.

IV. Application of Welding Symbols in Drawings

Welding symbols are used in engineering drawings to provide clear and standardized instructions for making welds. These symbols convey crucial information such as the type, size, location, and any additional specifications for the welds.

Key Elements of Welding Symbols in Drawings:

• Reference Line: The main horizontal line that serves as the base of the welding symbol.
• Arrow: A line that connects the reference line to the weld location.
• Tail: An optional part of the welding symbol that can include additional information.
• Basic Weld Symbols: Indicate the type of weld required.
• Supplementary Symbols: Provide additional details about the weld.

Understanding the various types of welding symbols is essential for anyone involved in the welding industry. These symbols provide standardized instructions that ensure welds meet design and safety standards. By mastering welding symbols, welders, engineers, and inspectors can ensure the quality and integrity of welded structures, leading to safer and more reliable products.