Table of Content
Welding symbols are a crucial aspect of the welding process and Non-Destructive Evaluation (NDE), serving as a universal language that communicates important information about the weld joint to welders, inspectors, engineers, and other stakeholders involved in the fabrication process. Whether it's indicating the type of weld, size of the weld, or specific requirements for the joint, welding symbols provide clear instructions that help prevent errors and ensure consistency in the welding process.
Understanding welding symbols and meaning is essential for ensuring the integrity and quality of welded structures. Without a solid grasp of NDT with welding symbols, misinterpretations can lead to costly mistakes and compromise the safety and functionality of the final product.
What are the basic types of welding symbols?
Some of the common basic weld symbols are fillet welds, groove welds, spot welds, projection welds, and more." at the beginning of this section. Weld symbols are graphical representations used on engineering drawings to convey essential information about Welded Joints and welding processes. There are a few basic welding symbols, that are universally understood within the engineering and welding industries. Welding symbols in drawings provide a concise and standardised way to communicate welding requirements.
Weld symbols are shorthand for describing the type of weld, its size, and other processing and finishing information. These symbols indicate the welding processes used in metal joining operations, whether the weld is localized or 'all around,' whether it is a shop or field weld and the contour of welds. Here is a list of various weld symbols on drawings:
- Tack Weld Symbol
- Groove Weld Symbol
- Plug Weld Symbol
- Spot Weld Symbol
- Stitch Welding Symbol
- Fillet Weld Symbol
- Butt Weld Symbol
- Field Weld Symbol
1. Tack Weld Symbol
The tack weld symbol is a temporary weld used to hold components in place before final welding.
Example:
In the fabrication of a steel structure, tack welds are used to temporarily hold the structural components in place before the final welding. For instance, when assembling the framework of a steel building, tack welds are applied at key connection points to ensure proper alignment and stability during the welding process.
2. Groove Weld Symbol
Groove weld symbols are used to fill a groove between two pieces of metal. The symbol indicates the type of weld needed, such as a square or V-shaped groove. It also specifies the weld size and other important details for the welder to follow during fabrication.
Example:
In the construction of a Pressure Vessel, groove welds are used to join the cylindrical shell to the end caps. The groove welds fill the grooves between the components, providing a strong and leak-proof connection that can withstand high pressure.
3. Plug Weld Symbol
The plug weld symbol is a circular weld made through a hole in one of the workpieces, joining it to the surface of another workpiece beneath it. The plug weld symbol itself is a rectangle with a diameter symbol placed to the left of the symbol, as well as the number associated with that diameter. These welds are typically used to secure two pieces of metal together at a specific distance apart. The size and spacing of the plug weld are specified on the welding symbol to ensure proper alignment and strength of the joint.
A plug weld, also known as a rosette weld, is a process that fuses two metals together by making a weld inside small circular holes.
Example:
In automotive manufacturing, plug welds are commonly used to attach body panels to the vehicle's frame. Small holes are drilled in the panels, and plug welds are then applied through these holes, securely fastening the panels together.
4. Spot Weld Symbol
Spot weld symbols are made by applying pressure and electrical current to two or more layers of metal, creating a weld at specific points. These welds are commonly used in the automotive and sheet metal fabrication industries due to their speed and efficiency.
Example:
In the production of sheet metal components, spot welding is extensively used to join metal sheets together. For example, in the manufacturing of car bodies, spot welds are applied at specific points along the seams of the panels, creating a strong and durable bond.
5. Stitch Welding Symbol
The stitch welding symbol involves making a series of intermittent welds along a joint instead of a continuous weld. This is typically used for thinner materials or when a continuous weld is not necessary. The stitch weld symbol consists of a series of evenly spaced dots, or short dashes, along the length of the joint line.
Advantages of Stitch Welding:
Stitch welding offers several benefits, such as minimizing material warping, reducing welding time, and saving on material costs compared to continuous welding. It is particularly advantageous in applications requiring less structural stress.
Symbol Representation:
The stitch weld symbol is often annotated on technical drawings with details like the pitch (distance between adjacent weld centers) and weld segment length.
Example:
In the construction of storage tanks, stitch welding is employed to join the tank plates together. Instead of continuous welding along the entire length of the seam, stitch welding involves making intermittent welds at regular intervals, reducing distortion and heat input while ensuring structural integrity.
Other Applications:
Stitch welding is also widely used in automotive chassis fabrication, HVAC ductwork, and lightweight metal constructions.
Challenges in Stitch Welding:
Despite its advantages, stitch welding may not provide the same strength as continuous welding and requires thorough inspection to ensure uniform quality at each weld segment.
6. Fillet Weld Symbol
Fillet weld symbol are triangular in cross-section and are used to join two pieces of metal at right angles to each other. The symbol for fillet welding consists of a triangle drawn along the joint line, with the size of the weld specified inside the triangle.
Example:
In the fabrication of steel structures, fillet welds are used to join beams to columns. The triangular fillet welds are applied at the intersection of the beams and columns, providing a strong and reliable connection capable of withstanding structural loads.
7. Butt Weld Symbol
Butt weld symbol join two pieces of metal along their edges in a single plane. The symbol for butt welding consists of two parallel lines drawn along the joint line, with the size of the weld specified between or below the lines.
Example:
In pipeline construction, butt welds are used to join sections of pipe together. The ends of the pipes are aligned and welded along their edges in a single plane, creating a seamless and leak-proof connection suitable for transporting fluids or gases.
8. Field Weld Symbol
Field weld symbols are welds made on-site during construction or installation rather than in a controlled environment like a workshop. These welds are typically indicated on engineering drawings with a field weld symbol, which specifies the location and type of weld needed for proper construction. Field welds are crucial for connecting structural elements in large-scale projects such as bridges or buildings.
Example:
In the construction of steel bridges, field welds are applied on-site to connect prefabricated steel components. For instance, field welds are used to join the bridge girders to the supporting piers, allowing for efficient assembly and installation of the bridge structure.
These symbols are essential for communicating welding requirements effectively on engineering drawings and blueprints, ensuring consistency and clarity in Welding Processes. Understanding these basic weld symbols is essential for engineers, welders, and other professionals involved in fabrication and manufacturing processes. They facilitate clear communication of welding requirements, ensuring consistency, accuracy, and quality in welding operations.
Welding Symbols in NDT
Weld symbols play a crucial role in non-destructive testing by providing essential information about the weld joint and the requirements for inspection. These symbols are used to communicate the type of weld, its size, and any additional information necessary for ensuring the quality of the weld.
Understanding weld symbols is essential for welders, inspectors, and engineers involved in the fabrication process. This includes symbols such as Plug, Slot, Arc Spot, Arc Seam, Resistance Spot, Resistance Seam, and Projection Welding Symbols, where the arrow connects the welding symbol reference line to the outer surface of one member of the joint at the center line of the desired weld. Here's why weld symbols are necessary in NDT:
Identification of Weld Joints
Weld symbols help NDT technicians identify the Location of Weld Joints on the workpiece. This is important because NDT techniques such as ultrasonic testing, radiographic testing, and magnetic particle testing need to be applied to specific areas of the weld to detect any defects accurately.
Understanding Weld Configuration
Weld symbols provide information about the configuration of the weld, including the Type of Weld Joints, weld size, and weld preparation details. This knowledge helps NDT technicians select the appropriate testing method and equipment for inspecting the weld effectively.
Interpretation of Inspection Results
NDT technicians use weld symbols to interpret the results of non-destructive testing accurately. By understanding the requirements specified in the weld symbol, technicians can determine whether detected indications or defects meet acceptance criteria or require further evaluation.
Quality Control and Assurance
Weld symbols serve as a communication tool between welding engineers, inspectors, and technicians, ensuring that everyone involved understands the welding requirements and inspection criteria. This helps maintain consistency in quality control and assurance processes, reducing the likelihood of errors or oversights during inspection.
Documentation and Reporting:
Weld symbols provide a reference point for documenting NDT inspection results. NDT reports typically include details about the welds inspected, the NDT Techniques used, and the location and size of any defects detected. Weld symbols help ensure that inspection reports accurately reflect the specific welds examined and the results obtained.
Compliance with Standards:
Weld symbols are often used to indicate the requirements of welding standards and codes, such as those established by organisations like the American Welding Society (AWS) or the International Organization for Standardization (ISO). Compliance with these standards is essential for ensuring the safety, reliability, and quality of welded components, making weld symbols integral to NDT processes.
What is the Welding Code?
In welding, Codes and Standards provide guidelines for welding processes to ensure the safety, integrity, and reliability of welded structures with different types of welding symbols. The welding code specifies essential parameters such as welding procedures with NDE techniques and NDT methods, preheat and interpass temperature requirements, welding consumables, inspection methods, and acceptance criteria for weld quality. Adhering to the welding code is critical for achieving welds that meet the specified design requirements and performance expectations.
One of the most influential welding codes is the American Welding Society (AWS) D1.1 Structural Welding Code – Steel. This code is specifically tailored to address the welding of structural steel components used in diverse applications, such as buildings, bridges, and other infrastructure. Now, let's see what this welding code entails:
Welding Procedures:
The code specifies detailed procedures to be followed during the Welding Process. This includes guidelines on the selection of welding methods, techniques, and parameters to achieve optimal results. To follow the process, the technician must know how to read weld symbols.
Preheat and Interpass Temperature Requirements:
Certain welding applications require preheating of the base metal and maintaining specific temperatures between welding passes to prevent cracking and ensure proper fusion. The welding code outlines precise preheat and interpass temperature requirements based on material composition and thickness.
Welding Consumables:
The selection of appropriate welding consumables, such as electrodes and filler metals, is critical for achieving welds with the desired mechanical properties. The welding code provides guidance on the types and specifications of consumables suitable for different welding applications.
Inspection Methods:
To assess the quality of welds, various inspection methods are employed. These methods range from Visual Inspection to more advanced techniques such as radiographic testing and ultrasonic testing. The welding code delineates the requirements for conducting inspections and interpreting the results accurately.
Acceptance Criteria for Weld Quality:
Welds must meet specific quality standards to ensure structural integrity and performance. The welding code defines acceptance criteria for weld defects, including permissible sizes of discontinuities and criteria for rejecting defective welds.
By following the guidelines outlined in the welding code, welders and inspectors can ensure that welded structures withstand the rigours of their intended applications, providing reliability and peace of mind to stakeholders.
Key Takeaways
- Welding symbols serve as a universal language for communicating welding information.
- NDT principles such as visual inspection, radiographic testing, ultrasonic testing, magnetic particle testing, and dye penetrant testing are essential for evaluating weld quality.
- Welding codes and standards provide guidelines for ensuring the safety, integrity, and reliability of welded structures.
FAQs
1. Why are welding symbols used?
A: Welding symbols are essential for communicating critical details about weld joints, including the type of weld, size, and placement. These symbols ensure that designers, engineers, and welders are on the same page, leading to consistent and accurate welds. By standardizing this information, welding symbols reduce errors, save time in manufacturing, and maintain product quality.
2. What is the weld size?
A: The weld's size is determined by leg length or throat thickness, accounting for material thickness and load-bearing requirements. Weld size refers to the dimensions of the weld cross-section, typically expressed in terms of its throat thickness or leg length.
3. Where is the weld symbol?
A: The weld symbol is usually found on welding drawings or blueprints next to the joint to be welded. It provides essential information such as weld type, size, and other welding requirements. The location of the symbol in relation to the reference line is important: if the weld is to be made on the arrow side of the joint, the symbol appears below the reference line, while for welds on the opposite side, it is placed above the reference line. Understanding this placement ensures proper execution of the weld in manufacturing.
References:
1. Meyer Tool & Manufacturing
2. Esierra
3. Open Oregon Educational Resources
4. Eng-Tips
5. Metalworkmasters.com
6. ElectronicsHub
7. ConceptDraw
