A Guide to WPS Symbols: Understanding Weld Procedures and Quality
Welding Procedure Specifications (WPS) are critical documents that outline the specific parameters for a welding operation. They ensure consistency, quality, and repeatability in welding, regardless of the welder performing the task. Integral to a WPS are a series of symbols, abbreviations, and numerical representations that convey crucial information about the weld joint. Understanding these symbols is essential for anyone involved in welding, from welders and inspectors to engineers and designers. This comprehensive guide will dissect the various symbols used in WPS, providing a detailed explanation of their meaning and application.
1. Weld Type Symbols:
Weld type symbols are graphical representations of the desired weld configuration. They depict the joint geometry, weld location, and groove details. These symbols are standardized by organizations like the American Welding Society (AWS) and the International Organization for Standardization (ISO).
- Fillet Weld (Δ): Represents a triangular shaped weld used to join two pieces of metal at an angle. The symbol’s orientation indicates the weld’s location.
- Groove Weld (Various): Covers a range of weld types designed to fill a prepared groove between two members. Common groove weld symbols include:
- Square Groove ( ): A basic groove with parallel sides.
- Single-V Groove ( ): A V-shaped groove prepared on only one member.
- Double-V Groove ( ): A V-shaped groove prepared on both members.
- Bevel Groove ( ): An angled groove prepared on only one member.
- Double-Bevel Groove ( ): An angled groove prepared on both members.
- U-Groove ( ): A U-shaped groove prepared on only one member.
- Double-U Groove ( ): A U-shaped groove prepared on both members.
- J-Groove ( ): A J-shaped groove prepared on only one member.
- Double-J Groove ( ): A J-shaped groove prepared on both members.
- Plug Weld (◯): A circular weld used to join two overlapping members by filling a hole in one member.
- Slot Weld (▭): An elongated weld similar to a plug weld but with a rectangular or oval shape.
- Spot Weld (•): A small, localized weld typically used to join sheet metal.
- Seam Weld (– – –): A continuous weld made along a seam, often used in automated processes.
2. Supplementary Symbols:
These symbols provide additional information about the weld, such as its contour, finish, and penetration requirements.
- Weld All Around (◯): Indicates that the weld should be continuous around the entire joint.
- Field Weld (F): Specifies that the weld is to be performed at the construction site rather than in a workshop.
- Contour Symbols: These depict the desired shape of the weld bead.
- Flat (–): A flat weld surface.
- Convex (+): A slightly raised weld surface.
- Concave (-): A slightly indented weld surface.
- Finish Symbols: These indicate the required surface finish of the weld.
- Grinding (G): The weld surface should be ground smooth.
- Machining (M): The weld surface should be machined to a specific dimension.
- Chipping (C): Excess weld metal should be chipped away.
- Penetration Symbols: These specify the required depth of weld penetration.
- Complete Joint Penetration (CJP): The weld must penetrate the full thickness of the joint.
- Partial Joint Penetration (PJP): The weld penetrates only a portion of the joint thickness.
3. Dimensions and Tolerances:
WPS often includes numerical values to specify dimensions and tolerances for the weld. These include:
- Size (s): The leg length of a fillet weld or the depth of a groove weld.
- Root Opening (R): The gap between the members at the root of the joint.
- Groove Angle (A): The angle between the sides of the groove.
- Effective Throat (te): The minimum distance from the face of the weld to the root.
- Length (L): The length of the weld.
- Pitch (p): The distance between the centers of intermittent welds.
4. Welding Process and Parameters:
The WPS identifies the specific welding process to be used, along with the associated parameters. These include:
- Welding Process: Examples include Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), and Submerged Arc Welding (SAW).
- Current (A): The electrical current used during welding.
- Voltage (V): The electrical potential difference across the arc.
- Travel Speed (TS): The rate at which the welding electrode moves along the joint.
- Heat Input (HI): The amount of heat energy applied to the weld joint.
- Shielding Gas: The type of gas used to protect the weld pool from atmospheric contamination.
- Electrode/Filler Metal: The type and size of the electrode or filler metal used.
- Preheat Temperature: The temperature to which the base metal is heated before welding.
- Interpass Temperature: The maximum temperature allowed between successive weld passes.
- Post Weld Heat Treatment (PWHT): A controlled heating and cooling cycle applied to the weldment after welding.
5. Testing and Inspection Requirements:
WPS also specifies the required testing and inspection procedures to ensure weld quality. These might include:
- Visual Inspection (VT): Examining the weld for surface defects.
- Magnetic Particle Testing (MT): Detecting surface and near-surface cracks in ferromagnetic materials.
- Liquid Penetrant Testing (PT): Detecting surface cracks in non-magnetic materials.
- Radiographic Testing (RT): Using X-rays or gamma rays to detect internal flaws.
- Ultrasonic Testing (UT): Using high-frequency sound waves to detect internal flaws.
6. Reference Documents and Standards:
WPS often references relevant codes, standards, and other documents. These might include AWS D1.1 (Structural Welding Code – Steel), ASME Section IX (Welding and Brazing Qualifications), and API 1104 (Welding of Pipelines and Related Facilities).
7. Other Symbols and Abbreviations:
Various other symbols and abbreviations may be used in a WPS, depending on the specific application. It’s essential to refer to the relevant welding codes and standards for a complete understanding of these symbols. Some examples include:
- Backing Gas: A gas used to protect the back side of the weld.
- Root Face: The unfused portion of the groove face adjacent to the root.
- Bevel Angle: The angle of the bevel preparation.
Final Thoughts: Mastering WPS Symbolism
Understanding the symbols, abbreviations, and numerical representations within a WPS is paramount for producing high-quality, consistent welds. This guide has provided a comprehensive overview of the common symbols encountered, but continuous learning and referencing the appropriate standards are crucial for maintaining proficiency. By mastering WPS symbolism, welders, inspectors, and engineers can effectively communicate welding requirements, ensuring the integrity and safety of welded structures. Remember that staying updated with the latest revisions and amendments to relevant welding codes is vital for maintaining best practices and compliance within the industry. This ongoing commitment to knowledge will ultimately contribute to safer and more reliable welded fabrications.