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ISO/TR 25901-4:2016 — Welding and Allied Processes — Vocabulary for Metallic Materials
Standardized Terminology for Arc, Resistance, Solid-State, and Thermal Cutting Processes in Metal Joining
1. Overview and Scope of the Standardized Welding Vocabulary
ISO/TR 25901-4:2016 is part of the multi-part Technical Report series that establishes a comprehensive vocabulary for welding and allied processes. This particular part focuses exclusively on terminology related to the welding of metallic materials, providing engineers, inspectors, researchers, and educators with a unified language for describing metal-joining techniques, equipment, defects, and testing methods.
The standardization of welding terminology is far from an academic exercise. In international engineering projects, miscommunication about process parameters, joint configurations, or defect classifications can lead to catastrophic weld failures. By adopting the vocabulary defined in ISO/TR 25901-4, project teams across different countries and disciplines can ensure mutual understanding of critical welding specifications.
When preparing welding procedure specifications (WPS) for international projects, always cross-reference your terminology against ISO/TR 25901-4 to avoid ambiguity in process descriptions and acceptance criteria.
The report covers vocabulary across the full spectrum of metal welding processes, including arc welding (submerged arc, gas metal arc, tungsten inert gas, plasma arc), resistance welding (spot, seam, projection, butt), solid-state welding (friction, ultrasonic, diffusion, explosion), and thermal cutting. Each term is defined with precision, often including notes on usage, synonyms, and relationships to related terms.
| Process Category | Key Processes | Common Applications | Critical Terminology Elements |
|---|---|---|---|
| Arc Welding | SMAW, GMAW, GTAW, SAW, PAW | Structural steel, pipelines, pressure vessels | Electrode classification, shielding gas, arc characteristics, penetration patterns |
| Resistance Welding | Spot, seam, projection, flash butt | Automotive body panels, wire mesh, battery tabs | Nugget formation, electrode force, weld time, expulsion criteria |
| Solid-State Welding | Friction stir, ultrasonic, diffusion, explosive | Aerospace structures, electronics packaging, dissimilar metals | Weld interface, plastic deformation zone, bonding temperature, intermetallic layer |
| Brazing and Soldering | Furnace brazing, induction brazing, wave soldering | Heat exchangers, HVAC systems, circuit boards | Filler metal flow, wetting angle, capillary clearance, joint gap |
| Thermal Cutting | Oxy-fuel, plasma, laser, water-jet | Plate cutting, pipe beveling, demolition | Kerf width, heat-affected zone, dross formation, cut surface quality |
2. Key Terminology Categories and Their Engineering Significance
The vocabulary in ISO/TR 25901-4 is organized into logical categories that reflect the structure of welding engineering knowledge. Understanding these categories helps engineers navigate the terminology systematically and apply it correctly in technical documentation.
Process-related terms form the largest category, covering the names of welding processes, process variants, and procedural parameters. For example, the report carefully distinguishes between gas metal arc welding (GMAW) and its subtypes including metal inert gas welding (MIG) and metal active gas welding (MAG), which use different shielding gas compositions that significantly affect weld metal chemistry and mechanical properties.
Do not use the terms MIG and MAG interchangeably. ISO/TR 25901-4 clarifies that MIG uses inert shielding gases (Ar, He) while MAG uses active gases (CO2, Ar-CO2 blends). Using the wrong gas type can lead to porosity, excessive spatter, or inadequate penetration.
Joint and weld-type terminology addresses the geometric classification of welded connections. Terms such as butt joint, fillet weld, lap joint, T-joint, and corner joint are defined along with their dimensional parameters. The report also standardizes terms for weld preparation features like bevel angle, root face, root gap, and included angle, which are essential for specifying joint designs in welding procedure qualification records (WPQR).
Defect and discontinuity terminology is particularly important for quality control and non-destructive testing (NDT). The report defines terms for common weld imperfections including porosity, slag inclusion, lack of fusion, incomplete penetration, undercut, overlap, crater cracks, and hydrogen-induced cold cracking. Each term is accompanied by descriptive notes that help NDT inspectors classify indications consistently during radiographic or ultrasonic examination.
Equipment and accessory terms cover welding power sources, wire feeders, torches, electrodes, and consumables. Standardized names for equipment components ensure that procurement specifications, maintenance manuals, and operator training materials use consistent language across manufacturers and jurisdictions.
3. Practical Applications in Welding Engineering and Quality Assurance
The practical value of ISO/TR 25901-4 extends across the entire lifecycle of welded construction, from design and material selection through fabrication, inspection, and in-service monitoring.
In design engineering, standardized terminology ensures that weld symbols on engineering drawings correspond unambiguously to the intended welding process and joint configuration. When a designer specifies a single-V butt weld with a 60-degree included angle and 2 mm root face, every fabricator reading the drawing interprets the requirement identically, regardless of their native language or regional training background.
Companies that adopt ISO/TR 25901-4 terminology in their welding documentation report 30-50% fewer requests for information (RFIs) during fabrication, as contractors no longer need to clarify ambiguous weld specifications.
In quality management systems for welding, the vocabulary provides the basis for writing clear non-conformance reports (NCRs), weld repair procedures, and acceptance criteria. When a quality inspector documents linear porosity exceeding 5% of weld length per ISO 5817, the use of standardized defect terminology prevents disputes between the fabricator and the client about the nature and severity of the indication.
For welding procedure qualification, the terms defined in this Technical Report appear directly in essential variables tables for WPQRs per ISO 15614 series standards. Process names, welding positions (PA, PB, PC, PD, PE, PF, PG per ISO 6947), and joint types must all use the standardized vocabulary to maintain qualification validity across projects.
In education and training, welding instructors rely on the ISO/TR 25901-4 vocabulary to structure curriculum content and assess student competency. International welding engineer (IWE) and international welding technologist (IWT) programs mandated by the International Institute of Welding (IIW) incorporate this terminology as a foundational knowledge requirement.
Frequently Asked Questions
Q1: How does ISO/TR 25901-4 differ from AWS A3.0 terminology?
ISO/TR 25901-4 is the international (ISO) standard for welding vocabulary focused on metallic materials, while AWS A3.0 is the American Welding Society standard. While many terms overlap, there are differences in preferred process names and definitions. For example, what AWS calls GMAW is the same as ISO gas metal arc welding, but some variant process names differ. Engineers working on international projects should specify which terminology standard governs their contract documents.
ISO/TR 25901-4 is the international (ISO) standard for welding vocabulary focused on metallic materials, while AWS A3.0 is the American Welding Society standard. While many terms overlap, there are differences in preferred process names and definitions. For example, what AWS calls GMAW is the same as ISO gas metal arc welding, but some variant process names differ. Engineers working on international projects should specify which terminology standard governs their contract documents.
Q2: Is ISO/TR 25901-4 applicable to robotic and automated welding?
Yes. The vocabulary includes terms relevant to mechanized, automated, and robotic welding processes. Terms such as welding robot, seam tracking, adaptive control, and welding parameter optimization are defined within the framework of the standard process terminology. This ensures that automation engineers and welding engineers can communicate effectively about process requirements.
Yes. The vocabulary includes terms relevant to mechanized, automated, and robotic welding processes. Terms such as welding robot, seam tracking, adaptive control, and welding parameter optimization are defined within the framework of the standard process terminology. This ensures that automation engineers and welding engineers can communicate effectively about process requirements.
Q3: How often is the welding vocabulary updated?
The ISO/TR 25901 series undergoes periodic review and revision to incorporate emerging welding technologies and processes. Part 4 was most recently confirmed in 2021. Engineers should always reference the current edition of the relevant part to ensure their terminology reflects the latest industry practice, particularly for newer processes like friction stir welding and hybrid laser-arc welding.
The ISO/TR 25901 series undergoes periodic review and revision to incorporate emerging welding technologies and processes. Part 4 was most recently confirmed in 2021. Engineers should always reference the current edition of the relevant part to ensure their terminology reflects the latest industry practice, particularly for newer processes like friction stir welding and hybrid laser-arc welding.
Q4: Can this vocabulary be used for additive manufacturing (DED) processes?
Yes, the terms for directed energy deposition (DED) additive manufacturing processes that use welding-based techniques (such as wire-arc additive manufacturing, WAAM) draw heavily on the vocabulary in ISO/TR 25901-4. The terminology for arc characteristics, deposition rates, and interpass temperatures is directly applicable to DED process development and qualification.
Yes, the terms for directed energy deposition (DED) additive manufacturing processes that use welding-based techniques (such as wire-arc additive manufacturing, WAAM) draw heavily on the vocabulary in ISO/TR 25901-4. The terminology for arc characteristics, deposition rates, and interpass temperatures is directly applicable to DED process development and qualification.
