Overview
ISO 5178:2019 specifies the procedure and specimen sizes for the longitudinal tensile test on weld metal taken from fusion welded joints. It is a destructive test method used to determine the mechanical properties of weld metal in metallic materials and applies to joints produced by any fusion welding process, provided joint dimensions permit cylindrical specimens as defined by ISO 6892‑1. The test is carried out at room temperature (10 °C to 35 °C) with controlled tests typically at 23 °C ± 5 °C.
Key topics and technical requirements
- Specimen geometry: Cylindrical specimens with circular cross-section; nominal parallel diameter d0 = 10 mm, minimum 4 mm if 10 mm is not achievable. Dimensions otherwise follow ISO 6892‑1.
- Location and machining: Specimens must be taken longitudinally from the weld metal, normally from the weld centre. For thick or double-sided joints multiple specimens at different depths (t1, t2) may be taken and recorded.
- Extraction rules:
- For steel: shearing not permitted for thicknesses > 8 mm; thermal cutting is restricted and must be ≥ 8 mm from the final parallel length; thermal cutting must not be parallel to the original surface.
- For other metallic materials: shearing and thermal cutting are excluded; use machining methods such as sawing or turning.
- Surface quality: Tolerances and surface requirements conform to ISO 6892‑1; avoid strain hardening and excessive heating during preparation.
- Testing procedure: Apply an increasing tensile load continuously until rupture in accordance with ISO 6892‑1 principles.
- Fracture examination: After rupture, inspect and record imperfections (type, size, quantity); note fish eyes and consider only their central regions as imperfections.
- Test report requirements: In addition to ISO 6892‑1 data, include reference to ISO 5178, specimen location (sketch if needed), test temperature, observed imperfections, and actual specimen diameter.
Applications and practical value
- Ensures reliable assessment of weld metal tensile strength, elongation and fracture behaviour for quality control, qualification and failure analysis.
- Used in weld procedure qualification, production testing, material research, and certification of welded fabrications.
- Valuable for industries where welded integrity is critical: oil & gas, pressure vessels, shipbuilding, structural steel, aerospace and heavy fabrication.
Who uses this standard
- Welding engineers and metallurgists
- Welding inspectors and quality control laboratories
- Testing laboratories performing tensile testing on welds
- Fabricators and certification bodies involved in weld procedure and welder qualification
Related standards
- ISO 6892‑1 - Metallic materials - Tensile testing - Method of test at room temperature (normative reference used throughout ISO 5178)
- ISO/TC 44 (Welding and allied processes) provides broader context for weld testing standards
Keywords: ISO 5178, longitudinal tensile test, weld metal, fusion welded joints, destructive tests, tensile testing, ISO 6892-1, weld inspection.