Overview
ISO 3690:2018 - "Welding and allied processes - Determination of hydrogen content in arc weld metal" specifies standardized sampling and analytical procedures for measuring diffusible hydrogen in weld metal produced by arc welding with filler materials. It applies to martensitic, bainitic, and ferritic steels and covers collection methods (mercury displacement and inert‑gas headspace with thermal conductivity detection), temperature control to avoid release of non‑diffusible hydrogen, and calculation and reporting of hydrogen content in deposited or fused weld metal.
Key topics and requirements
- Scope and principle
- Measurement of diffusible hydrogen released from controlled weld specimens.
- Quantification by displaced volume (mercury method) or detector response (thermal conductivity).
- Specimen production and welding
- Standard test‑coupon geometries and fixture requirements to ensure repeatable weld deposits.
- Welding procedures for different arc processes, including specific handling for run‑on/run‑off pieces.
- Specimen handling and storage
- Rapid quenching and controlled storage (e.g., ≤ −78 °C) to prevent hydrogen loss prior to analysis.
- Cleaning, slag removal, and traceability (engraving/numbering and mass measurement).
- Hydrogen collection and measurement
- Mercury displacement technique: collection by displacing mercury and measuring volume.
- Headspace/thermal conductivity technique: collection into inert gas (argon) and detection by thermal conductivity.
- Temperature control during collection to avoid activation of non‑diffusible hydrogen.
- Quality assurance
- Calibration, linearity checks, calculations for diffusible hydrogen per mass or per weld volume, and reporting rules.
- Annexes providing guidance on older glycerine/mercury methods and information on accuracy/reproducibility.
Applications and who uses it
ISO 3690:2018 is used to:
- Verify hydrogen levels in welding consumables and procedures to reduce risk of hydrogen‑induced cracking (HIC) and cold cracking.
- Support welding procedure qualification, consumable development, and quality control in fabrication industries (pressure vessels, pipelines, heavy fabrication).
- Provide test methods for materials laboratories, welding engineers, quality managers, welding consumable manufacturers, certification bodies, and technical institutes (e.g., IIW members).
Related standards
- ISO 14175 - gases and gas mixtures for fusion welding (referenced normative).
- ISO/TR 17671‑1 - recommendations for welding of metallic materials (general guidance).
- Notes: ISO 3690:2018 was prepared by the International Institute of Welding (IIW) and includes cross‑references to historical methods (glycerine/mercury) for comparison purposes.
Keywords: ISO 3690:2018, diffusible hydrogen, weld metal, arc welding, mercury displacement, thermal conductivity detector, welding test specimen, welding consumables, hydrogen content measurement.
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