Overview
EN ISO 16826:2025 - Non-destructive testing - Ultrasonic testing - Testing for discontinuities perpendicular to the surface (ISO 16826:2025) defines principles and guidance for ultrasonic inspection methods aimed at detecting discontinuities that are perpendicular or nearly perpendicular to a surface. The standard focuses on two main ultrasonic approaches: the tandem technique and the longitudinal-longitudinal-transverse (LLT) technique, and provides practical guidance for testing metallic materials with thicknesses from 40 mm to 500 mm and with parallel or concentric surfaces.
Key topics
- Scope and applicability
- Detection of embedded planar discontinuities perpendicular to the surface.
- Primary guidance for metallic components (40–500 mm); can be adapted for other materials or thicknesses with documented procedures.
- Techniques described
- Tandem technique: use of two probes (transmitter and receiver) with intersecting beam axes to form a test zone; guidance on probe positioning, beam angles, probe movement and sensitivity settings.
- LLT technique: longitudinal-longitudinal-transverse wave method for similar discontinuity orientations; includes time base, depth determination and sensitivity diagrams.
- Test setup and personnel
- References ISO 16810 for general ultrasonic testing equipment and personnel requirements.
- Guidance on probe selection, beam angles, and special considerations for thick sections (>160 mm) or non‑planar surfaces.
- Calibration and evaluation
- Time base and sensitivity settings, depth‑gain diagrams, sensitivity corrections.
- Annex material (nomograms) for tandem distances on convex and concave surfaces.
- Advanced methods
- Application notes for phased array techniques as alternatives to conventional probes, with recommendation for additional verification steps when used.
Applications
- Used by organizations performing ultrasonic NDT of thick metallic components with parallel or concentric surfaces (e.g., plates, rings, forgings and cylindrical parts).
- Applicable for detecting embedded planar discontinuities such as delaminations, laminations or cracks that are perpendicular to the surface.
- Intended users: NDT technicians, inspection engineers, quality managers, inspection bodies and asset owners specifying ultrasonic acceptance criteria.
Related standards
- ISO 16810 - Ultrasonic testing - General principles
- ISO 16811 - Sensitivity and range setting
- ISO 16823 - Through‑transmission technique
- ISO 16827 - Characterization and sizing of discontinuities
- ISO 16828 - Time‑of‑flight diffraction technique
EN ISO 16826:2025 is essential for organizations that require reliable procedures for ultrasonic detection of perpendicular discontinuities in thick metallic products and for teams integrating phased array or conventional tandem/LLT approaches into inspection programs.
