Overview
ISO 16823:2012 - Non‑destructive testing - Ultrasonic testing - Transmission technique defines the principles and practical requirements for ultrasonic transmission techniques used to detect imperfections and to determine material attenuation. The standard is targeted at examinations of flat products (plates, sheets) and is applicable where direct reflection is unsuitable - e.g., in thin products, high‑attenuation materials, or when imperfection orientation is unfavourable for reflection.
Key topics and technical requirements
- Principle: transmission uses either two transducers (separate transmitter and receiver) or a single transducer with back‑wall reflection to evaluate the transmitted ultrasonic signal amplitude or time‑of‑flight.
- Probe configurations: straight‑beam and angle‑beam, contact, immersion, local immersion (squirter) and wheel probes are described for various set‑ups.
- Coupling and alignment: coupling quality and probe angulation critically affect transmitted amplitude; immersion or squirter scanning is recommended to improve coupling uniformity. Surface dressing may be necessary for contact scanning.
- Detection capability: an imperfection (or group) must intercept a significant portion (typically 25%–50% of the ultrasonic beam cross‑section) before a reliable amplitude change is seen. Transmission provides proof of absence along the sound path but does not give depth location.
- Sensitivity setting and scanning: sensitivity shall be set using a reference block of similar dimensions/surface/ultrasonic properties or a known flaw‑free area; manual testing recommends ~80% full screen height for transmitted signal. Scanning must maintain probe alignment.
- Evaluation of imperfections: procedures include confirming signal loss is not due to coupling/geometry, measuring maximum amplitude reduction, assessing affected volume and continuity, and plotting extent (e.g., 6 dB drop mapping).
- Attenuation measurement: attenuation is expressed as an attenuation coefficient (dB/m). ISO 16823 describes two measurement methods - a comparative technique using a reference block and a direct immersion technique using multiple echoes - and provides the necessary equations and measurement conditions.
Applications
- Inspection of plates and sheets, laminations and planar defects
- Testing thin components or materials with high ultrasonic attenuation
- Quality control in steel, aluminum, aerospace, shipbuilding, and manufacturing where through‑thickness continuity or material attenuation must be quantified
- Thickness verification where pulsed transmission is appropriate
Who should use this standard
- NDT technicians and inspection engineers implementing ultrasonic transmission tests
- Quality managers and metallurgists specifying inspection methods
- Test procedure authors and trainers developing transmission‑technique protocols
Related standards
- ISO 16810 - Ultrasonic testing: General principles
- ISO 16811 - Sensitivity and range setting
- ISO 16826 / 16827 / 16828 - Related ultrasonic examination and sizing methods
Keywords: ISO 16823:2012, ultrasonic testing, transmission technique, non‑destructive testing, attenuation, plates and sheets, transmission ultrasonic inspection.
