Overview
ISO 16946:2024 - Non-destructive testing - Ultrasonic testing - Specification for a step wedge standard block - defines the material, dimensions and manufacturing requirements for a steel step wedge standard block used to set ultrasonic instruments. The third edition updates terminology (replacing “calibration block” with “standard block”), adds a CAD file link, and aligns Clause 4 with related ISO blocks.
Key topics and requirements
- Scope: Requirements for dimensions, material and manufacture of a steel step wedge standard block for setting ultrasonic instruments.
- Material: Steel grade S355J0 (EN 10025-2) or equivalent.
- Semi‑finished block: Recommended starting size before heat treatment: 320 mm × 120 mm × 30 mm.
- Heat treatment (required sequence):
- Austenitize at 920 °C for 30 min
- Rapid water quench
- Temper at 650 °C for 3 h
- Cool in still air
- Remove at least 2 mm from all surfaces after heat treatment
- Dimensional tolerances:
- Length and width: ±0.1 mm
- Step thickness: −0.02 mm for steps ≤ 12.5 mm; −0.1 mm for larger steps
- All external surfaces machined to surface roughness R ≤ 0.8 µm
- Ultrasonic verification and homogeneity:
- Internal discontinuity check after heat treatment using a longitudinal wave probe (≥10 MHz, 10–15 mm transducer)
- Set gain to produce grain scatter noise at 10% of screen height
- No internal echo amplitude greater than grain scatter noise
- Sound velocity requirements:
- Longitudinal wave velocity in step thickness direction v_l = (5920 ± 30) m/s
- Velocity determination accuracy: ±0.2% (±12 m/s)
- For reliable velocity measurement, larger rectangular blocks (thickness > 25 mm) are recommended
- Marking & documentation:
- Permanent reference marks, manufacturer name/logo, ISO number (ISO 16946) and unique serial number
- Manufacturer must issue a statement of conformity including the measured longitudinal wave velocity
Applications and users
- Primary use: setting the time base and sensitivity of ultrasonic test equipment during practical inspection work.
- Typical users:
- NDT laboratories and inspection teams
- Ultrasonic equipment manufacturers and service/calibration providers
- Suppliers of standard blocks and calibration accessories
- Quality and compliance departments in industries using ultrasonic testing
- Note: the step wedge block is intended to check certain instrument characteristics and assist in instrument setup, not to fully calibrate or validate all instrument performance.
Related standards
- ISO 2400 - Calibration block No. 1 (reference for large rectangular block and velocity determination)
- ISO 7963 - Calibration block No. 2
- ISO 19675 - Calibration block for phased array testing (PAUT)
- ISO 5577 - Ultrasonic testing vocabulary
- EN 10025-2 - Steel grade S355J0 technical delivery conditions
Keywords: ISO 16946:2024, step wedge standard block, ultrasonic testing, non-destructive testing, NDT, S355J0, sound velocity, surface roughness, calibration block.
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