Overview
EN ISO 16946:2024 - Non-destructive testing - Ultrasonic testing - Specification for a step wedge standard block (ISO 16946:2024) defines the requirements for manufacture, material, dimensions and marking of a steel step wedge standard block used for setting ultrasonic instruments. Published by CEN/ISO in 2024, this standard replaces the 2017 edition and formalizes the term “standard block” (replacing “calibration block”).
Key topics and technical requirements
- Material: Manufactured from steel grade S355J0 (EN 10025-2) or an equivalent grade.
- Dimensions & tolerances: Block geometry is defined in the standard’s Figure 1 (CAD file available from ISO). Tolerances include:
- Length and width: ±0.1 mm
- Step thickness: −0.02 mm for steps ≤12.5 mm; −0.1 mm for larger steps
- Surface finish: All external surfaces machined to surface roughness R ≤ 0.8 µm.
- Manufacture & heat treatment: Recommended semi-finished block size and heat treatment sequence:
- Austenitizing at 920 °C for 30 min
- Rapid quenching in water
- Tempering at 650 °C for 3 h
- Air cooling; remove at least 2 mm from all surfaces after heat treatment
- Integrity and checking: Prior to final machining, the semi-finished block must be tested ultrasonically for internal discontinuities:
- Use a longitudinal wave probe, ≥10 MHz, transducer size 10–15 mm
- Set gain so grain scatter noise = 10% of screen height
- No internal echo amplitude may exceed grain scatter noise
- Wave velocity: Longitudinal wave velocity in thickness direction must be determined per ISO 2400, with a permissible uncertainty of ±0.2% (±12 m/s). Target value: v_l = (5920 ± 30) m/s.
- Marking & documentation: Each block must carry permanent reference marks (manufacturer name/logo, ISO 16946 number, unique serial) and be supplied with a statement of conformity including the measured longitudinal wave velocity.
Applications and users
- Used for setting time base and sensitivity of ultrasonic testing equipment during practical inspections.
- Practical users include:
- NDT service providers and inspection technicians
- Quality and NDT laboratories
- Manufacturers of ultrasonic inspection equipment
- Welding and fabrication industries requiring routine instrument checks
- Note: the step wedge standard block is intended for instrument setting/verification of some characteristics - not as a comprehensive instrument calibration device.
Related standards
- ISO 2400 - Calibration block No. 1 (longitudinal wave velocity measurement)
- ISO 7963 - Calibration block No. 2
- ISO 19675 - Calibration block for phased array testing (PAUT)
- ISO 5577 - Ultrasonic testing vocabulary
Keywords: EN ISO 16946:2024, step wedge standard block, ultrasonic testing, non-destructive testing, S355J0, surface roughness, longitudinal wave velocity, instrument setting.
