ISO 16946:2024

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.