Overview
ISO 16809:2017 - "Non-destructive testing - Ultrasonic thickness measurement" defines the principles and practical requirements for measuring material thickness by ultrasonic time-of-flight (TOF) techniques. Applicable to metallic and non‑metallic materials, the standard covers direct-contact ultrasonic methods and specifies modes, instrument types, probes, couplants, reference blocks, operator qualification and reporting conventions.
Key topics and technical requirements
- Measurement principle: Thickness is calculated from the measured transit time of ultrasonic pulses multiplied by the material sound velocity and adjusted for pulse transit count (single-echo, multiple‑echo, delay-line or through‑transmission modes).
- Measurement modes: Mode 1 (single-echo), Mode 2 (single-echo with delay line), Mode 3 (multiple-echo), Mode 4 (through-transmission).
- Instruments: Defines suitable instrument types - dedicated thickness gauges (with numeric display), gauges with A‑scan waveform display, and A‑scan instruments used for thickness readout.
- Probes and couplant: Requires appropriate longitudinal-wave probes (dual-element or single-element) and suitable couplant to ensure acoustic contact.
- Reference and test object requirements: Use of reference blocks and consideration of surface condition, coatings, geometry and material differences are specified.
- Environmental and special conditions: Guidance for measurements at low/high temperatures and in hazardous atmospheres.
- Instrument setting and verification: Procedures for setting instruments (digital and A‑scan) and for routine checks of settings.
- Accuracy influences: Detailed factors affecting accuracy - surface condition, temperature, coatings, geometry, resolution, range and material properties (inhomogeneity, anisotropy, attenuation).
- Reporting: Minimum content for test reports, including measurement data and general information.
Applications and users
ISO 16809:2017 is used to support reliable ultrasonic thickness measurement in manufacturing, maintenance and inspection contexts. Typical users include:
- NDT technicians and inspection engineers
- Quality assurance managers
- Asset integrity and corrosion engineers
- Industries: oil & gas, petrochemical, power generation, shipbuilding, aerospace, heavy manufacturing
Practical uses:
- In‑service residual wall thickness measurement of pipes and vessels
- Quality control during manufacture
- Corrosion monitoring and remaining life assessment
Related standards
- ISO 5577 - vocabulary for ultrasonic testing (terminology referenced by ISO 16809).
- ISO/TC 135 (NDT) publications and other ultrasonic testing standards may be referenced for complementary guidance.
Keywords: ultrasonic thickness measurement, non-destructive testing, ultrasonic testing, time of flight, A-scan, dual-element probe, single-element probe, couplant, thickness gauge.
