ISO 4773:2023

Overview - ISO 4773:2023 (Ultrasonic guided-wave testing using phased‑array)

ISO 4773:2023 provides guidance on using phased‑array ultrasonic guided‑wave testing (GW‑PA) for inspecting inaccessible structures - notably buried pipelines - made of carbon steel and stainless steel. The standard specifies a concept of application and an optimized process to obtain reliable test results on inaccessible pipe cases by adjusting beam patterns, focusing and steering guided waves, and tuning excitation time delays for array transducers. It does not prescribe general principles for underground facilities or redefine the phased‑array testing scheme in full; instead it focuses on practical application and process optimization for guided‑wave phased‑array NDT.

Key technical topics and requirements

• Scope and materials: Targeted at inaccessible structures including buried pipelines; materials considered are carbon steel and stainless steel.
• Personnel: Operators shall be qualified per ISO 9712 (Level 1 plus an additional 6 months training) or equivalent sector qualification; training on specific equipment is required.
• Principles: Use of phased‑array technology to achieve focusing and steering of guided waves by synthesizing phased beams via time delays between probe elements, improving signal‑to‑noise ratio in harsh/covered environments.
• Test equipment:
  • Frequency range: 20 kHz to 1 000 kHz.
  • Modes: longitudinal and torsional guided‑wave modes (apply multiple modes separately, not simultaneously).
  • Operation modes: pulse‑echo or pitch‑catch; instruments must support synthetic focusing and data display/recording.
  • Probe design: continuous ring or individual elements forming rings to produce axisymmetric waves; array arrangement and circumferential spacing inform excitation delays.
• Test procedure & setup:
  • Pre‑test prerequisites (coating removal for probe setup, access space, interference control).
  • Settings: sensitivity, range, DAC (distance amplitude curve) and TCG (time‑corrected gain).
  • Signal classification, periodic re‑checks and recording level management.
• Environmental considerations: Coating/cladding properties, soil quality, burial depth and moisture, pipe geometry (elbows, welds, supports).
• Periodic checks: Instrument inspection every 12 months (or after repairs/software updates); probe checks per ISO 18563‑3; system configuration verification using in‑service pipe references and checklist (Annex A).

Practical applications and users

ISO 4773:2023 is intended for:

• NDT engineers and inspectors performing guided‑wave phased‑array inspections on buried or otherwise inaccessible pipelines and piping.
• Pipeline operators and asset owners seeking improved coverage and reliability in inline and above‑ground integrity screening.
• NDT equipment manufacturers and software developers implementing phased‑array focusing/steering features.
• Inspection planners and maintenance teams who require standardized procedures for setup, data collection and reporting.

Benefits include improved signal‑to‑noise ratio, targeted focusing on suspected defects, and enhanced reliability in coated or buried conditions.

Related standards

• ISO 18211 - Guided‑wave testing of above‑ground pipelines
• ISO 23243 - Ultrasonic testing with arrays - Vocabulary
• ISO 5577 - Ultrasonic testing - Vocabulary
• ISO 9712 - Qualification and certification of NDT personnel
• ISO 18563‑3 - Periodic checks for phased‑array probes

Keywords: ISO 4773, phased‑array, ultrasonic guided‑wave testing, guided waves, NDT, buried pipelines, carbon steel, stainless steel, focusing, steering, DAC, TCG, ISO 9712.