PAUT Procedure Requirements: A Complete Guide for ASME and ISO Compliance

Why PAUT Procedures Are Held to a Higher Standard

Phased Array Ultrasonic Testing (PAUT) is more powerful than conventional UT — but that power comes with greater complexity and correspondingly stricter procedural requirements. A conventional UT procedure might be 5–10 pages. A rigorous PAUT procedure, with all required focal law calculations, scan plan documentation, calibration block specifications, and sector-qualification details, can easily run 20–40 pages.

This complexity means PAUT procedures fail review more often. They also attract more scrutiny from client Level 3 engineers, third-party inspection firms, and regulatory inspectors. Getting a PAUT procedure right the first time is critical for project timelines.

Governing Standards for PAUT Procedures

Depending on your application, one or more of these will apply:

• ASME Section V Article 4: General UT requirements, including PAUT as a technique
• ASME Section V Mandatory Appendix III: Specific PAUT requirements added in recent editions
• ASME Code Case 2235: PAUT as an alternative to RT for weld examination in pressure vessels
• ISO 13588:2019: Ultrasonic testing using phased array technique — procedure requirements
• EN ISO 13588: European equivalent, used in CE-marked equipment fabrication
• ASTM E2700: Standard practice for contact UT using phased array (US)
• Client specifications: Many major operators (BP, Shell, Saudi Aramco, etc.) have their own PAUT specifications that supplement the above

Mandatory PAUT Procedure Elements Under ASME

1. Hardware Specification

PAUT procedures must specify the instrument to a greater level of detail than conventional UT:

• Instrument make, model, and minimum number of active channels
• Pulser/receiver frequency range and pulse repetition frequency (PRF)
• Software version (for encoded data acquisition)
• Encoder type and resolution (if mechanised)

2. Probe (Array) and Wedge Specification

This is one of the most frequently incomplete sections:

• Array type (linear, matrix, annular) and number of elements
• Element pitch and aperture
• Nominal frequency and bandwidth
• Near-field length (N) calculation or reference
• Wedge make and model, Rexolite or equivalent material specification, wedge angle
• Wedge wear limit and inspection criteria
• Couplant type and application method

3. Focal Laws and Angular Range

This is unique to PAUT and has no equivalent in conventional UT procedures. You must document:

• Software used to calculate focal laws (name and version)
• Steering angles range (e.g., 40°–70° in 1° increments)
• Aperture (number of active elements per focal law)
• Focal depth or focal range
• Justification that the angular range provides adequate coverage of the required examination volume (often supported by a ray-tracing calculation or coverage plot)

4. Calibration Blocks

PAUT requires additional calibration blocks beyond conventional UT:

Every calibration block must be fully described in the procedure: drawing number or dimensional sketch, material specification (matching base metal), heat treatment condition, and surface finish requirements.

5. Scan Plan and Coverage Documentation

For encoded (mechanised) PAUT, the scan plan must include:

• Scan direction(s) and scanning surface(s)
• Index point placement relative to weld centreline
• Scan increment (encoder resolution)
• Scan overlap between adjacent passes
• Scanner speed limit (if encoder is used — over-speed can result in missed data)
• Weld geometry (groove angle, root configuration) — confirmed match to examination volume

6. Data Recording and Reporting

PAUT generates large datasets (A-scans, S-scans, C-scans). Your procedure must state:

• Recording threshold (typically 20% or 40% FSH depending on code)
• Data format and software required to read/review data
• Data storage requirements and retention period
• Minimum content of examination reports (job identification, component ID, calibration block ID, operator certification, date, instrument serial number, data file reference)

Personnel Qualification — Sector-Specific PAUT Certification

This is a critical area where PAUT procedures frequently fail. Under ISO 9712, there are specific sector codes for advanced methods. A person qualified as "UT Level 2 Welds" under ISO 9712 is not automatically qualified for PAUT — they need a separate PAUT qualification.

Your procedure must state both the method (UT) and the technique (PAUT) in the qualification requirement:

• "Personnel shall hold a minimum UT Level II certification per ASNT SNT-TC-1A with demonstrated PAUT experience per the company Written Practice."
• Or: "Personnel shall hold a minimum ISO 9712 UT Level 2 certification with PAUT sector qualification for [Welds / Austenitic / Dissimilar Metal Welds] as applicable."

Most Common PAUT Procedure Non-Compliances

• Missing volumetric coverage demonstration — No ray-trace or software plot showing the inspection volume is covered
• Focal law justification absent — Angular range and aperture stated but no calculation showing adequacy
• Calibration block not described — SDH depths and spacings not stated; only "ASME basic calibration block" mentioned
• Personnel qualification incomplete — UT Level II stated without PAUT-specific qualification requirement
• Scanner speed not limited — For encoded systems, no maximum scan speed stated (data gaps possible above encoder capability)
• Data storage format not specified — No statement of proprietary format, software version needed for review, or backup requirements
• Code Case 2235 not acknowledged — Used for RT replacement weld examination but the code case applicability is not stated