Is phased array UT (PAUT) accepted under AWS D1.1:2025?

Yes. AWS D1.1:2025 includes provisions for PAUT as an alternative to conventional pulse-echo UT for structural welds. A written PAUT procedure is required, the equipment must be calibrated per the procedure, and the EOR typically must accept PAUT as an alternative before the project begins.

Does PAUT replace RT on structural welds?

PAUT replaces conventional UT, not RT — they address different defect types. PAUT, like conventional pulse-echo UT, is optimized for planar defects such as lack of fusion and cracks. RT is better suited for volumetric defects like porosity and slag inclusions. The NDE method specified in the contract documents controls what is acceptable.

What certification level does a PAUT operator need under AWS D1.1?

AWS D1.1 requires the UT operator to hold at least ASNT Level II certification in UT. For PAUT specifically, operators should also be qualified on the specific instrument and technique being used, since PAUT involves data acquisition and analysis tools beyond basic pulse-echo UT.

How does PAUT documentation differ from a conventional UT report?

PAUT generates electronic scan files — A-scans, B-scans, C-scans, and S-scans — stored alongside the inspection report. The written procedure must define how long those files are retained. This is more comprehensive than a conventional UT paper report, which records only the inspector's written findings.

Phased array UT for structural welds under AWS D1.1

Phased array UT is accepted under AWS D1.1 for structural welds. Here's what QC managers need to know about written procedures, calibration, scan coverage, and records.

Phased array ultrasonic testing (PAUT) has moved from aerospace and nuclear power into structural steel fabrication over the past fifteen years. On AWS D1.1 projects, PAUT is accepted as an alternative to conventional pulse-echo UT for volumetric examination of structural welds. For CWI and QC managers, understanding what the code requires — and what separates a compliant PAUT program from one that will draw comments during a third-party review — is increasingly important as more fab shops and NDE subcontractors adopt the technology.

What phased array UT does differently

Conventional pulse-echo UT uses a single-element transducer sending a fixed-angle beam into the weld. The operator sweeps the probe manually across the scan path and reads the A-scan display in real time, logging indication positions and amplitudes on paper.

PAUT replaces that single element with an array of individual piezoelectric elements that can be electronically steered and focused to multiple angles simultaneously. A single probe pass can sweep through a range of beam angles, generating a cross-sectional image — the sector scan, or S-scan — that maps the weld volume in one acquisition. The operator sees a visual picture of the weld cross-section rather than a time-amplitude trace.

The practical consequences: PAUT typically provides better defect sizing and characterization, faster inspection on long butt welds, and electronic scan data that functions as a permanent inspection image rather than a handwritten report. None of those advantages change the acceptance criteria, but they make PAUT attractive on production runs and where a thorough documented record is required by the owner.

What AWS D1.1:2025 requires for PAUT

AWS D1.1:2025 includes dedicated requirements for PAUT use on structural welds, covering the written procedure, equipment, operators, and acceptance criteria. The key requirements:

Written PAUT procedure. A site- or project-specific written procedure must exist before inspection begins. The procedure must document the instrument, probe configuration (number of elements, element pitch, wedge angle), beam angles used, reference calibration block details, scanning pattern, and how indications are characterized and recorded. This is more detailed than a conventional UT procedure and typically requires more lead time to prepare and get EOR acceptance.

Equipment calibration. The PAUT instrument and probe assembly must be calibrated against a reference block before each inspection shift, or per the frequency specified in the written procedure. Reference reflectors (typically side-drilled holes and/or notches of defined dimensions) verify amplitude response and beam angle accuracy. Calibration records are part of the inspection package.

Operator qualification. AWS D1.1 requires the UT operator to hold at least ASNT Level II in UT. PAUT is a specialty technique, and operators working with PAUT instruments and software should have documented training and qualification on the specific system used. The written procedure typically identifies the qualification basis for the operators.

Scan coverage documentation. The written procedure must demonstrate that the scanning plan provides coverage of the full weld cross-section, heat-affected zone (HAZ), and fusion faces. Gaps in beam angle coverage are the most common procedure deficiency flagged during pre-inspection review. Work this out during procedure development, not on the job site.

Acceptance criteria. PAUT on structural welds uses the same amplitude-based and length-based acceptance criteria as conventional UT under AWS D1.1. The S-scan image aids interpretation and characterization, but it does not alter the pass/fail threshold. An indication that exceeds the reference level amplitude by the applicable dB amount — or that exceeds the allowable length — is rejectable under the same criteria that apply to conventional UT.

For the conventional UT acceptance criteria framework, see UT acceptance criteria for AWS D1.1 structural welds.

PAUT vs. conventional UT: the practical differences

Inspection speed. On butt welds in plate, PAUT is typically faster. A single scan pass sweeping multiple angles covers what would require several separate probe manipulations with conventional UT. On long SAW butt welds or production runs with repetitive joint geometry, the throughput advantage can be significant.

Data record. PAUT generates B-scans (cross-sectional slices at each scan position), C-scans (top-view amplitude maps), and S-scans (sector scans showing beam angle coverage). These electronic files provide a complete, reviewable record of the inspection — not just the inspector's notes. That is a meaningful difference for owners or EORs who want to verify inspection quality after the fact, or for litigation-sensitive projects where the inspection record is evidentiary.

Complex geometry challenges. PAUT is straightforward on flat butt welds in plate. On tubular connections, nozzle welds, or joints with limited access, the PAUT procedure development is more involved and may require a performance demonstration test (PDT) to verify that the scan plan achieves adequate coverage. Do not assume PAUT is plug-and-play on every joint type — validate coverage during procedure development.

Capital and personnel cost. PAUT instruments and software cost more than conventional UT equipment. Qualified PAUT operators typically command higher field rates. On projects where the alternative is RT with radiation exclusion zones, extended exposure times for thick material, or significant schedule disruption, PAUT often wins on total inspection cost. On lighter material with straightforward RT access, the economics are less clear.

When PAUT makes sense on a D1.1 project

PAUT is a strong fit when:

Material is too thick for practical RT (above roughly 2 inches, RT setup time, film cassette positioning, and exposure time become burdensome).
The project site is an occupied building or working facility where radiation exclusion zones would disrupt operations.
The contract or owner requires a permanent, reviewable volumetric inspection record.
The EOR specifies that phased array data must be retained as part of the project record.
The NDE program includes many repetitive joints of the same geometry (economy of scale on procedure development and calibration).

For thinner material, single-pass PJP welds, fillet welds, or projects where RT is already specified and there is no access problem, the choice is less clear. Coordinate with your NDE subcontractor during the bidding and planning phase — not after production welding starts.

The NDE method decision: where PAUT fits

PAUT detects subsurface planar defects with high sensitivity. It is not optimized for surface discontinuities — those require MT or PT. It is also not a substitute for RT when the contract requires a radiographic record for regulatory, insurance, or owner retention reasons.

When deciding between RT, UT (conventional or phased array), MT, and PT, the method choice starts with the defect types you're trying to detect, the joint geometry and material thickness, and the contract documents. See NDE method selection for structural welds for a full breakdown of method strengths and limitations.

Documentation: what PAUT adds to your inspection package

When PAUT is used on a D1.1 project, the inspection package for each weld should include:

Reference to the written PAUT procedure (by document number and revision)
Calibration records from the beginning of the inspection shift (or per procedure frequency)
Electronic scan files (B-scan, C-scan, S-scan) in a format specified by the procedure, retained for the project record period
Inspection report identifying weld number, operator, date, indication locations, amplitude relative to reference, length, and disposition (accept / repair-and-reinspect)
If expansion scope was triggered (indications found requiring additional inspection), records of all expanded inspections

The electronic scan files are what distinguishes PAUT record-keeping from a conventional UT report. They can be large and require organized storage. Ensure your document management system can retrieve them by weld ID during the retention period. See NDE documentation for the audit packet for what a complete NDE record set should contain.

Managing PAUT records alongside your WPS, PQR, and WPQ documents in one traceable system reduces the scramble at audit time. WPS Welding handles the full qualification and inspection record chain for structural fabricators.

Rule library based on AWS D1.1:2025; verify against your governing edition (the AHJ or contract may specify 2020 or earlier).