Phased Array Ultrasonic Testing (PAUT)

PAUT is an advanced ultrasonic technique using a multi-element transducer (16–256 elements) with electronic beam steering and focusing, producing sectorial, linear, and compound scans for superior weld inspection and defect characterization.

Definition

Phased Array Ultrasonic Testing (PAUT) uses a probe containing many small piezoelectric elements that can be pulsed individually with controlled time delays. By varying the delays, the resulting beam is steered, focused, or scanned electronically without physical probe movement.

Technical Context

Common scan modes include the S-scan (sector scan), L-scan (linear scan), and compound scans combining multiple angles. PAUT data is typically captured with an encoder and stored for offline analysis, replay, and audit. Compared to conventional UT, PAUT offers higher probability of detection, faster scanning, and superior defect characterization.

When It Is Used

Pressure-vessel and pipeline girth-weld inspection
Corrosion mapping on tanks and vessels
Forging and casting inspection
Nozzle, T-K-Y joint, and complex-geometry inspection

Related Standards

ASME Section V Article 4 Mandatory Appendix VII and Article V, ASME Code Case 2235, AWS D1.1 Annex K, ISO 13588, ISO 23279.

Synonyms

Also called PA, PAUT, or Phased Array UT. Related advanced techniques include TFM and FMC.

How it works

A phased array probe carries many small piezoelectric elements in one housing. Firing them on individually calculated delays steers and focuses the beam electronically, so a single probe placed in one position can sweep a range of angles or march a focal spot through the thickness without the operator moving anything.

What it finds

Planar flaws in welds — lack of fusion, lack of penetration, cracking — with the sectorial scan showing where in the cross-section the reflector sits rather than only that something reflected. Corrosion mapping and thickness profiling benefit from the same positional record.

What it will not find

Flaws whose orientation presents no usable reflecting surface to any angle in the sweep still return little. Sweeping a range of angles widens the odds, it does not abolish the geometry: a tight, favourably-oriented crack in a coarse-grained austenitic weld can still hide. Near-surface resolution remains limited by the dead zone and the wedge, which is why a complementary surface method is usually specified alongside.

How it is actually done

Setup is where PAUT is won or lost: wedge selection, element count and aperture, focal law calculation, velocity and wedge-delay calibration, then sensitivity set on a block that represents the geometry and material being examined. Encoded scanning adds a position axis so the data can be re-examined later, which is the difference between an inspection you can defend and one you cannot.

Governing codes and standards

ASME Section V Article 4 with its mandatory appendices governs the technique in the ASME world; ISO 13588 covers PAUT of welds in the ISO world; ISO 19285 addresses acceptance for phased array weld testing. Acceptance criteria come from the referencing construction code, not from Article 4 itself.

Where it goes wrong

Treating the sectorial scan image as self-evident. The S-scan is a reconstruction built from the focal laws that were programmed; if the wedge delay or velocity is wrong, the image is confidently wrong in a way that looks entirely plausible. Verifying the setup on a block with known reflectors before the first weld is not optional.

Frequently asked questions

Is PAUT better than conventional UT?

It is better at coverage, at recording what it saw, and at examining geometry that would need several conventional probes. It is not a different physics — the same orientation limits and the same material attenuation apply. On a simple thickness check, conventional UT is faster and no less valid.

Does PAUT replace radiography?

For thick-section weld examination many codes now allow it as an alternative, and it detects planar flaws that radiography can miss. It does not produce the same kind of image, so where a specification demands a radiograph or an owner wants film-equivalent records, the substitution has to be agreed rather than assumed.

Where Phased Array Ultrasonic Testing fits in an inspection programme

A term is only useful when it connects to a decision. Phased Array Ultrasonic Testing appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.

Related terms

Ultrasonic Testing (UT) — Ultrasonic Testing (UT) is an NDT method that uses high-frequency sound waves (typically 0.5–25 MHz) to detect internal flaws and measure thickness in metals, plastics, and composites by analyzing reflected echoes from a transducer.
Time-of-Flight Diffraction (TOFD) — TOFD is an advanced UT technique using two angled probes in pitch-catch arrangement to detect and accurately size defects from the time of arrival of diffracted tip signals, achieving height-sizing accuracy of ±0.5 mm.
S-Scan (Sectorial Scan) — An S-scan is a phased-array ultrasonic image showing a fan of beams swept through a range of angles from a single probe position, displaying defect indications across the angular range in a single view.
L-Scan (Linear Scan) — An L-scan is a phased-array ultrasonic image produced by electronically stepping a fixed-angle beam along the array aperture, generating a side-by-side series of A-scans at constant angle and varying position.
Total Focusing Method (TFM) — TFM is an advanced ultrasonic imaging technique that post-processes Full Matrix Capture (FMC) data to synthetically focus the beam at every pixel in the region of interest, producing high-resolution images of complex defects.
Full Matrix Capture (FMC) — FMC is an ultrasonic data acquisition mode in which every element of a phased-array probe transmits in turn while all elements receive, producing a complete matrix of A-scans that can be post-processed using TFM and other algorithms.

More method terms

Radiographic Testing · Magnetic Particle Testing · Penetrant Testing · Eddy Current Testing · Visual Testing · Acoustic Emission Testing · Leak Testing · Thermography / Infrared Testing · Microwave Testing · Guided Wave Testing

Where this comes up in practice

Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.

Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.