Phased array ultrasonic testing equipment
PAUT Inspection: FMC, TFM and Equipment
A procurement-oriented explanation of phased array ultrasonic testing (PAUT), full matrix capture (FMC) and total focusing method (TFM), with the equipment and procedure boundaries kept beside the output.
Terminology
Separate acquisition from reconstruction.
PAUT, FMC and TFM describe related but different parts of an ultrasonic workflow. Treating them as interchangeable makes equipment comparisons unreliable because two systems may display similar images while retaining different raw data or using different acoustic paths.
PAUT controls multiple elements
A phased array probe contains multiple elements. By controlling when elements transmit and receive, a configured system can create linear scans, sector scans or other focal-law patterns. Beam coverage is not automatic: it depends on the active aperture, frequency, wedge, sound velocity, refracted angle, component geometry and expected discontinuity orientation.
FMC is a data-acquisition pattern
In a full matrix capture sequence, array elements are used across transmitter–receiver combinations to retain a larger set of A-scans for later processing. For a 64-element matrix, the complete square contains 64 × 64 = 4,096 transmit–receive A-scans. That arithmetic says nothing by itself about signal quality, coverage or probability of detection.
TFM reconstructs a region
Total focusing method applies time-of-flight calculations to the acquired data and reconstructs pixels over a selected region. ISO 23865:2021 provides general provisions for array-based FMC/TFM and related technologies, including manufacturing and in-service use, but it does not provide acceptance levels for discontinuities.
Procurement translation
Ask separately for active elements, parallel hardware channels, supported acquisition modes, retained raw data, TFM modes, reconstruction region, pixel size, refresh-rate conditions and export format. “3D capable” is not a complete technical specification.
Workflow comparison
Choose the smallest method that answers the question.
More data is useful only when the inspection procedure can convert it into a defensible decision. The following comparison is conditional; it does not rank every implementation or imply that one acquisition mode always produces better detection.
| Approach | Acquisition | Typical output | Useful when | Key constraints |
|---|---|---|---|---|
| Single-element UT | One probe element and configured sound path | A-scan and position-dependent records | A qualified, focused procedure answers a defined thickness or flaw question | Manual positioning, coverage, orientation, coupling and interpretation |
| Conventional PAUT | Multiple elements under configured focal laws | Sector, linear and encoded views | Steered or focused coverage improves access to the defined inspection volume | Focal-law design, wedge, aperture, angle range and scan plan |
| FMC with TFM | Matrix or related array dataset reconstructed after capture | Focused 2D or 3D image plus retained matrix data, where supported | Multiple acoustic paths and post-processing support the approved procedure | Data volume, processing, model accuracy, region, grid and material assumptions |
The UK Health and Safety Executive’s inspection and NDT guidance makes the broader control point explicit: the technique must be tailored to the damage sought, applied under a procedure and documented so that capability and repeatability can be assessed.
Application fit
Wind-turbine bolts need a defined sound path.
Bolt geometry can make flaw orientation and access more important than the instrument headline. Thread roots, shank transitions, the far end, probe contact area and bolt length all affect the usable acoustic paths. Specify whether the task is crack-like indication detection, sizing, preload or stress measurement, or a combination.
A 2024 University of Strathclyde research study of wind-turbine bolted connections evaluated PAUT for stress measurement and defect detection. Its M42 blind test was a research result under a specific setup; the authors also state that material-specific acoustoelastic calibration and temperature effects need further control. It should not be converted into a universal field-accuracy claim.
A Sonatest application note reports encoded PAUT scans on two turbine-bolt specimens with induced cracks and notches. The note documents the probe, scanner, couplant, angles and specimens—useful detail for method planning—but a two-specimen demonstration is not a general probability-of-detection study.
- 01Define the target
State flaw type, orientation, minimum relevant size, region and acceptance basis before selecting a probe.
- 02Model the sound path
Use bolt geometry, material velocity, threads and available contact face to design coverage and identify dead zones.
- 03Qualify the setup
Use representative reference features or specimens, controlled coupling and a documented calibration sequence.
- 04Retain the record
Store raw data, setup file, scan position, calibration, analyst result and review state separately.
Qualification boundary
Instrument channel count, imaging speed or a vendor demonstration cannot establish inspection capability alone. Require a component-specific probe, sound-path model, representative reference feature, calibration sequence, scan plan, personnel requirements and acceptance basis.
Buyer checklist
Specify the equipment as a complete chain.
A phased array ultrasonic testing machine is only one part of the inspection configuration. The proposal should connect component, probe, scanner, acquisition, reconstruction, calibration, personnel, procedure and deliverable. Missing one of those links makes two equipment quotations difficult to compare.
Hardware and acquisition
- Parallel hardware channels, active element count and supported probe connectors
- Pulser voltage, bandwidth, digitisation, sample depth and data-throughput limits
- FMC, conventional PAUT, encoded scanning and offline-processing support
- Scanner, encoder, wedge or probe holder matched to the component geometry
TFM processing and evidence
- Supported wave modes, reconstruction region, pixel resolution and refresh-rate test conditions
- Whether full matrix data, setup files, processed images and annotations are all retained
- Online and offline review behaviour, traceable reprocessing and export format
- How calibration changes, analyst decisions and report revisions are logged
Procedure and acceptance
- Applicable code, owner specification or engineering procedure
- Reference specimen, sensitivity, coverage demonstration and known limitations
- Personnel qualification, job-specific training and independent review requirements
- Acceptance criteria kept separate from the equipment's ability to display an indication
Use the configuration input checklist to structure the asset, access, environment, evidence and integration details before requesting a quotation.
Evidence register
Sources and limitations
Primary, official and clearly identified supplier sources support this method explanation. The supplier application note is treated as a limited demonstration, not independent validation.
- ISO 23865:2021 — official scope for general use of FMC/TFM and related technologies; it does not provide discontinuity acceptance levels.
- Heliyon (2024), University of Strathclyde repository — primary study of PAUT stress measurement and defect detection in wind-turbine bolted connections.
- Sonatest wind-turbine bolt application note — supplier-documented trial setup on two induced-defect specimens.
- UK HSE inspection/NDT guidance — official guidance on procedure, capability, coupling, records and personnel controls.
Limitation: the cited sources do not establish capability for an unspecified instrument or field configuration. Detection, sizing, stress measurement and inspection time cannot be generalised across probes, materials, geometries, procedures or acceptance standards.
See the source and editorial policy for how supplied product manuals, external method sources and claim limitations are kept separate.
Decision support
Frequently asked questions
What is phased array ultrasonic testing?
Phased array ultrasonic testing uses multiple transducer elements with controlled timing to create and receive ultrasonic beams. Depending on the configured focal laws and acquisition mode, the system can steer, focus or reconstruct sound paths. The probe, wedge, material, geometry, calibration and procedure determine what the resulting data can support.
Are FMC and TFM the same thing?
No. Full matrix capture is an acquisition method that records transmitter–receiver combinations across an array. Total focusing method is a reconstruction algorithm that uses an FMC or related dataset to calculate an image over a defined region. Acquisition quality and the selected reconstruction parameters remain separate control points.
Does a TFM image prove that a component is acceptable?
No. An image must be interpreted under an approved procedure with calibrated equipment, known geometry, qualified personnel and applicable acceptance criteria. ISO 23865 gives general provisions for FMC/TFM but explicitly does not establish acceptance levels for discontinuities.
Can one PAUT probe inspect every wind-turbine bolt?
No. Bolt diameter, length, head and thread geometry, material, attenuation, expected flaw orientation and available contact surface affect probe and scanner selection. A representative reference feature, coverage plan and qualified procedure are required for the specific configuration.
Engineering review
Match the array, data path and procedure to the component.
Provide the component geometry, material, expected flaw orientation, access surface, inspection standard and required output. We’ll identify the configuration questions for technical review.