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What Is PAUT? A Comprehensive Guide to Phased Array Ultrasonic Testing
PAUT (Phased Array Ultrasonic Testing) is the evolution of conventional single-element UT. Using a multi-element array probe, it electronically steers and focuses the ultrasonic beam — enabling wide-area coverage and multi-angle imaging in a single scan.
How Does PAUT Work?
Conventional UT sends a single ultrasonic pulse. PAUT uses a probe with 16 to 256 elements. Applying small time delays (phase shifts) to each element steers the beam to a desired angle and focuses it at a chosen depth.
This enables:
- Sectorial scan (S-scan): Simultaneous imaging across a defined angle range
- Electronic scan (E-scan): Lateral scanning by activating different element groups while the probe remains stationary
- Compound scan: Both modes combined for maximum coverage
A-scan, B-scan, C-scan, and S-scan images are all produced in a single pass — increasing both scan speed and data richness.
What Is TOFD (Time of Flight Diffraction)?
TOFD is a separate ultrasonic technique frequently combined with PAUT. It is based on diffraction rather than reflection:
- A transmitter sends a pulse that diffracts from the tip of a discontinuity
- A receiver detects the diffracted wave
- The time of flight is measured to precisely determine the position and height of the discontinuity
TOFD provides superior accuracy for sizing weld discontinuities — particularly height measurement — compared to conventional methods. It is commonly specified in Risk-Based Inspection (RBI) programmes and for critical pipelines and pressure vessels.
Conventional UT vs PAUT
| Feature | Conventional UT | PAUT | |---------|----------------|------| | Probes | Separate probe per angle | Single probe, multiple angles | | Scan speed | Slow (re-setup per angle) | Fast (electronic steering) | | Imaging | A-scan only | A, B, C, S-scan | | Operator skill requirement | High | High | | Discontinuity sizing | Limited | High accuracy | | Equipment cost | Low | High | | Documentation | Manual | Automatic digital record |
When PAUT Has the Edge
Complex geometries: PAUT's electronic steering is effective at weld roots, heat-affected zones (HAZ), and nozzle welds where standard angles are insufficient.
Speed-critical inspections: On large-area pipeline or tank shell surveys, conventional UT manual scanning takes significantly longer than PAUT electronic scanning.
Documentation requirements: PAUT scans automatically generate digital records. Combined with TOFD data, they produce a comprehensive inspection file that meets the recording level required by RBI programmes.
Discontinuity sizing: PAUT is significantly more accurate than conventional UT for measuring the depth and height of fatigue cracks, weld discontinuities, or corrosion areas.
Applicable Standards
- EN ISO 13588: General standard for PAUT
- ASTM E2700: PAUT for weld inspection
- ASME Sec. V Art. 4: Pressure vessel applications
- ASTM E2373: TOFD technique
- EN ISO 10863: TOFD application on welds
Common Applications
- Pipelines and piping: Accurate scanning even on thin-wall components
- Pressure vessels and boilers: Weld, nozzle, and shell inspection
- Petrochemical plants: Subsurface crack detection and wall thickness profiling
- Aerospace: Interlaminar separation in composite and metallic components
- Energy sector: Turbine components, boiler tubes
- Structural steel: Bridge and frame welds
Software Infrastructure for NDT Companies
PAUT and TOFD inspections generate large data files. Correlating this data with inspection reports, matching it to correct personnel qualifications, and making it quickly accessible for audit preparation are all critical.
ceres-ndt supports PAUT and TOFD work orders: equipment calibration records, technician certifications (EN ISO 9712 Level II/III), and report archives are held on a single platform.
Digitalise your PAUT/TOFD work orders, reports, and archives with ceres-ndt. Contact us for a demo.
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