Phased Array Ultrasonic Testing (PAUT)

Phased Array Ultrasonic Testing (PAUT) is an advanced non-destructive testing (NDT) method that uses multiple ultrasonic elements and electronic time delays to steer, focus, and scan sound beams. It provides detailed imaging of internal structures and is widely used for weld inspection, corrosion mapping, and flaw characterization.

Overview

Unlike conventional UT, which uses a single probe and fixed beam, PAUT employs an array of small ultrasonic transducers. By controlling the timing of pulses sent to each element, the beam can be electronically steered and focused at different angles and depths. This allows rapid scanning, improved coverage, and high-resolution imaging of flaws.

Apparatus and Working

Apparatus

  • Phased array probe: Contains multiple piezoelectric elements arranged in a line or matrix.
  • PAUT instrument: Generates pulsed signals, controls phasing, and displays results.
  • Couplant: Gel, oil, or water to transmit sound waves efficiently.
  • Calibration blocks: Reference standards with known reflectors for setup and accuracy.
  • Data acquisition software: For imaging, recording, and analysis.

Working Steps

  1. Surface preparation: Clean the surface and apply couplant.
  2. Probe placement: Position the phased array probe on the test surface.
  3. Beam steering: Electronic time delays steer and focus the ultrasonic beam.
  4. Scanning: The probe sweeps across the weld or component, capturing multiple angles.
  5. Imaging: Signals are processed into cross-sectional images (sectorial scans, B-scans, C-scans).
  6. Interpretation: Inspectors analyze images to locate, size, and characterize flaws.

Principle

PAUT is based on the principle of constructive and destructive interference of ultrasonic waves. By applying controlled time delays to each element in the probe, the wavefronts combine to form a focused beam at a desired angle and depth. This electronic beam steering allows rapid inspection without physically moving the probe, producing detailed images of internal structures.

Advantages and Disadvantages

Advantages

  • Provides high-resolution images of flaws and weld profiles.
  • Electronic beam steering reduces mechanical probe movement.
  • Capable of inspecting complex geometries and thick materials.
  • Data can be stored, replayed, and analyzed later.
  • Improved probability of detection compared to conventional UT.

Disadvantages

  • Equipment is more expensive than conventional UT.
  • Requires skilled operators and advanced training.
  • Setup and calibration are more complex.
  • Large data files require proper storage and management.

Applications

  • Weld inspection: Detecting cracks, lack of fusion, porosity, and incomplete penetration.
  • Corrosion mapping: Measuring wall thinning in pipelines and vessels.
  • Aerospace: Inspection of composite structures and turbine components.
  • Power generation: Examination of pressure vessels, steam lines, and nuclear components.
  • Structural engineering: Testing bridges, cranes, and heavy machinery parts.

Welding Defects Detectable by PAUT

  • Lack of fusion: Areas where weld metal has not bonded with base metal or adjacent passes.
  • Incomplete penetration: Root defects extending through thickness.
  • Cracks: Longitudinal, transverse, or crater cracks inside welds.
  • Slag inclusions: Non-metallic inclusions trapped in weld metal.
  • Porosity clusters: Gas pockets inside welds, visible as grouped indications.
  • Lamination and lack of bonding: Planar defects in base material or fusion line.