Ultrasonic Testing (UT) is a non-destructive testing (NDT) method that uses high-frequency sound waves to detect internal flaws, measure material thickness, and assess weld integrity in metals, plastics, and composites.
How Ultrasonic Testing Works
- Pulse-Echo Principle
– A transducer sends ultrasonic waves (0.5–25 MHz) into the material.
– Sound waves reflect off defects or boundaries and return to the transducer.
– The time of flight and amplitude of echoes determine flaw location and size.
- Display Modes
– A-Scan (Amplitude vs. Time) – Basic flaw detection & thickness measurement.
– B-Scan (Cross-sectional view) – Shows depth and length of defects.
– C-Scan (2D Top View) – Color-mapped defect imaging (used in aerospace).
- Couplant Required
– A gel or liquid (water, oil) ensures sound transmission into the material.
Advantages of UT
Detects subsurface flaws (unlike visual or dye penetrant).
Highly accurate (measures defect depth & size precisely).
No radiation hazard (safer than radiography).
Works on most materials (metals, plastics, ceramics).
Limitations of UT
Surface must be smooth (rough surfaces scatter signals).
Limited for coarse-grained materials (e.g., cast iron, austenitic welds).
Requires skilled technicians (data interpretation is complex).
Applications of Ultrasonic Testing
– Weld inspection (cracks, lack of fusion, porosity).
– Corrosion mapping (pipeline & tank thickness measurement).
– Aerospace & automotive (composite bonding defects).
– Rail & power plants (crack detection in rails & turbines).
Standards for Ultrasonic Testing
– ASTM E317 (Standard Practice for UT)
– ASME BPVC Section V (Boiler & Pressure Vessel Code)
– ISO 17640 (UT of Welds)
– API 5UE (Ultrasonic Evaluation of Pipeline Girth Welds)
When to Use Ultrasonic Testing?
– For internal flaw detection (cracks, voids, inclusions).
– When thickness measurement is critical (corrosion assessment).
– For high-value components (aircraft, nuclear reactors).
