1. The principles of Ultrasonic Inspection:

The sound waves travel through the material with some attendant loss of energy (attenuation) and are reflected at interfaces. The reflected beam is displayed and then analyzed to define the presence and location of flaws or discontinuities.

High-frequency sound wave are transmitted into a material to detect imperfections or to locate changes in material properties. Cracks, laminations, shrinkage cavities, bursts, flakes, pores, disbonds, and other discontinuities that produce reflective interfaces can be easily detected. Inclusions and other inhomogeneities can also be detected by causing partial reflection or scattering of the ultrasonic waves or by producing some other detectable effect on the ultrasonic waves.

Picture 1: The principles of Ultrasonic Inspection.

2. The process of Ultrasonic Inspection:

- Pulse-echo technique: ultrasonic probe introduces sound pulses into a test component; internal imperfections or geometrical surfaces return reflections (echoes) to the probe.

- Returned pulses are displayed on the screen (the  so-called A-Scan).

- Distance from the probe to reflector and size of the reflector (flaw inside the material) can be determined.

Picture 2: Imspection with UT.

Picture 3: Equipment in UT.

3. Advantages and Disadvantages of UT:

- Advantages:

• Sensitive to cracks at various orientations.
• Portability.
• Nonhazardous to operations and safety.
• Able to penetrate thick sections.
• Measures depth and through wall extent.

- Disadvantages:

• No permanent record (unless automated).
• Not easily applied to complex geometries and rough surfaces.
• Unsuited to course grained materials.
• Requires highly skilled and experienced technicians.