What are the five common probes used in ultrasonic testing?

Ultrasonic testing is a non-destructive testing method commonly used in various industries to inspect the integrity and detect defects in materials. This method utilizes high-frequency sound waves to penetrate the object being tested, gathering information about its internal structure or detecting any flaws present. One key component of ultrasonic testing is the use of probes, which emit and receive the sound waves. In this article, we will explore the five most common types of probes used in ultrasonic testing.

1. Contact Probes

Contact probes are the most basic and widely used type of probe in ultrasonic testing. As the name suggests, these probes require direct contact with the test material to transmit and receive sound waves. They consist of a transducer, which converts electrical energy into sound waves, and a wear-resistant contact face that is placed in contact with the material's surface. Contact probes are suitable for testing solid and relatively flat surfaces, providing high-resolution images and precise measurements.

2. Immersion Probes

Immersion probes, also known as immersion transducers, are designed for testing materials immersed in a liquid medium. These probes emit sound waves through the liquid, which then enter the test material. Immersion probes come in various configurations, including single-element and multi-element designs. They are particularly useful for inspecting large objects or complex shapes, where direct contact may not be feasible. Immersion probes provide excellent sensitivity and offer greater control over beam angles and focal points.

3. Phased Array Probes

Phased array probes utilize advanced technology to enhance the capabilities of ultrasonic testing. These probes consist of multiple small elements, each capable of transmitting and receiving sound waves independently. By controlling the timing and amplitude of these elements, the probe can create and steer focused beams in different directions. This allows for improved defect characterization, detection of smaller flaws, and the ability to test at various angles without physically moving the probe. Phased array probes provide flexibility and efficiency in testing complex geometries.

4. Time-of-Flight Diffraction (TOFD) Probes

TOFD probes are specifically designed for detecting and sizing planar defects, such as cracks, in welds. These probes utilize two separate transducers arranged on opposite sides of the weld joint. One transducer emits an ultrasonic pulse, while the other receives diffracted waves from the edges of any defects present. By analyzing the time taken for the diffracted waves to reach the receiver, TOFD probes can accurately measure the height and length of defects. This technique offers high accuracy, speed, and can provide full coverage of the inspected area.

5. Dual Element Probes

Dual element probes are commonly used in applications that require higher penetration and sensitivity for detecting defects near the surface or within highly attenuative materials. These probes consist of two separate elements within a single housing. One element emits sound waves, while the other separately receives the echo from the back wall or any discontinuities in the material. The separation of transmit and receive functions allows for better resolution and signal-to-noise ratio, enabling the detection of subtle defects that may go undetected with other probe types.