Core Principles of Probe Selection

The design of the bi-crystal longitudinal wave probe with independent transmitter and receiver wafers effectively eliminates the near-field blind spot and enhances the detection sensitivity, which is especially suitable for non-destructive testing of thin-walled parts, coarse-grained materials and complex structures. The selection of core parameters should follow the following logic:

1.Frequency matched to the grain diameter

Normal material(e.g. carbon steel, aluminum):We preferred to balance sensitivity and penetration.For example, a 5Mhz probe can be used to meet the AA sensitivity requirements.

Coarse grain materials(such as austenitic stainless steel): Lower frequency 1-2Mhz will be more proper for this kind of material, it can minimize the acoustic scattering interference and improve signal-to-noise ratio.

2.Focal distance matched to the thickness

The focal point of the beam should be at the center of the measured wall thickness, typically in the range of 15-50mm. e.g. for pipes with wall thicknesses of 8-20mm, a focal length of 20-30mm is recommended to ensure that the defect signal is maximized.

Smaller wafers (e.g. 6 x 6 mm) are used for curved parts to enhance coupling and minimize edge distortion.

3.The refractive angle sweep covers the defects

General weld inspection: Combinations of 45°-70° refractive angles (e.g. 45°+60°) cover most defect directions. For example, a pressure vessel with a wall thickness of more than 50 mm requires a full cross-section sweep with a combination of 45° and 60° probes.

Near-surface defects: The 70° probe can be used to detect surface and sub-surface cracks with a small near-field area.

Typical Applications and Industrial Specifications

Automobile Manufacturing Industry

Application Scenario:

Internal defect detection of thin-walled castings such as engine blocks and wheel hubs.

Body welding joint quality assessment, such as aluminum alloy spot welding melt core size determination.

Specification selection:

High-frequency probe (5-10MHz) with small wafer (6×8mm) to enhance near-surface resolution. For example, when inspecting aluminum alloy parts 4-8mm thick, the 5MHz probe can clearly identify defects up to 0.5mm.

Curved parts require custom curved delay blocks to ensure that the sound beam is directed perpendicularly to the inside of the surface.

Aerospace Industry

Application Scenario

Delamination and debonding detection of composite structures (e.g. carbon fiber wings).

Near-surface crack screening of precision components such as turbine blades.

Specification Options:

Phased array dual crystal probes (e.g. 10MHz linear array), combined with multi-angle beam deflection technology, to achieve full coverage detection of complex structures.

High-temperature environments (e.g., engine components) require the use of delay block materials with a temperature resistance of >200°C, in conjunction with low-frequency (2.25MHz) probes to penetrate thick-walled components.

Petrochemical Industry

Application Scenario:

Weld and corrosion defect detection of pressure vessels and oil pipelines.

Delamination defect screening for thick-walled austenitic stainless steel equipment.

Specification options:

Combination of longitudinal wave oblique probes (refraction angle 45°-70°) to cover defects in different directions. For example, a 70° probe is recommended for welds with a wall thickness of 14-25 mm, and for >50 mm a combination of 45° and 60° is required.

Coarse crystalline materials (e.g. cast steel valves) require a 1.5MHz probe with a wide bandwidth design to improve signal-to-noise ratio.