Non-Destructive Testing Technology for Shallow Subsurface Defects in Rails: A Review with Focus on Ultrasonic Surface...

Area of Science:

• Materials Science
• Mechanical Engineering
• Non-Destructive Testing

Background:

• Increasing rail traffic necessitates reliable detection of shallow subsurface rail damage.
• Defects in the upper 0.5-10 mm of rails pose significant operational safety risks.

Purpose of the Study:

• To critically review non-destructive testing (NDT) technologies for shallow subsurface rail defects.
• To evaluate ultrasonic surface-wave excitation routes and compare their laboratory capabilities with field evidence.

Main Methods:

• Review of magnetic flux leakage, magnetic particle inspection, visual inspection, eddy current testing, and conventional ultrasonic testing.
• Focus on four ultrasonic surface-wave routes: contact piezoelectric, active air-coupled, electromagnetic acoustic (EMAT), and laser ultrasonic.
• Development of an engineering decision matrix linking defect characteristics and inspection conditions to a workflow.

Main Results:

• Contact piezoelectric UT/PAUT identified as the most mature quantitative confirmation route for shallow rail defects.
• EMAT, air-coupled UT, and laser UT show method-specific advantages but require more validation.
• Source-conditioned evidence reported due to variations in studies (defect geometry, rail conditions, etc.).

Conclusions:

• Contact piezoelectric UT/PAUT is the leading technology for quantitative confirmation of shallow rail damage.
• Further in-service validation is needed for EMAT, air-coupled UT, and laser UT to realize their potential.
• An engineering decision matrix aids in selecting appropriate NDT methods for rail integrity assessment.