Electromagnetic induction infrared thermography for steel pipe defect detection

Principle and equipment parameters

The paper uses high frequency electromagnetic induction as a thermal excitation source and records the resulting surface temperature field with an infrared camera.

The reported camera frame frequency is 128 Hz and the thermal sensitivity is 0.08 K, which is sufficient to capture transient thermal anomalies associated with pipe defects.

Item	Reported feature	Practical significance
Excitation method	Electromagnetic induction heating	Provides localized heating without direct contact
Camera frame rate	128 Hz	Captures fast thermal responses in small components
Thermal sensitivity	0.08 K	Improves detection of shallow thermal anomalies
Detected defect types	Inner wall volume type and outer surface planar type	Demonstrates sensitivity to different defect geometries

The method is attractive for pipe inspection because induction heating can produce a strong thermal contrast near flaws, and infrared imaging can then convert that contrast into a measurable surface temperature pattern.

Defect detectability and influencing factors

The detectability of a defect depends on heating uniformity, excitation duration, scan speed, defect depth, defect orientation, wall thickness, pipe diameter, surface emissivity, and ambient air movement.

For internal volume type defects, the thermal signature is weaker and more delayed than for external surface defects, so the timing window for image capture is critical.

Surface scale, paint, coating, and roughness can change emissivity and create false indications, so surface preparation and reference specimens are essential for reliable interpretation.

Implementation and verification

The method should be validated with known reference flaws before use in production, and inspection parameters should be documented in a written procedure.

For pipe work, infrared thermography is best treated as a complementary method to ultrasonic, radiographic, magnetic particle, or eddy current testing, especially when defect sizing is required.

Personnel qualification, camera calibration, data retention, and repeatability checks are necessary because the technique depends heavily on thermal transient interpretation.

In summary, the paper demonstrates that induction heated infrared thermography can be a practical screening method for steel pipe defects, but its reliability depends on controlled thermal excitation and disciplined inspection practice.