Page 252 - CITS - Welder - Trade Theory

WELDER - CITS

The first one is a high-frequency instrument for detecting surface-breaking cracks in non-ferrous and ferrous
components.
The second one is a low-frequency instrument for inspecting subsurface cracks in non-ferrous components.

In ferrous materials, identifying the subsurface cracks is possible only when the materials are saturated
magnetically to eliminate permeability impacts.
This is a complicated procedure that is achievable with automated tube testing systems. Applications of Eddy
Current Testing are widely used in detection.
In the detection procedure of surface cracks, eddy currents are too sensitive. High frequencies of the order of 2
MHz provide high resolution, but the probes are too small, and covering a vast surface area consumes a lot of
time.
Large probes are required for low-frequency crack detectors in order to enable favorable coil inductances.

The setting of the frequency is critical, and it is in the range of 10 Hz to 100 Hz, which depends on the depth of
penetration needed.
Phase sensing circuits are necessary because phase changes, rather than amplitude changes, have a significant
impact on the subsurface eddy current fields.
4 Measurement of The Coating Thickness
The outstanding surface resolution of Eddy current testing makes it highly useful.
Its application is seen in meticulously measuring the thickness of the coatings, whether metallic or paint, on the
components.

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CITS : C G & M - Welder - Lesson 83 - 97