PRINCIPLE
Surface Eddy Current test of bolt holes
Eddy current testing is a NDT method based on the principle of electromagnetic induction. Alternating current is passed through a coil placed next to the test piece. The coil produces an alternating magnetic field called the primary magnetic field. In response, eddy currents are produced in a material that oppose the primary magnetic field. The magnetic field produced by the eddy current interact with the primary field and affects the impedance of the coil. This change in impedance is measured and displayed by the instrument and is the basis of eddy current testing. Eddy current testing is applicable only to conductive materials.
EQUIPMENT
Eddy current machine. Pencil and spot probes for surface inspection. Bobbin and encircling probes for tubing inspection. Calibration blocks with EDM notches for surface notches. Calibration tube with hole and flat bottom holes for tubing inspections.
Figure. Principle of Eddy Current testing. A crack disrupts eddy current field can results in coil change in impedance from 1 to 2
APPLICATIONS
The two main types of tests are surface ECT and heat exchanger tubing ECT . Surface eddy current testing is widely used in the aerospace industry for inspection of airframe structures and bolt hole inspections. Tubing inspection is widely used in the nuclear and petrochemical industry for inspection of heat exchanger tubing.
ECT TRAINING
SNT-TC-1A Level I Duration – 40 hours
SNT-TC-1A Level II Duration – 40 hours after completion if Level I
NAS410 Level I Duration – 40 hours
NAS410 Level II Duration – 40 hours after completion if Level I
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