This document discusses eddy current testing, a non-destructive testing method. It uses an alternating current in an excitation coil to generate an eddy current in the test material. Variations in the eddy current caused by flaws are detected and analyzed. Advantages include fast scanning, no couplant needed, and ability to inspect through coatings. Limitations include requirement for conductive materials and limited depth of penetration. Applications include surface crack detection and material sorting.

1. M.KARTHIKEYAN
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEERING & TECHNOLOGY, SIVAKASI
karthikeyan@aaacet.ac.in
OML751 TESTING OF MATERIALS

2. UNIT III NON DESTRUCTIVE TESTING
1. Visual inspection
2. Liquid penetrant test
3. Magnetic particle test
4. Thermography test
5. Radiographic test
6. Eddy current test
7. Ultrasonic test
8. Acoustic emission
Principles, Techniques, Methods, Advantages and Limitations,
Applications.

3. EDDY CURRENT TESTING
Ac current
Magnetic field
Specimen
Eddy current
Eddy current’s magnetic field

4. • Eddy current testing uses the principle of electromagnetic
induction to detect flaws in conductive materials.
• An excitation coil carrying current is placed in proximity to the
component to be inspected.
• The coil generates a changing magnetic field using an
alternating current, which interacts with the component
generating eddy currents.
• Variations in the phase and magnitude of these currents are
monitored either by using a second coil, or by measuring
changes to the current flowing in the excitation coil.
• The presence of any flaw will cause a change in the eddy current
field and a corresponding change in the phase and amplitude of
the measured signal.
• In the case of nondestructive testing (NDT), these are displayed
on an eddy current flaw detector as a distinct change in signal

5. ADVANTAGES
• Provides a faster scanning speed than conventional ultrasonic
testing (UT)
• Unlike UT, requires no fluid couplant
• The surfaces need minimal preparation
• Eddy current testing can be used through several millimeters of
coating
• Can detect very small cracks in or near the surface of the
material
• Physically complex geometries can be investigated
• The testing devices are portable
• Provide immediate feedback
• The probe does not necessarily have to be in contact with the
test object

6. LIMITATIONS
• Only conductive materials can be inspected
• Surface must be accessible to the probe
• Skill and training required is more extensive than other
techniques
• Surface finish and and roughness may interfere
• Reference standards needed for setup
• Depth of penetration is limited
• Flaws such as delaminations that lie parallel to the probe
coil winding and probe scan direction are undetectable

7. APPLICATIONS
 Eddy current testing can be used for a wide range of
applications.
 It is often applied for surface crack detection and material
sorting.
 Material sorting is used to ensure that the proper materials are
in use and to verify component materials or assembly features
(such as the orientation or position of a subcomponent in an
assembly).