Eddy current testing a modern Non-destructive
testing – NDT method that has become one of the prime tool for quality control
of products, materials and structures at various stages of manufacturing and
in-service inspections. Eddy current inspection can be used to find finest
surface and subsurface flaws in any conductive material. Spectrums of quality
control engineering applications are existing applying Eddy current principles.
Present Eddy current NDT method has applications in Aerospace Component Inspections,
Heat exchanger tube inspections and other critical engineering applications.
1. Material
sorting – mix up of various grade of materials either chemically different or
variation in mechanical properties or metallurgically difference
in structures can sorted using Eddy current testing equipments.
2. Surface
and subsurface flaw detection in conducting materials. Flaws could be cracks,
laminations, and other discontinuities that can be detrimental to the product
performance.
3. Conductivity
testing for metals.
4. Accurate
measurement of Coating thickness with Eddy current testing. The coating can be
conductive or nonconductive with few limitations on the accuracy of the
measurements.
5. This NDT
inspection method can also be used for thickness testing and measurement of
especially low thicknesses of conductive materials where there is a restriction
on using Ultrasonic thickness gauging due to component configuration or the
quantum of inspection. Eddy current inspections can be either contact or
non-contact type tests.
6. Eddy
current testing is an effective means of verification of integrity of
structures and estimation of corrosion damages for heat exchanger tubes.
Routine in-service maintenance inspectionsusing Eddy
current techniques yield reliable data for analysis and condition monitoring of
plants and structures.
When a test specimen is brought into proximity
to the alternating flux field of an eddy current coil, coil flux causes
electrons in the specimen to circulate in a swirling eddy-like pattern; hence
the term “eddy currents.”Eddy current behavior depends on the properties of both the flux
and the specimen itself. So eddy currents are circular alternating currents
caused by a varying magnetic field.
● Eddy
currents are Sensitive to small cracks and other defects
● Eddy
current testing detects surface and near surface defects
● Eddy
current Inspection gives immediate results
● ET
Equipment is very portable
● This
Method can be used for much more than flaw detection
● Minimum
part preparation is required
● Eddy
current Test probe does not need to contact the part
● Eddy
currents Inspects complex shapes and sizes of conductive materials
● Eddy
current inspection is suitable for only conductive materials
● Surface
must be accessible to the Eddy current probe/s
● Skill and
training required to carry out eddy current inspection is more extensive than
other techniques
● Surface
finish and roughness may interfere with test results
● Reference
standards needed for setup for every application
● Depth of
penetration is limited
● Flaws such
as de-laminations that lie parallel to the probe coil winding and probe scan
direction are undetectable and may get detected only using specially designed
Eddy current probes for such applications.