Please enable JavaScript.
Coggle requires JavaScript to display documents.
EDDY CURRENT TESTING METHOD (REFERENCE STANDARD (Set 5 Standards…
EDDY CURRENT TESTING METHOD
EQUIPMENT
Portable Eddy Current Flaw Detector
Probes
Pencil Probes
Explaination
Depends on surface condition
Used for surface crack detection
Smaller diameter probes for high frequency and high resolution
Surface Probes
Explaination
Larger diameter
Lower frequencies for deeper penetration
Used for corrosion detection
Identifying flaws
Sorting Blocks
REFERENCE STANDARD
Conductivity standards
Flat plate discontinuity standards
Flat plate metal thinning standards
Tube discontinuity standards
Tube metal thinning standards
Hole discontinuity standards
CALIBRATION
Reasons
To ensure readings are consistent
To determine the accuracy
To establish the reliability
PRODUCING EDDY CURRENT
Following the principle of electromagnetism
The eddy current also produce magnetic field that will oppose primary magnetic field base on Lenz's Law
The eddy current will be produce on the surface of the conductor and it will form circular electric field
The conductive material will induced the magnetic field that is produce by the coil
The conductive material will put under the coil
Flow AC current through the coil in order to produce varying magnetic field
Required magnetic field and a piece of conductor
TESTING
Defect Detection
The defect that is parallel to the eddy current field cannot be detected
The changes can be observe using galvanometer or any other device
The disturb eddy current will become feedback of the primary current which is coil
The eddy current will disturb when there is defect
It only detect surface and near surface of the test material
Higher frequency gives better sensitivity but low penetration
Frequency choose is high
Thickness Measure
The strongest density is at surface of the test material
The eddy current density decrease exponentially with the depth travel
Lower frequency gives better penetration depth
The phenomenon is called skin effect
Lower frequency is choose
The eddy current density will decrease for about 1/e, or about 37% of the surface density
This is called the standard depth of penetration (δ)
The depth of the penetration can be changes using different frequency
APPLICATION
Aerospace Industries
Petrochemical Industries
REASONS
Surface and tubing inspections
Used extensively in aerospace and petrochemical industries
Very sensitive in detecting crack
Can be performed both on ferromagnetic materials
