Eddy Current Testing (ET)

Eddy current Testing is based on the principle that a coil in air with alternating current flowing through it has unique and measurable resistive and inductive reactance components of it’s electrical impedance. Eddy currents are induced when an electrically conductive test object is placed close to the coil. Mutual induction occurs and both components of the circuit impedance are changed by a given amount. This change is based on frequency of AC used, proximity between probe coil and test part, dimensions of the test part, it’s conductivity, permeability and the presence of flaws or discontinuities. *Indicates the minimum days of classes.

Training to Level I Duration: 8 days*
Training to Level II Duration: 10 days
Training – Level II Refresher Duration: 8 days
  • View Syllabus

    1.0 Introduction to Electromagnetic testing

    1.1 Eddy current / Flux leakage
    1.2 Brief history of testing
    1.3 Basic principles of testing

    2.0 Electromagnetic theory

    2.1 Eddy current theory
    2.2 Generation of eddy currents by means of an alternating current field
    2.3 Effect of fields created by eddy currents ( impedance changes)
    2.4 Effect of change of impedance on instrumentation
    2.5 Properties of eddy current
    2.6 Travel in circular direction
    2.7 Strongest on surface of test material
    2.8 Zero value at center of solid conductor placed in an alternating magnetic field
    2.9 Strength, time relationship and orientation as functions of test system
    2.10 Have properties of compressible fluids
    2.11 Small magnitude of current flow
    2.12 Relationship of frequency and plane with current in coil
    2.13 Effective permeability variations
    2.14 Effect of discontinuity orientation
    2.15 Power losses

    3.0 Flux leakage theory

    3.1 Terminology and units
    3.2 Principles of magnetization
    3.3 BH curve
    3.4 Magnetic properties
    3.5 Magnetic field
    3.6 Hysteresis loop
    3.7 Magnetic permeability
    3.8 Factors affecting permeability

    4.0 Magnetization B electromagnetism theory

    4.1 Oersted’s law
    4.2 Faraday’s law
    4.3 Electromagnetic

    5.0 Flux leakage theory and principle

    5.1 Residual
    5.2 Active
    5.3 Tangential leakage
    5.4 Normal leakage fields

    6.0 Readout mechanism

    6.1 Calibrated or uncalibrated meter
    6.2 Null meter with dial indicator
    6.3 Oscilloscope and other monitor displays
    6.4 Alarm, lights etc.
    6.5 Numerical counters
    6.6 Marking system
    6.7 Sorting gates and tables
    6.8 Cutoff saw or shears
    6.9 Automation and feedback
    6.10 Strip chart recorder

    7.0 Eddy current sensing elements

    7.1 Probes
    7.2 Absolute
    7.3 Differential
    7.4 Lift off
    7.5 Theory of operation
    7.6 Applications
    7.7 Advantages
    7.8 Limitations

    8.0 Through, encircling or annular coils

    8.1 Absolute
    8.2 Differential

    9.0 Fill factor

    9.1 Theory of operation
    9.2 Applications
    9.3 Advantages
    9.4 Limitations

    10.0 Factors affecting choice of sensing elements

    10.1 Type of part to be inspected
    10.2 Type of discontinuity to be inspected
    10.3 Speed of testing required
    10.4 Amount of testing required
    10.5 Probable location of discontinuity

    11.0 Comparison of techniques

    11.1 Thickness gaging
    11.2 Sorting
    11.3 Conductivity
    11.4 Surface or subsurface flaw detection
    11.5 Tubing
    11.6 Remote field

    12.0 Practical workout

    12.1 Using a Hocking Phasec instrument
    12.2 Testing of a variety of components manually
    12.3 Automation
    12.4 Recording or storage of signals

    13.0 Indications, discontinuities and defects

    13.1 Indications
    13.2 Discontinuities
    13.3 Inherent
    13.4 Processing
    13.4 Service

    14.0 Manufacturing processes and associated discontinuities

    14.1 Casting processes and associated discontinuities
    14.2 Ingots, blooms and billets
    14.3 Sand casting
    14.4 Centrifugal casting
    14.5 Investment casting

    15.0 Wrought processes and associated discontinuities

    15.1 Forgings
    15.2 Rolled products
    15.3 Extruded products

    16.0 Welding processes and associated discontinuities

    16.1 SAW
    16.2 SMAW
    16.4 Special welding processes – Electron beam, electroslag etc.

    17.0 Introduction to Codes, Standards, Specifications and Procedures

    17.1 Discussion on ASTM E 215, ASME Section V
    17.2 Question answer session on above codes
    17.3 Interpretation / Evaluation
    17.4 Materials processing as it affects use of item and test results
    17.5 Discontinuities, their causes and effects
    17.6 Recognizing discontinuity indications
    17.7 Nonrelevant indications
    17.8 Relevant indications

    18.0 Acceptance criteria

    19.0 Report preparation

    NDTTECH recommended training time for Level I / II – 64 – 80 Hours ( 8/10 Days
    minimum). Recommended training references: (1) ASNT Handbook on ET (2) Nondestructive Testing hand book, Robert Mc Master (3) SNT TC 1A