Eddy Current Testing (ECT) Training: 8 Day Level II Course in Mumbai and Nagpur

Eddy Current Testing (ECT) and Phased Array Eddy Current Testing (PAECT) Level II Training: 8 day batch in Mumbai and Nagpur

Eddy Current Testing (ECT) uses electromagnetic induction to find surface and near surface cracks in conductive metals, and to measure coating thickness, material thickness, electrical conductivity and heat treatment condition. An alternating current in a test coil sets up a changing magnetic field. Bring that coil near a conductive part and the field induces circulating currents in the metal. These are eddy currents, and they generate their own magnetic field that opposes the coil field. A crack, a change in conductivity, a change in wall thickness or a change in the distance between coil and part shifts the impedance of the coil, and the instrument displays that shift. It is the method chosen for fatigue cracks in aircraft structure and fastener holes, for inspecting condenser tubing from one side, and for sorting aluminium alloys before assembly.

ECT finds tight surface cracks without contact, without couplant and without radiation, and it answers while the probe is still moving. Spark Institute of Nondestructive Testing runs an 8 day Eddy Current Testing course at Level II covering induction, impedance and phase analysis, skin depth, probe selection, reference standards and reporting, with hands on practice on meters, eddy current scopes, surface, bobbin and encircling probes, and crack, thickness and coating standards. The course also covers Phased Array Eddy Current Testing (PAECT), the eddy current array technique used for fast coverage of large areas and for encoded C-scan data imaging.

Looking for Eddy Current Testing training in India? Write to info@sparkndt.com or call +91 82080 65586 for fees, eligibility and the next batch, or use our contact page.

ECT Training Course Details

Course	Eddy Current Testing (ECT), Level II, including Phased Array Eddy Current Testing (PAECT)
Course duration	8 days
Training mode	Online live and offline classroom, plus hands on instrument, probe and interpretation practice
Equipment covered	Analog and digital eddy current meters, portable eddy current scopes with impedance plane display, dual and multi frequency instruments, and surface, I.D. bobbin, O.D. encircling, absolute, differential and reflection probes
Advanced technique	Phased Array Eddy Current Testing (PAECT), also called eddy current array or ECA: multi element probes, coil multiplexing, encoded scanning and C-scan imaging
Trainer	ASNT Level II qualified ECT trainers, with ASNT Level III qualified NDT staff at the institute
Standards covered	ASNT SNT-TC-1A, ISO 17643 for eddy current examination of welds by complex plane analysis, ASME BPVC Section V Article 8, and ASTM E426 for seamless and welded tube
Locations	Mumbai and Nagpur, Maharashtra
Prerequisite	None. Training and examination are matched to your employer written practice under ASNT SNT-TC-1A
Enquiries	info@sparkndt.com, +91 82080 65586

What You Will Learn in ECT Training

How an alternating current in a coil induces eddy currents that oppose the coil field, on Faraday’s law of induction and Lenz’s law.
How to calculate coil impedance, using inductive reactance XL = 2 pi f L and impedance as the square root of R squared plus XL squared.
How to read an impedance plane diagram, and how a crack, a lift-off change and a conductivity change each move the trace in their own direction.
Phase angle and phase lag, standard depth of penetration, and how frequency, conductivity and permeability together decide how deep you can see and how tight a crack you can find.
Probe selection across surface, I.D. bobbin and O.D. encircling probes, absolute, differential and reflection arrangements, fill factor, centring and edge effect.
Phased Array Eddy Current Testing (PAECT): how eddy current array probes are laid out, how multiplexing switches the coils, and how an encoded array scan is set up, balanced and read as a C-scan image.
Reference standards, balancing and sensitivity settings, and how to report indications against the standard and the applicable code.

Eddy Current Testing Course Syllabus

Introduction and history: electromagnetism as the basis of the method, from Faraday’s 1831 work on induction and Hughes’s 1879 observation of coil response near metals of differing conductivity, to growth from the 1950s in the aircraft and nuclear industries.
Principle of eddy current testing: alternating current in the test coil, induced current in a nearby conductor, eddy currents as closed loops in planes perpendicular to the flux, and the Lenz’s law reduction of coil inductance.
Impedance, resistance and reactance on the impedance plane: the four quantities Z, R, XL and phase angle, XL = 2 pi f L, the empty coil air point, the loaded coil, the shift from a crack, and the difference between aluminium and steel.
Phase angle and phase lag: 57 degrees of lag at one standard depth of penetration and 114 degrees at two, and depth estimation from phase.
Depth of penetration and frequency selection: the 37 percent rule, the skin depth formula, the effect of frequency, conductivity and permeability, and the trade off between penetration and sensitivity.
Variables that affect eddy currents: conductivity, permeability, lift-off, heat treatment and hardness, surface finish, part geometry, and the size and orientation of the defect.
Instrumentation: analog and digital meters, portable eddy current scopes, and single, dual and multi frequency instruments.
Probes and coil arrangements: surface, I.D. bobbin and O.D. encircling probes, sliding, ring and hole probes for fastener holes, absolute, differential and reflection arrangements, and fill factor.
Reference standards, technique and reporting: crack, thickness, conductivity and coating standards of the same or similar material, balancing and sensitivity, precautions against lift-off and edge effect, and interpretation and reporting to ISO 17643 and ASTM E426.
Phased Array Eddy Current Testing (PAECT): eddy current array probe construction and layouts, multiplexing of coils and mutual coupling, channel and drive frequency selection, encoded scan plans and coverage, C-scan and impedance plane display, sizing and reporting array data, and the limits of the technique.

How ECT Works: Impedance, Phase and Skin Depth

The coil resists current flow by its impedance Z, made up of circuit resistance R and coil inductive reactance XL, where XL = 2 pi f L and impedance is the square root of R squared plus XL squared. A worked example from the course: a coil of 6 ohms resistance and 4 microhenries inductance driven at 1 MHz gives a reactance of 25.13 ohms and an impedance of 25.85 ohms. The coil is strongly inductive, and the instrument must compensate for that before it can read a flaw.

Impedance is plotted on the impedance plane, resistance on one axis and reactance on the other, so each condition at the material maps to a point. On aluminium the resistance rises, because eddy currents draw energy from the coil, while reactance falls, because the eddy current field opposes the coil field. On steel the reactance rises instead, because the permeability of the steel concentrates the coil field and that gain outweighs the opposing field. Introduce a crack, fewer eddy currents can form, so resistance drops back and reactance rises again. Lift-off, conductivity and a crack each move the trace in a different direction, which is why phase is what separates them, and why ISO 17643 specifies examination of welds by complex plane analysis rather than by amplitude alone.

ECT is a surface and near surface method, because current density falls off exponentially below the surface. The standard depth of penetration, or skin depth, is where current density has fallen to 37 percent of the surface value, and it equals 1 divided by the square root of pi f mu sigma, with f in hertz, mu in henries per metre and sigma in siemens per metre. The higher the frequency, conductivity or permeability, the shallower the penetration, so on non magnetic materials, where relative permeability is close to one, the frequency sets the depth. Two rules follow, and the course drills both: for flaw detection, choose a frequency that puts the expected flaw depth within one standard depth of penetration; for conductivity measurement, choose one that gives about three standard depths.

Eddy Current Probes and Coil Arrangements

Surface probes: a coil near one end of a plastic housing, moved over the surface. Sliding, ring and hole probes are made for fastener holes.
I.D. bobbin probes: coils wound around a plastic former and inserted into tube, bar and hole to inspect from the inside, the standard probe for condenser, boiler and heat exchanger tubing.
O.D. encircling probes: coils on a hollow fixture so the part passes through the coil, used for tube, bar and rod at speed. With encircling and internal coils the fill factor, the ratio of the cross sectional area of the article to the coil opening area, governs how strongly the part couples to the coil.
Absolute probes: one coil generates the eddy currents and senses the reaction of the part, used for flaw detection, conductivity, lift-off and thickness.
Differential probes: two active coils wound in opposition, so the signals cancel over uniform material and a signal appears when one coil is over a defect and the other over sound material.
Reflection probes: driver and pickup coils, one exciting the eddy currents and the other sensing changes, so a driver can be built for a strong uniform field and a pickup made small and sensitive to small defects.

Phased Array Eddy Current Testing (PAECT) Training

Phased Array Eddy Current Testing (PAECT), also sold as eddy current array or ECA, replaces the single coil of a pencil probe with a row or grid of small coils on a flexible printed circuit. A multiplexer switches those coils on and off in a set sequence, so that some coils are live while their neighbours are idle. That keeps the coils from coupling into each other, and the instrument records a channel for every coil or coil pair in use.

The name is borrowed from ultrasonic testing, and the comparison has a limit worth teaching. Phased array ultrasonics delays each element so that the sound beam steers and focuses inside the metal. Eddy currents do not travel as a steerable beam, so PAECT gains its advantage a different way: through coverage, consistency and data. One pass of an array probe covers a band that would need several overlapping scans with a pencil probe, the scan pattern is simpler, results vary less from one inspector to the next, and encoded array data gives a C-scan map of the tested area that can be measured, reviewed and archived.

Spark NDT teaches PAECT on top of the Level II ECT fundamentals, because the same variables still govern the result: frequency, lift-off, conductivity, permeability, edge effect and phase response. The array adds probe and channel decisions above them. PAECT is a technique inside the eddy current (ET) method, so personnel qualification stays with ET under ASNT SNT-TC-1A instead of a separate method, and array training and experience are recorded under ET in the written practice.

Array probe types and layouts: surface arrays, flex probes that conform to curved and double curved structure, tube and rod arrays, and arrays shaped for welds, lap joints and edges.
Multiplexing schemes: which coils fire together, which fire in sequence, mutual coupling between neighbouring coils, and why the scheme belongs in the written procedure.
Setup and calibration: drive frequency and channel selection across the array, balancing each channel, and sensitivity checks on reference standards with notches of known depth.
Encoded scanning: scan plans, coverage, overlap, scan speed, and setting the instrument so that one defect gives a repeatable response on every channel.
Data views and reporting: C-scan and impedance plane display, phase and frequency filtering, sizing against the standard, and reporting array data for review.
Limits: where a single coil probe is still the better choice, including small fastener holes, tight access, thick coatings and coarse or strongly magnetic geometry.

Applications of Eddy Current Testing

Surface and near surface crack detection in welds, heat affected zones, parent metal, bolt holes, machined parts and castings, in ferrous and non ferrous metals.
Aerospace structure and engines: fatigue cracks in skin and fastener holes, and gas turbine disc bolt holes where crack lengths down to 0.023 inches are detected reliably.
Condenser, heater and exchanger tubing in power, chemical and petrochemical plants, examined from one side at 200 to 300 mm per second, with the f90 frequency separating inside surface thinning from outside surface thinning.
Automated tube, bar and wire inspection at line speeds up to 3 metres per second, with magnetic saturation and demagnetisation for ferrous product.
Corrosion and thickness measurement in thin sections such as tube, sheet and aircraft skin, and non conductive coating thickness on conductive metal to better than one mil.
Material identification and sorting: ferrous segregators and sorting bridges for hardened steel, and conductivity meters for aluminium and copper alloys, sorted on composition and hardness variation, heat treatment condition and cladding thickness.

Advantages and Limitations of Eddy Current Testing

Sensitive to small cracks and other discontinuities, and effective on surface and near surface defects.
Immediate results on very portable equipment, with minimum part preparation, and no couplant, chemical developer or radiation control.
Complex shapes of conductive material can be inspected, and the method covers far more than flaw detection: thickness, coating thickness, conductivity, sorting and heat treatment condition.
Only conductive materials can be inspected and the surface must be accessible to the probe; depth of penetration is limited, flaws lying parallel to the coil winding and scan direction are missed, and reference standards are needed for set up.
The skill required is greater than for several other NDT methods, because the operator reads phase as well as amplitude and must know which variable is producing the signal.
Lift-off, edge effect, conductivity variation, temperature and nearby magnetic fields all produce signals that have to be recognised and rejected, which is why the course drills precautions such as working on a non conductive bench and keeping other conductive parts clear of the coil.

Training, Examination and Qualification

Spark Institute of Nondestructive Testing trains and examines Eddy Current Testing to Level II, and provides the training and examination documentation your employer needs to grant ASNT SNT-TC-1A certification. The institute records the syllabus covered, the hours worked, the practical exercises completed and the examination result.

Frequently Asked Questions

How long is the Eddy Current Testing course at Spark NDT?

The Eddy Current Testing course runs 8 days at Level II. See the course durations for other methods, and contact us for the current batch calendar.

Which materials can be tested by eddy current testing?

Any conductive material: aluminium, magnesium, copper, brass, titanium, austenitic stainless steel, and carbon and low alloy steel. Plastics, ceramics, glass and dry concrete cannot be examined this way. On ferromagnetic steel, high permeability confines the response to the surface unless the area is saturated by a magnet.

How deep can eddy current testing detect a crack?

Within about one standard depth of penetration, the depth at which current density has fallen to 37 percent of the surface value. That depth depends on test frequency, conductivity and permeability, so a lower frequency looks deeper and a higher frequency gives greater surface sensitivity at the cost of depth. Choosing the frequency is the first decision in any ECT procedure, and the first thing a candidate is examined on.

Does eddy current testing work through paint?

Yes, through non conductive coatings. The coating displaces the probe from the base metal and weakens the eddy currents in proportion to its thickness, which is the same effect used to measure coating thickness to better than one mil. The frequency and sensitivity are set with the coating in place.

What is the impedance plane and why does phase matter?

The impedance plane plots coil resistance on one axis and inductive reactance on the other, so every condition at the probe gives a point on that plane. A lift-off change, a conductivity change and a crack each move the point in a different direction, and phase angle is how they are told apart. With amplitude alone you have a signal and no way to say what caused it.

Is online Eddy Current Testing training available?

Theory, impedance plane work and data interpretation are delivered online live where required, and offline classroom training with hands on instrument, probe and reference standard practice runs at Mumbai and Nagpur. Confirm which sessions require in person attendance for your batch.

What is Phased Array Eddy Current Testing (PAECT)?

PAECT, also called eddy current array or ECA, uses a probe with many small coils instead of one. A multiplexer energises those coils in a set sequence, so a single pass covers a wide band instead of the narrow line a pencil probe traces, and the overlapping repeat scans are not needed. That gives faster coverage of large areas, more consistent results between inspectors, and encoded C-scan images that can be measured and kept as a record. PAECT is a technique within the eddy current method, so candidates qualify in ET rather than in a separate method. Spark NDT covers PAECT inside the Eddy Current Testing Level II course at Mumbai and Nagpur.

Enquire About Eddy Current Testing Training

For the syllabus, fees, hostel guidance and the next Eddy Current Testing batch in Mumbai or Nagpur, write to info@sparkndt.com or call +91 82080 65586. Company and on-site batches are arranged for teams; the full method list is on our course durations and syllabus page.

Spark Institute of Nondestructive Testing
Email: info@sparkndt.com
Website: sparkndt.com
Training locations: Mumbai and Nagpur, Maharashtra.

Contact Spark NDT today to enquire about the next Eddy Current Testing training batch.