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100+ Free ASNT NDT III ET Practice Questions

Pass your ASNT NDT Level III Electromagnetic / Eddy Current Testing (ET) Method Examination exam on the first try — instant access, no signup required.

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What is the primary benefit of an eddy current array (ECA) probe over a single surface coil for in-service surface scanning?

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2026 Statistics

Key Facts: ASNT NDT III ET Exam

135

Multiple-Choice Questions

ASNT NDT Level III method exam

4 hrs

Exam Time Limit

ASNT Pearson VUE format

70%

Passing Score

ASNT certification rules

Basic

Exam Required First

ASNT method-exam prerequisite

5 yrs

Typical Recert Cycle

ASNT Level III certification

Pearson VUE

CBT Test Provider

ASNT testing partner

As of 2026, the ASNT NDT Level III ET method exam is a 135-question, 4-hour Pearson VUE CBT requiring 70% to pass and the Basic examination as a prerequisite. Expect heavy coverage of electromagnetic induction and skin depth (delta = 503/sqrt(sigma*mu*f)), impedance-plane interpretation, lift-off and fill factor, surface/bobbin/encircling/array probes, frequency selection and multifrequency mix-out, EDM-notch and drilled-hole calibration, IACS conductivity measurement, coating thickness, alloy sorting, heat-treat verification, tubing inspection, and acceptance criteria from ASME Section V Article 8 plus ASTM E309, E243, and E2210.

Sample ASNT NDT III ET Practice Questions

Try these sample questions to test your ASNT NDT III ET exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Which physical law explains why a changing magnetic field induces eddy currents in a nearby conductor?
A.Ohm's law
B.Faraday's law of electromagnetic induction
C.Coulomb's law of electrostatics
D.Kirchhoff's current law
Explanation: Faraday's law states that a time-varying magnetic flux through a conductive region induces an electromotive force, which drives circulating eddy currents. Ohm's, Coulomb's, and Kirchhoff's laws describe other electrical relationships but not the induction mechanism itself.
2What does Lenz's law tell you about the direction of eddy currents induced in a conductor by an approaching probe coil?
A.Their direction depends only on temperature, not on probe motion
B.They flow in the same direction as the probe current to reinforce the field
C.They flow in a direction that opposes the change in the original magnetic flux
D.They flow only along the surface in the direction of probe motion
Explanation: Lenz's law says the induced current direction always opposes the change in flux that produced it. That opposition is what creates a secondary field the eddy current instrument can detect through its effect on coil impedance.
3Using the standard depth-of-penetration relationship delta = 503 / sqrt(sigma * mu_r * f), with sigma in S/m, what happens to skin depth when frequency is quadrupled and all other variables are held constant?
A.Skin depth is reduced by a factor of four
B.Skin depth is unchanged
C.Skin depth doubles
D.Skin depth is halved
Explanation: Because skin depth varies as 1/sqrt(f), multiplying the frequency by four multiplies the denominator by sqrt(4) = 2, so the resulting skin depth is one half of the original value.
4A bobbin coil with inside diameter 14.0 mm inspects a tube whose outside diameter is 15.9 mm. What is the fill factor?
A.Approximately 1.13
B.Approximately 0.78
C.Approximately 0.88
D.Approximately 0.93
Explanation: Bobbin fill factor is (coil ID / tube OD)^2 = (14.0 / 15.9)^2 = (0.8805)^2 which is about 0.78. Higher fill factor gives more sensitivity but less clearance to pull the probe through the tube.
5On a standard impedance-plane display for a surface coil on a nonferromagnetic conductor, which axis is typically shown vertical and which horizontal?
A.Vertical = current, horizontal = voltage
B.Vertical = resistive component, horizontal = inductive reactance
C.Vertical = inductive reactance, horizontal = resistive component
D.Vertical = phase angle, horizontal = lift-off only
Explanation: By convention the inductive reactance (omega*L) is plotted on the vertical axis and the resistive component (R) on the horizontal axis. Changes in conductivity, lift-off, and discontinuities all appear as movement of the operating point on this plane.
6On the conductivity locus of an impedance plane, where does a high-conductivity material like pure copper plot relative to a low-conductivity material like Inconel?
A.Off the locus, on the negative resistance side
B.At the origin regardless of conductivity
C.Higher on the locus, near the top of the curve
D.Lower on the locus, away from the top
Explanation: On the standard normalized conductivity curve, the air point is at the top of the curve. As conductivity increases, the operating point moves down and around the curve, so copper plots lower on the locus than Inconel.
7Lift-off describes which physical condition during a surface-coil inspection?
A.The probe-to-conductor stand-off distance through any nonconductive layer
B.Variation in coil inductance with temperature
C.Change in tube wall thickness during scanning
D.Probe motion parallel to the surface
Explanation: Lift-off is the gap between the coil and the conductive surface, whether from coating, paint, dirt, or operator inconsistency. It produces a characteristic signal direction on the impedance plane that operators rotate out so that defect signals remain visible.
8Calculate the standard depth of penetration in 304 stainless steel (sigma about 1.39 x 10^6 S/m, mu_r about 1) at 100 kHz, using delta = 503 / sqrt(sigma * mu_r * f) with sigma in S/m.
A.Approximately 13 mm
B.Approximately 0.4 mm
C.Approximately 1.3 mm
D.Approximately 4.3 mm
Explanation: Compute sigma*mu_r*f = 1.39e6 * 1 * 1.0e5 = 1.39e11. The square root is about 3.73e5. Skin depth = 503 / 3.73e5 = 1.35e-3 m, which is about 1.3 mm. Stainless's low conductivity makes ET useful at moderate frequencies.
9Why does ferromagnetic material (mu_r much greater than 1) produce a very small skin depth at the same frequency compared with a nonmagnetic conductor of similar conductivity?
A.Because Lenz's law does not apply to ferromagnetic material
B.Because eddy currents only flow in nonmagnetic materials
C.Because the impedance plane collapses to a single point
D.Because permeability appears under the square root in the denominator of the skin depth formula
Explanation: In the formula delta = 503/sqrt(sigma*mu_r*f), increasing mu_r by hundreds or thousands shrinks the skin depth dramatically. That is why ferromagnetic tubing often requires magnetic saturation or remote-field techniques to inspect.
10What is the approximate phase angle between the surface eddy current density and the current one skin depth below the surface?
A.57 degrees (1 radian)
B.90 degrees
C.0 degrees
D.45 degrees
Explanation: By definition, one skin depth corresponds to a 1 / e amplitude reduction and a phase lag of 1 radian, about 57 degrees. This phase lag versus depth is what enables phase-angle depth sizing of cracks.

About the ASNT NDT III ET Exam

The ASNT NDT Level III Electromagnetic / Eddy Current Testing method examination certifies candidates with Level III responsibility for ET procedures, technique selection, calibration, conductivity and thickness measurement, and acceptance interpretation. Candidates must first pass the ASNT Basic exam, then sit the ET method exam at a Pearson VUE test center.

Assessment

135 multiple-choice questions covering ET theory, probes and coils, instruments and display, calibration, applications, tube inspection, and applicable codes/standards.

Time Limit

4 hours

Passing Score

70%

Exam Fee

Tiered ASNT member/non-member fees (ASNT (American Society for Nondestructive Testing))

ASNT NDT III ET Exam Content Outline

18% topic emphasis

ET Theory & Physics

Electromagnetic induction; Faraday's and Lenz's laws; primary/secondary fields; skin depth delta = 503/sqrt(sigma*mu*f); impedance plane behavior; lift-off and fill factor; conductivity (sigma) and relative permeability (mu_r) effects.

16% topic emphasis

Probes & Coils

Surface, bobbin, encircling, and array probes; absolute vs differential configurations; reflection (driver/pickup) and send-receive arrangements; shielding; and bobbin fill factor for tubing.

16% topic emphasis

Instruments & Display

Impedance-plane vector display, vertical/horizontal phase axes, gain, phase rotation, frequency selection, multifrequency mixing for support-plate suppression, and strip-chart presentations.

14% topic emphasis

Calibration & References

EDM notch and through-wall/flat-bottom drilled-hole standards, ASME tubing standards, frequency optimization to balance penetration and resolution, and mix-out of unwanted signals.

14% topic emphasis

Applications

Thickness gauging, IACS conductivity measurement, nonconductive coating thickness over conductive substrates, alloy sorting, and heat-treat verification.

14% topic emphasis

Tube Inspection

Heat-exchanger and condenser tubing with bobbin probes, in-service inspection per ASME Section V Article 8, signal interpretation for ID/OD pitting, wall loss, and support-plate effects.

8% topic emphasis

Codes & Standards

ASME Section V Article 8 eddy current examination of tubular products, ASTM E309 (electromagnetic examination of steel products with magnetic saturation), ASTM E243 (electromagnetic examination of seamless and welded copper and copper-alloy tubular products), and ASTM E2210 (array eddy current practice).

How to Pass the ASNT NDT III ET Exam

What You Need to Know

  • Passing score: 70%
  • Assessment: 135 multiple-choice questions covering ET theory, probes and coils, instruments and display, calibration, applications, tube inspection, and applicable codes/standards.
  • Time limit: 4 hours
  • Exam fee: Tiered ASNT member/non-member fees

Keys to Passing

  • Complete 500+ practice questions
  • Score 80%+ consistently before scheduling
  • Focus on highest-weighted sections
  • Use our AI tutor for tough concepts

ASNT NDT III ET Study Tips from Top Performers

1Memorize the standard depth formula delta = 503/sqrt(sigma*mu_r*f) and practice both directions: given a target depth, solve for frequency; given a frequency, predict penetration.
2Build an impedance-plane mental model with conductivity locus, lift-off direction, and crack signal direction so you can phase-rotate signals quickly.
3Drill bobbin fill factor calculations and know that higher fill factor improves sensitivity but reduces probe-pull clearance.
4Compare absolute vs differential probe responses: differential cancels gradual wall thinning and emphasizes localized discontinuities.
5Practice multifrequency mix-out logic: subtract a support-plate signal acquired at one frequency from data at the inspection frequency to isolate tubing defects.
6Review ASME Section V Article 8 mandatory reference standards (EDM notches and through-wall holes) and the signal-to-noise requirements they impose.
7Memorize key conductivities: copper 100% IACS reference, aluminum alloys roughly 30 to 60% IACS, titanium and stainless under 5% IACS.
8Work timed 135-question practice sets to pace at roughly 1.7 minutes per question while leaving review margin.

Frequently Asked Questions

How many questions are on the ASNT NDT Level III ET method exam?

The Level III ET method examination is 135 multiple-choice questions delivered as a Pearson VUE computer-based test. Candidates have 4 hours to complete the exam, and a 70% score is required to pass.

Do I need to pass the ASNT Basic exam first?

Yes. ASNT requires candidates to pass the NDT Level III Basic examination before sitting any method examination, including ET. The Basic exam covers SNT-TC-1A practice, materials, processes, and general NDT methods.

What does the ET method exam cover?

Expect electromagnetic induction theory, skin depth calculations, impedance-plane interpretation, lift-off and fill-factor effects, surface and bobbin and encircling and array probes, absolute vs differential configurations, frequency selection and multifrequency mix-out, EDM-notch and drilled-hole calibration, conductivity in %IACS, coating thickness, tubing inspection, and acceptance criteria from ASME Section V Article 8 plus ASTM E309, E243, and E2210.

Where do I take the exam?

ASNT delivers Level III method exams through Pearson VUE test centers worldwide. Candidates schedule the exam after ASNT approves their application and prerequisites are met.

How long is the Level III ET certification valid?

ASNT Level III certificates are typically valid for five years before recertification. Candidates can renew by reexamination or, where allowed, by approved continuing professional development under current ASNT recertification rules.

How much does the exam cost?

ASNT uses tiered member and non-member fees for the Level III method examinations. Refer to the current ASNT certification fee schedule for exact totals, as fees may include the Basic exam, method exam, and recertification when applicable.

What math should I be ready to do quickly?

Master the standard depth of penetration formula delta = 503/sqrt(sigma_S/m * mu_r * f_Hz) or equivalent SI form, fill factor eta = (D_coil_inside/D_tube_outside)^2 for bobbin probes, and basic %IACS conversions where 100% IACS equals 5.8 x 10^7 S/m. Many calculation items test phase angle behavior with increasing frequency or conductivity.