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ASNT NDT Level II study materials
ASNT NDT Level II study resources

ASNT NDT Level II practice questions

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Question 1Electromagnetic Testing (ET)

In eddy current testing, how is eddy current density distributed through the thickness of a conductor?

  1. It is uniform throughout the thickness
  2. It is present only along sharp edges
  3. It is concentrated only at the center
  4. It is highest at the surface and decreases with depth Correct answer.

Explanation

The alternating field and the eddy currents it induces are strongest at the surface and attenuate exponentially with depth. This attenuation is described by the standard depth of penetration.

Question 2Electromagnetic Testing (ET)

Eddy currents are induced in a test object by:

  1. A steady DC magnetic field
  2. An alternating magnetic field Correct answer.
  3. Gamma radiation
  4. A constant current passed through the specimen

Explanation

Eddy currents are induced by a time-varying magnetic field, which is produced by an alternating current in the test coil. A steady DC field does not induce continuous eddy currents.

Question 3Electromagnetic Testing (ET)

Increasing lift-off between a surface probe coil and a conductive specimen generally causes the coil inductance to:

  1. Increase toward its air-core value Correct answer.
  2. Remain exactly constant
  3. Decrease toward zero
  4. Become purely resistive

Explanation

Lift-off reduces magnetic coupling between the coil and the specimen, so the opposing eddy currents are weaker and the coil inductance rises toward its air-core value. This is why lift-off is a major source of unwanted signal variation.

Question 4Electromagnetic Testing (ET)

Fill factor in an encircling coil inspection is defined as the ratio of:

  1. Test frequency to cutoff frequency
  2. Lift-off to coil diameter
  3. Specimen cross-sectional area to coil inside area Correct answer.
  4. Coil length to specimen length

Explanation

Fill factor expresses how completely the specimen fills the coil opening. A high fill factor means better magnetic coupling and a stronger eddy current signal.

Question 5Electromagnetic Testing (ET)

As eddy currents penetrate deeper into a conductor, their phase:

  1. Leads the surface current
  2. Remains constant with depth
  3. Reverses by 180 degrees at one skin depth
  4. Lags progressively behind the surface current Correct answer.

Explanation

Eddy currents at greater depth are delayed relative to those at the surface, so their phase lags progressively with depth. This phase-depth relationship is the basis for depth estimation in impedance-plane analysis.

Question 6Electromagnetic Testing (ET)

Why is magnetic saturation sometimes applied when eddy current testing ferromagnetic materials?

  1. To eliminate the need for reference standards
  2. To increase lift-off during scanning
  3. To reduce permeability variations that cause noise Correct answer.
  4. To increase the electrical conductivity of the part

Explanation

Ferromagnetic materials have high and variable permeability, which can dominate the eddy current signal and mask defects. Saturating the material makes permeability more uniform and reduces this noise source.

Question 7Electromagnetic Testing (ET)

A differential eddy current coil arrangement is best suited for:

  1. Detecting small localized defects while suppressing gradual dimensional changes Correct answer.
  2. Detecting gradual changes in wall thickness
  3. Measuring absolute conductivity at a single spot
  4. Inspecting only nonconductive materials

Explanation

A differential coil compares two adjacent regions, so a localized defect produces a strong signal while gradual changes common to both regions tend to cancel. This makes it effective for small defects such as cracks.

Question 8Electromagnetic Testing (ET)

Eddy current conductivity measurements are commonly used to:

  1. Detect surface cracks only
  2. Determine wall thickness only
  3. Sort alloys by electrical conductivity Correct answer.
  4. Measure magnetic permeability of ferromagnetic materials

Explanation

Different alloys and heat treatments have characteristic electrical conductivities, so eddy current measurements can be used for material sorting and verification. Conductivity is one of the primary material properties affecting the eddy current response.

Question 9Electromagnetic Testing (ET)

To increase the depth of penetration in a given nonmagnetic conductor, the test frequency should be:

  1. Held constant regardless of material
  2. Decreased Correct answer.
  3. Increased
  4. Set to the coil self-resonant frequency

Explanation

Depth of penetration is inversely proportional to the square root of frequency, so lowering the frequency increases penetration. The tradeoff is reduced sensitivity to small near-surface defects.

Question 10Electromagnetic Testing (ET)

An edge effect signal occurs when a coil approaches:

  1. A weld with different conductivity
  2. A magnetic chuck used for holding
  3. The end or boundary of the test object Correct answer.
  4. A region of uniform thickness

Explanation

Near the end or edge of a part, the eddy current paths are distorted because the conductive material is no longer continuous. This produces a signal that can be mistaken for a defect unless the edge is recognized or avoided.

Question 11Electromagnetic Testing (ET)

In impedance-plane analysis, the phase angle of a defect signal is used primarily to estimate:

  1. Defect width
  2. Defect depth Correct answer.
  3. Coating hardness
  4. Defect length

Explanation

Because eddy current phase lags progressively with depth, the phase angle of a defect signal can be related to how deep the defect lies. Amplitude alone is less reliable for depth estimation because it also depends on defect size and coupling.

Question 12Electromagnetic Testing (ET)

An absolute eddy current coil is generally preferred for:

  1. Suppressing lift-off variations
  2. Detecting tiny cracks in a highly uniform region
  3. Comparing two adjacent regions directly
  4. Sorting materials and measuring properties that change gradually Correct answer.

Explanation

An absolute coil responds to the total coil-to-specimen condition, making it useful for material sorting, conductivity measurement, and other gradual property changes. It is less effective than a differential coil for isolating very small localized defects.

Question 13Electromagnetic Testing (ET)

For a surface-breaking crack in a nonmagnetic metal inspected with a surface probe, the eddy current signal on the impedance plane generally shows:

  1. No phase change with depth
  2. A change in both resistance and inductive reactance components whose phase depends on depth Correct answer.
  3. Only an inductive reactance change
  4. Only a resistance change

Explanation

A crack interrupts eddy current flow and changes both the resistive loss and the inductive coupling seen by the coil. The resulting impedance-plane signal has a phase angle that depends on defect depth and geometry.

Question 14Electromagnetic Testing (ET)

A bobbin coil is typically used to inspect:

  1. External threads
  2. Only nonconductive composites
  3. The inside of heat exchanger tubes Correct answer.
  4. Flat plate lap joints

Explanation

A bobbin coil is a small encircling coil that is pulled or pushed through the bore of a tube. It is widely used for heat exchanger and condenser tube inspection.

Question 15Electromagnetic Testing (ET)

In remote-field eddy current testing of ferromagnetic tubes, the exciter and detector coils are separated by approximately:

  1. Two tube diameters Correct answer.
  2. One coil diameter
  3. Ten skin depths
  4. One wall thickness

Explanation

Remote-field testing uses a separation of about two tube diameters so the detector operates in the remote-field region, where the indirect field has penetrated through the tube wall. This allows inspection of the full wall thickness.

Question 16Electromagnetic Testing (ET)

Reference standards for eddy current tube inspection usually contain:

  1. A tube with known permeability only
  2. Radiographic film
  3. Only a smooth defect-free tube
  4. Artificial defects such as drilled holes or EDM notches Correct answer.

Explanation

Reference standards contain artificial defects of known size and location so the inspection system can be set to a repeatable sensitivity. Drilled holes and EDM notches are common because they simulate service defects.

Question 17Electromagnetic Testing (ET)

A surface probe coil is designed to:

  1. Inspect only the far wall of thick tubes
  2. Operate only with direct current
  3. Operate with small lift-off and inspect near-surface regions Correct answer.
  4. Require a fill factor above 90 percent

Explanation

Surface probes are placed close to the specimen to concentrate eddy currents in the near-surface region. They are used for crack detection, conductivity measurement, and coating thickness assessment.

Question 18Electromagnetic Testing (ET)

Which practice most directly improves signal-to-noise ratio when an eddy current defect signal is weak?

  1. Averaging repeated scans and filtering at the optimum frequency Correct answer.
  2. Increasing scan speed without averaging
  3. Using a larger fill factor in a surface probe
  4. Increasing lift-off

Explanation

Averaging reduces random noise, and filtering removes frequency components outside the defect signal band. Choosing an optimum test frequency also maximizes the defect response relative to noise.

Question 19Electromagnetic Testing (ET)

A through-coil (encircling) inspection is generally used for:

  1. Only nonmagnetic materials
  2. Inspecting the inside surface of small holes
  3. Measuring coating thickness on a flat plate
  4. Inspecting the full circumference of bar, wire, or tube Correct answer.

Explanation

An encircling coil surrounds the product and induces eddy currents around its full circumference. This makes it suitable for continuous inspection of bar, wire, and tube.

Question 20Electromagnetic Testing (ET)

After using DC magnetic saturation to inspect a ferromagnetic part, the part should usually be:

  1. Demagnetized Correct answer.
  2. Inspected at a higher frequency
  3. Heated above the Curie temperature
  4. Re-magnetized to saturation

Explanation

The strong DC field used for saturation can leave residual magnetism in the part. Demagnetization restores the part to a low-remanence condition, which is often required before further processing or use.

Question 21Electromagnetic Testing (ET)

Using the approximation δ = 50.3 sqrt(ρ/(μr f)), where δ is in mm, ρ is in microhm-centimeters, and f is in Hz, what is the standard depth of penetration in aluminum (ρ = 2.8 microhm-cm, μr = 1) at 1000 Hz?

  1. About 8.4 mm
  2. About 2.7 mm Correct answer.
  3. About 27 mm
  4. About 0.27 mm

Explanation

Substituting gives δ = 50.3 sqrt(2.8/1000) = 50.3 times 0.0529, which is about 2.7 mm. This illustrates how frequency and conductivity set the effective inspection depth.

Question 22Electromagnetic Testing (ET)

At a depth equal to one standard depth of penetration, the eddy current phase lags the surface current by approximately:

  1. 180 degrees
  2. 90 degrees
  3. 57 degrees, or one radian Correct answer.
  4. 45 degrees

Explanation

The eddy current phase lag is approximately one radian per standard depth of penetration, and one radian is about 57.3 degrees. This relationship is the basis for estimating depth from impedance-plane phase.

Question 23Electromagnetic Testing (ET)

Two defects at different depths produce signals that are difficult to separate in phase. Which change would most improve depth discrimination near the surface?

  1. Decreasing conductivity
  2. Increasing coil diameter
  3. Increasing test frequency Correct answer.
  4. Increasing lift-off

Explanation

Increasing frequency reduces the skin depth, so the phase difference produced by a given depth interval becomes larger near the surface. This improves near-surface depth resolution, although penetration is reduced.

Question 24Electromagnetic Testing (ET)

A ferromagnetic tube is inspected with a conventional eddy current bobbin coil without magnetic saturation. The dominant cause of signal variation is most likely:

  1. Conductivity changes
  2. Cracks
  3. Wall thinning
  4. Permeability variations Correct answer.

Explanation

In unsaturated ferromagnetic materials, variations in magnetic permeability strongly affect coil impedance and can overwhelm defect signals. Saturation or magnetic bias is used to make permeability more uniform.

Question 25Electromagnetic Testing (ET)

In impedance-plane eddy current testing, the lift-off line for a surface coil is approximately:

  1. Identical to the defect signal for a deep crack
  2. A circle centered at the origin
  3. A line with a characteristic phase that can be rotated out to suppress lift-off effects Correct answer.
  4. A line at 45 degrees that applies only to ferromagnetic materials

Explanation

Lift-off produces a signal along a characteristic direction on the impedance plane, largely independent of frequency. Phase rotation can align this direction with a null so that lift-off changes are suppressed while defect signals remain visible.

Question 26Electromagnetic Testing (ET)

The impedance of an eddy current probe coil is made up of which two quantities?

  1. Resistance and inductive reactance Correct answer.
  2. Resistance and magnetostrictive loss
  3. Resistance and capacitive reactance
  4. Inductive reactance and capacitance

Explanation

A coil behaves as a resistor in series with an inductor, so its impedance is the vector combination of the winding resistance and the inductive reactance 2πfL. Eddy currents induced in the test object alter both the effective resistance and the effective inductance, which is what shifts the impedance point on the display.

Question 27Electromagnetic Testing (ET)

What is the main purpose of a ferrite core in an eddy current probe coil?

  1. It removes the need for a reference standard
  2. It allows the coil to operate without alternating current
  3. It concentrates the magnetic flux in the test region Correct answer.
  4. It converts the eddy current signal into a direct voltage

Explanation

Ferrite has high permeability and low loss, so it provides a low-reluctance path that concentrates and directs the coil's alternating field into the test region. This raises the flux density for a given excitation and usually improves sensitivity and field focus.

Question 28Electromagnetic Testing (ET)

Eddy currents are induced in a test object when the object is:

  1. Linked by a time-varying magnetic field Correct answer.
  2. Heated above its Curie temperature
  3. Made to carry direct current from an external supply
  4. Held in an unchanging magnetic field

Explanation

Faraday's law states that a changing magnetic flux linking a conductor induces a voltage, which drives circulating currents. In eddy current testing the changing flux is produced by the alternating current in the probe coil.

Question 29Electromagnetic Testing (ET)

Eddy current inspection of austenitic stainless steel weldments is more difficult than inspection of wrought plate mainly because:

  1. Permeability and conductivity vary locally Correct answer.
  2. The weld is much thicker than the base metal
  3. The alloy has unusually low electrical conductivity
  4. Eddy currents cannot be induced in austenitic alloys

Explanation

Weld metal and heat-affected zones in austenitic steels contain varying amounts of delta ferrite and have different grain structure, so permeability and conductivity change from point to point. These local changes produce coherent noise that can mask or mimic defect signals.

Question 30Electromagnetic Testing (ET)

In a modern eddy current instrument, the function of the phase-sensitive (synchronous) detector is to:

  1. Raise the test frequency to obtain deeper penetration
  2. Record the coil resistance permanently on a chart
  3. Generate the alternating current that drives the excitation coil
  4. Resolve the coil signal into in-phase and quadrature components Correct answer.

Explanation

A synchronous detector compares the coil signal with a reference phase and outputs two DC components, one in phase and one in quadrature. This allows the operator to display an impedance-plane signal and to suppress unwanted indications such as lift-off by phase discrimination.

Question 31Electromagnetic Testing (ET)

For an encircling coil, the fill factor is defined as the ratio of the:

  1. Test frequency to the coil resonant frequency
  2. Specimen length to the coil length
  3. Specimen conductivity to the coil inductance
  4. Coil cross-sectional area to the specimen cross-sectional area Correct answer.

Explanation

Fill factor expresses how completely the coil's cross section is occupied by the test object. A value close to one means the coil couples tightly to the specimen and produces a strong, sensitive response.

Question 32Electromagnetic Testing (ET)

When eddy current conductivity readings are compared between parts, the readings must normally be corrected for:

  1. Relative humidity
  2. Barometric pressure
  3. Ambient light level
  4. Specimen temperature Correct answer.

Explanation

Electrical conductivity in metals falls as temperature rises, typically by a few tenths of a percent per degree Celsius. Readings therefore must be normalised to a reference temperature, or the part and standard must be at the same temperature.

Question 33Electromagnetic Testing (ET)

Compared with a pickup coil, a Hall effect sensor used in electromagnetic testing has the advantage that it:

  1. Measures conductivity directly
  2. Responds to static fields over a wide frequency range Correct answer.
  3. Needs no excitation supply
  4. Induces currents in insulators

Explanation

A Hall element produces an output proportional to the absolute magnetic field, including steady fields, and its response stays flat over a broad frequency band. This makes it useful for measuring field strength directly in remote-field and flux-leakage applications where a coil's inductive response would fall off.

Question 34Electromagnetic Testing (ET)

The standard depth of penetration in a nonmagnetic alloy is 1.0 mm at 100 kHz. At 25 kHz, in the same material, it is approximately:

  1. 4.0 mm
  2. 2.0 mm Correct answer.
  3. 0.25 mm
  4. 1.0 mm

Explanation

Standard depth of penetration varies inversely with the square root of frequency. Reducing frequency from 100 kHz to 25 kHz divides it by four under the root, so the depth increases by a factor of two, from 1.0 mm to 2.0 mm.

Question 35Magnetic Particle Testing (MT)

For optimum detection, a discontinuity should lie in which orientation relative to the magnetizing field?

  1. At 45 degrees to the magnetic field
  2. Parallel to the magnetic field
  3. Perpendicular to the magnetic field Correct answer.
  4. Independent of the magnetic field

Explanation

A discontinuity is detected when it interrupts the field lines and causes flux to leak out of the surface. Leakage is greatest when the discontinuity lies at right angles to the field, so the field direction is chosen to cross the probable flaw orientation.

Question 36Magnetic Particle Testing (MT)

Which technique produces a circular magnetic field in the part?

  1. Placing a permanent magnet on the surface
  2. Passing current directly through the part Correct answer.
  3. Energizing an encircling coil around the part
  4. Positioning an electromagnetic yoke across the part

Explanation

Current flowing through the part generates a field that encircles the current path, so the field is circular in planes normal to the current. Coils and yokes instead produce longitudinal fields aligned with their axes or pole pieces.

Question 37Magnetic Particle Testing (MT)

The ultraviolet light used to evaluate fluorescent magnetic particle indications is normally centered at which wavelength?

  1. 254 nm
  2. 313 nm
  3. 450 nm
  4. 365 nm Correct answer.

Explanation

Fluorescent magnetic particle inspection uses UV-A radiation centered near 365 nm, which excites the fluorescent coating on the particles. The particles then emit visible yellow-green light that contrasts with the dark background.

Question 38Magnetic Particle Testing (MT)

What minimum ultraviolet intensity is required at the surface being examined during a fluorescent magnetic particle test?

  1. 100 microwatts per square centimeter
  2. 500 microwatts per square centimeter
  3. 300 microwatts per square centimeter
  4. 1000 microwatts per square centimeter Correct answer.

Explanation

Standard practice requires at least 1000 microwatts per square centimeter (10 W/m2) of UV-A incident on the inspection surface. The value is verified with a UV-A meter because lamp output falls with age and distance.

Question 39Magnetic Particle Testing (MT)

Which of the following materials can be inspected by the magnetic particle method?

  1. Austenitic stainless steel
  2. Copper
  3. Low-carbon steel Correct answer.
  4. Aluminum alloy

Explanation

Magnetic particle testing requires a ferromagnetic material that can be magnetized strongly enough to produce leakage fields at discontinuities. Low-carbon steel is ferromagnetic, whereas austenitic stainless steel, aluminum, and copper are not.

Question 40Magnetic Particle Testing (MT)

What is the principal advantage of the continuous magnetization technique compared with the residual technique?

  1. It produces a longitudinal field without a coil
  2. It can be applied to nonmagnetic materials
  3. It reveals indications on low-retentivity parts Correct answer.
  4. It eliminates the need to demagnetize the part afterward

Explanation

In the continuous technique the particles are applied while the magnetizing current flows, so the field is present to attract and hold particles even on materials that do not retain magnetism. This makes it more sensitive and applicable to a wider range of steels.

Question 41Magnetic Particle Testing (MT)

The residual magnetization technique can be used successfully only when the part:

  1. has been thoroughly demagnetized before inspection
  2. retains a usable leakage field after the current is removed Correct answer.
  3. is inspected with dry powder only
  4. is made of a nonferromagnetic alloy

Explanation

In the residual technique the magnetizing force is removed before particles are applied, so the part must be able to hold enough residual flux to attract particles at a discontinuity. Hard, high-retentivity steels are suitable; soft steels generally are not.

Question 42Magnetic Particle Testing (MT)

After inspection, a part is demagnetized mainly to:

  1. keep residual magnetism from affecting later machining or use Correct answer.
  2. permanently raise the magnetic permeability of the steel
  3. remove residual penetrant left in surface discontinuities
  4. restore the original heat treatment of the part

Explanation

Residual magnetism can attract chips and grit, deflect welding arcs, interfere with instruments, and disrupt later machining operations. Demagnetization reduces the residual field to an acceptably low level.

Question 43Magnetic Particle Testing (MT)

An AC electromagnetic yoke used for portable inspection must be capable of lifting:

  1. 22.5 kg (50 lb) at maximum pole spacing
  2. 1.5 kg (3 lb) at maximum pole spacing
  3. 4.5 kg (10 lb) at maximum pole spacing Correct answer.
  4. 4.5 kg (10 lb) with the poles touching each other

Explanation

Field adequacy for a yoke is verified by a weight-lifting test performed with the poles set at the maximum spacing that will be used in inspection. For an AC yoke the required lifting force is 4.5 kg (10 lb).

Question 44Magnetic Particle Testing (MT)

When prods are used to magnetize a part, the contact tips should normally be spaced:

  1. 13 to 25 mm (1/2 to 1 in) apart
  2. 75 to 200 mm (3 to 8 in) apart Correct answer.
  3. as widely as the part dimensions allow
  4. 250 to 300 mm (10 to 12 in) apart

Explanation

A prod spacing of roughly 75 to 200 mm (3 to 8 in) gives a field of useful strength and direction between the contacts. Tips should also be kept at least about 25 mm from edges to avoid poor field patterns near the part boundary.

Question 45Magnetic Particle Testing (MT)

For coil magnetization, the required ampere-turns are given by NI = 45,000/(L/D). For a part with an L/D ratio of 10, how many ampere-turns are needed?

  1. 4,500 Correct answer.
  2. 45,000
  3. 450
  4. 450,000

Explanation

Substituting L/D = 10 into the relation gives 45,000 divided by 10, or 4,500 ampere-turns. The L/D ratio is normally held between 2 and 15 when this formula is applied.

Question 46Magnetic Particle Testing (MT)

A one-inch-diameter steel bar is to be circularly magnetized with a head shot. What current range is typically used?

  1. 1000 to 2000 A
  2. 100 to 200 A
  3. 30 to 80 A
  4. 300 to 800 A Correct answer.

Explanation

For direct current passed through a steel part, a rule of thumb of 300 to 800 A per inch of diameter is used to produce an adequate circular field. The lower end is used where the part is easily magnetized and the higher end for less permeable steels.

Question 47Magnetic Particle Testing (MT)

Loose scale, oil, and dirt must be removed before magnetic particle inspection because they:

  1. can mask discontinuities and hold particles off the surface Correct answer.
  2. make the material nonmagnetic in the affected region
  3. permanently increase the retentivity of the part
  4. reduce the electrical resistance of the part being inspected

Explanation

Contaminants can bridge a discontinuity, prevent particles from reaching the leakage field, and create misleading background indications. A clean surface is required so particle mobility and contrast are not compromised.

Question 48Magnetic Particle Testing (MT)

A settling test of a wet fluorescent magnetic particle bath should show a settled particle volume of:

  1. 1.2 to 2.4 mL per 100 mL
  2. 0.1 to 0.4 mL per 100 mL Correct answer.
  3. 5 to 10 mL per 100 mL
  4. 0.01 to 0.05 mL per 100 mL

Explanation

Fluorescent baths are maintained at a lower particle concentration than visible baths, typically 0.1 to 0.4 mL settled volume per 100 mL. Fluorescent particles are highly visible, so low concentrations give good indications without heavy background.

Question 49Magnetic Particle Testing (MT)

An indication that appears at a sharp corner or abrupt change in cross section is best classified as:

  1. a relevant indication that requires rejection of the part
  2. a nonrelevant indication caused by part geometry Correct answer.
  3. a false indication produced by a permanent magnet
  4. a spurious indication caused by contaminated bath

Explanation

Abrupt geometry changes concentrate flux and cause leakage that attracts particles even though no discontinuity exists. Such geometry indications are nonrelevant and can usually be resolved by remagnetizing in another direction or by visual verification of the contour.

Question 50Magnetic Particle Testing (MT)

Dragging a permanent magnet across a part can leave a pattern resembling a crack. This pattern is:

  1. a nonrelevant indication caused by the part geometry
  2. a true discontinuity indication that requires repair of the part
  3. a false indication cleared by demagnetizing and re-inspecting Correct answer.
  4. a sign that the particle bath concentration is too high

Explanation

Local magnetization from contact with a magnet produces flux leakage unrelated to any discontinuity, known as magnetic writing. It is a false indication that disappears once the part is demagnetized and properly re-examined.