Magnetic Particle Level II: 15 Practice Questions, Answered From the Code

How to use these fifteen questions

Each question below states the question, the correct answer, and the reasoning that makes it correct. Work the reasoning, not the answer key. A Level II exam rewards the technician who can explain why 90 amp/in. applies to a half-inch plate and 100 amp/in. does not, because that same reasoning is what you use on a job where no code number is printed on the wall. Read the question, commit to an answer before reading on, then check whether your reason matches the code's reason. A right answer for the wrong reason fails the next question.

The clause numbers cited are ASME Boiler and Pressure Vessel Code Section V, Article 7, 2019 Edition and later. Article 7 was retitled Magnetic Particle Testing in that edition, the term black light became UV-A light throughout, paragraphs were added for LED sources, and the lux conversions were corrected. Where an employer's written practice still runs on an earlier edition, the values below hold except for the yoke check frequency, which is flagged in its own question. Our Section V compliance page sets out which article governs which method.

These are original questions written against the published body of knowledge for magnetic particle Level II. None is reproduced from any examination. If you are working toward certification rather than refreshing, the hours behind the exam matter as much as the exam itself: training hours by method sets out what MT Level II requires, and OJT hour logs covers the documentation an auditor will ask to see.

Magnetisation methods: matching the technique to the part

Question 1. A half-inch thick carbon steel plate is examined with prods set 6 in. apart. What magnetising current does Article 7 require? Answer: between 540 and 660 amperes, being 90 to 110 amp/in. of prod spacing multiplied by 6 in. Why: T-752 splits the current band by section thickness. Sections 3/4 in. (19 mm) and thicker take 100 to 125 amp/in. of prod spacing; sections thinner than 3/4 in. take 90 to 110 amp/in. A thin section presents less cross-section to the same current, so the surface field runs higher for the same amperage, and the heavy band would flood the surface with background particles.

Question 2. Why does Article 7 cap prod spacing at 8 in. and treat spacings under 3 in. as impractical? Answer: the field between the prods weakens as spacing grows, and at very close spacing the particles band around the tips. Why: current per inch of spacing is a proxy for field strength midway between the prods, which is the weakest point of the circular field the prods create. Beyond 8 in. (200 mm) that mid-span field falls below useful strength even at the top of the current band. Below roughly 3 in. (76 mm) the concentrated field at each tip holds particles in rings that mask real indications.

Question 3. A shaft 6 in. long and 4 in. in diameter is to be examined in an encircling coil. What does the code require? Answer: the coil technique cannot be used. Why: T-753 sets the coil requirement by length-to-diameter ratio, using 35,000/[(L/D)+2] ampere-turns at L/D of 4 or more and 45,000/(L/D) from L/D of 2 up to 4. At an L/D of 1.5 this shaft falls below the lower threshold, and Article 7 states that the coil technique cannot be used below L/D of 2. A short, thick part opposes the applied field with its own poles, collapsing the longitudinal field inside it. Ferromagnetic pole pieces added at each end raise the effective L/D.

Field direction versus discontinuity orientation

Question 4. A longitudinal crack runs along the axis of a pipe. Which magnetisation produces the strongest indication? Answer: circular magnetisation, achieved by passing current along the pipe axis or by threading a central conductor through the bore. Why: an indication forms only where flux crosses a discontinuity and leaks into the air above it. Flux running parallel to a crack passes through undisturbed and produces nothing at all. Circular magnetisation drives the field around the circumference, perpendicular to the axial crack, which is the orientation that maximises leakage. Direct-contact circular magnetisation runs at 300 to 800 amperes per inch of outer diameter.

Question 5. A technician yokes a weld with the legs across the toe, then repeats the pass with the legs rotated 45 degrees. Does this satisfy T-772? Answer: no. Why: T-772 requires the second field to be approximately perpendicular to the first, not merely different from it. With 45 degrees between the two passes, the worst-placed crack is the one bisecting them, and it presents only about 38 per cent of the flux as a crossing component in each pass. Rotate the second pass a full 90 degrees and that worst case rises to about 71 per cent. The perpendicular pair is the arrangement that maximises the weakest orientation, which is precisely what the clause protects.

Verifying that the field is adequate

Question 6. T-764 lists three ways to verify magnetic field adequacy and direction. Which one measures field strength? Answer: only the Hall-effect tangential-field probe used with a gaussmeter. Why: the pie-shaped field indicator and the artificial flaw shims are indicators, not instruments. They show that flux is crossing their artificial flaws and they show the direction of that flux, but neither returns a number. The Hall-effect probe placed against the surface reads the tangential field in gauss, which is the quantity governing particle mobility above a leakage site. ASTM E1444 places the working band for that tangential reading at roughly 30 to 60 gauss at the surface.

Question 7. A pie gage is placed on a machined surface during a yoke examination. Which way does the copper-plated face go? Answer: away from the examination surface, so the segmented steel face contacts the part. Why: the artificial flaws in a pie gage are the joints between its eight steel segments, and those joints sit on the face that touches the part. The copper plating on the opposite face is non-magnetic and provides a controlled gap that lifts the leakage field into the space where particles can gather and be seen. Invert the gage and the flux enters through copper, nothing leaks at the viewing face, and the tool reads blank whatever the true field.

Question 8. Why does Article 7 forbid a Hall-effect gaussmeter for verifying field adequacy with an encircling coil? Answer: the probe reads the coil's own field in air, not the useful field inside the part. Why: a tangential-field probe measures the field at the point where it sits. Inside and around an encircling coil that reading is dominated by the coil's air field, which is present whether or not the part is being magnetised usefully, so the number tells you about the coil rather than about the workpiece. T-753 therefore directs coil work to artificial flaw shims or a pie-shaped indicator, both of which respond to leakage flux generated by the part.

Yoke output and daily equipment checks

Question 9. An AC electromagnetic yoke and a permanent magnet yoke are both on the truck. What lifting power must each demonstrate, and at what spacing? Answer: 10 lb (4.5 kg) for the AC yoke and 40 lb (18 kg) for the permanent magnet yoke, each at the maximum pole spacing that will be used. Why: T-762 sets both values and ties them to the spacing actually worked at, because lifting power falls as the legs open. The direct-field yoke must lift four times as much because an alternating field concentrates near the surface through skin effect, while a steady field spreads through the full section, so far more total flux is needed to reach the same surface field.

Question 10. Your shop's procedure states that yoke lifting power is checked annually. Is that acceptable? Answer: not under the current code. Why: T-762 requires the magnetising power of yokes to be verified prior to use each day the yoke is used, and again whenever the yoke has been damaged or repaired. That frequency moved from annual to daily in the 2015 Edition of Section V, and procedures written before the change are among the most common findings on an MT audit. This is a document defect rather than a technician error, and it is fixed at the procedure level — see technical procedure development.

Wet versus dry, fluorescent versus visible

Question 11. What settling volumes does T-765 require for a wet bath, and how long do you wait before reading the tube? Answer: 0.1 to 0.4 mL of fluorescent particles or 1.2 to 2.4 mL of non-fluorescent particles per 100 mL sample, read after 60 minutes settling in a petroleum distillate carrier or 30 minutes in a water-based carrier. Why: the reading is a volume of settled solids in an ASTM D96 pear-shaped centrifuge tube. Read the stem early and the solids have not finished dropping, so a correctly loaded bath reads lean and gets over-dosed. Fluorescent particles carry far more visible signal each, which is why their band sits an order of magnitude lower.

Question 12. On a hot, freshly welded carbon steel joint in the field, what argues for dry powder over a wet bath? Answer: dry particles tolerate the surface heat and the rough as-welded profile, and they need no liquid carrier that would flash off. Why: a wet bath depends on its carrier to deliver particle mobility, and on a hot surface the carrier evaporates before particles can migrate to a leakage field. Dry particles take their mobility from the applied field and from gentle air, and they bridge weld ripple better than a film of suspension that pools in the valleys. A wet bath wins on fine, tight, surface-breaking cracks in smooth machined parts.

Light levels and viewing conditions

Question 13. A visible red-on-white MT examination runs in a fabrication bay. What light level must be present, and how is it established? Answer: a minimum of 100 fc (1076 lx) at the examination surface, measured with a white light meter before the examination, or established by using a verified light source. Why: T-777.1 sets the value and permits either route. Verification of a light source is demonstrated one time, documented and kept on file, which is why shops standardise on one lamp at one working distance rather than re-proving it daily. The meter itself is calibrated at least once a year under T-763, and whenever it has been repaired.

Question 14. Three numbers govern a fluorescent MT examination. What are they? Answer: UV-A of at least 1000 µW/cm² at the surface, ambient white light of no more than 2 fc (21.5 lx) in the darkened area, and a minimum of 5 minutes of dark adaptation before interpreting. Why: the first sets excitation, the second protects contrast, and the third conditions the eye. A fluorescent indication is read as a bright mark against near-black, so every footcandle of stray white light raises the background floor and destroys the ratio that makes a faint indication visible. Dark adaptation costs nothing and is skipped more often than any other requirement in the article.

Demagnetisation and closing out the examination

Question 15. When does Article 7 require a part to be demagnetised, and what residual level does it specify? Answer: whenever residual magnetism could interfere with subsequent processing or with the part's service use. The article sets no numeric residual limit. Why: the code frames the trigger as an engineering condition rather than a number, because the tolerable residual depends entirely on what happens next. A residual field pulls swarf onto machined surfaces, deflects the arc during subsequent welding, and disturbs instrumentation. The numeric limit comes from the referencing code section, the purchaser or the fabrication specification, and 3 gauss is a common contract value. Write the applicable figure into the procedure rather than inferring one.

Demagnetisation works by driving the material around progressively smaller hysteresis loops: apply a field at least as strong as the one that magnetised the part, then reverse and reduce it repeatedly. Withdrawing a part from an AC coil does this automatically at line frequency, since each cycle reverses the field while the falling coupling reduces its amplitude. DC demagnetisation steps current down through deliberate reversals. Coercivity decides how hard the part resists, which is why hardened and high-carbon components need more cycles than annealed low-carbon steel, and why a heat-treated shaft can hold field that a plate would not.

Where MT Level II candidates actually lose marks

The pattern across re-tests is consistent. Candidates lose marks on the two-direction rule, on lighting values borrowed from another method, and on equipment-check frequencies carried over from a superseded edition. None of those are physics failures; they are reading failures. The fix is to work through Article 7 once with the paragraph numbers in front of you, then answer questions from the clause structure rather than from a remembered number. Knowing that T-777 holds all the lighting values is worth more on exam day than knowing any single figure inside it.

The second pattern is field verification. A pie gage indicates direction and gross adequacy; it does not measure. A candidate who treats it as a measurement gets three linked questions wrong instead of one, because the same misunderstanding drives the shim question and the coil question. Fix the concept and the whole block resolves: shims and pie gages respond to leakage flux from artificial flaws, the Hall-effect probe returns a number, and the coil case removes the probe from the list because its reading belongs to the coil.

If you are preparing formally rather than revising, MT training covers the classroom hours, and our USA schedule covers where those hours run. Companies certifying a whole crew at once use corporate NDT training. Where the shortfall is a written practice or an approved procedure rather than a technician, that is ASNT Level III consulting work, and it is usually faster to fix than a failed certification cycle.

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