6.4 Quality Control of MT Equipment and Processes

Quality Control of Equipment Processes is official MT general topic 10 on the outline administered prior to 15 December 2026. It is the heading that turns yesterday's good yoke into today's invalid exam. Process control asks a blunt question: can this equipment, this bath, and this light still show a known discontinuity? If the answer is not demonstrated, production interpretations are guesses.

ASTM E1444, ASTM E709, and ASME Section V, Article 7 are again the industry sources for the numbers in this section. ASNT does not publish a secret lift weight or a secret centrifuge band. Attribute the value to the standard, then obey the procedure if it is tighter.

After 15 December 2026, ASNT's revised five-domain MT outline — principles and theory; use and care of equipment; techniques; interpret, evaluate, and document; and codes and procedures — calls out daily standardizations in plainer language: yoke lift checks at the familiar 10 lb / 40 lb levels, Ketos-type system pieces, and QQI shims. That is not a new method. It is the same process control this section already teaches. Keep the current ten-topic outline as your study baseline; treat the December 2026 wording as a reminder that daily checks are exam-visible.

Daily yoke lift test

An electromagnetic yoke is verified by lifting a certified dead weight with the legs in the working pole spacing.

Perform the lift daily, or at the start of each shift if the procedure says so, and after any event that could change output (dropped yoke, repaired cord, suspected overheating). Legs must be on the weight, not on a steel table that shares the flux path. Articulating legs are set to the spacing you will use on the work. A yoke that lifts 10 lb at 2 in (50 mm) spacing and then is opened to 8 in (200 mm) on a pipe is no longer the yoke you certified.

AC versus DC matters. Do not certify an AC yoke with a 40 lb weight and call it done. Do not certify a DC yoke with a 10 lb weight and assume extra margin. Permanent-magnet yokes have their own lift values in the procedure and the applicable standard; they still get a documented lift, because magnets fade, pole faces wear, and temperature changes output.

A failed lift removes the yoke from service until it is repaired and rechecked. Production work done after a failed, skipped, or unrecorded lift is not a valid Article 7 / E1444 examination.

Ketos ring and AS 5282 system performance

A Ketos ring is a tool-steel ring with side-drilled holes at several depths. Current is passed through a central conductor; particles should show a specified number of holes. SAE AS 5282 is the aerospace standard that defines a controlled ring of this type. Shops say "Ketos" the way they say "QQI" — as a system performance tool, not as a production part.

What the ring proves:

• The power supply can deliver the intended current.
• The ammeter is not wildly wrong.
• The particles can still move and fluoresce or contrast.
• Lighting is adequate to see a known subsurface-leaning hole pattern.

What the ring does not prove:

• That a production weld's acceptance table was met.
• That field direction on a complex geometry was correct (that is closer to a QQI job).
• That a yoke on a girder is adequate (use the lift test and, when required, a QQI on the work).

Run the ring on the interval the procedure requires — often daily or each shift on a wet bench. Record current, media, and which holes appeared. If fewer holes appear than the procedure demands, stop production and find the cause (weak bath, wrong current, bad light, contaminated particles).

QQI shims

A quantitative quality indicator (QQI) is a thin shim with etched artificial discontinuities (circles, crosses, or similar). You tape or fixture the shim on the part, apply the production magnetization and media, and confirm that the etched pattern appears in the intended orientation.

QQIs answer questions the Ketos ring cannot:

• Is the field direction crossing the discontinuity I care about?
• Is the field adequate at this geometry, not merely at a ring on the bench?
• Did a multidirectional or swinging-field shot actually produce a usable vector?

Place the QQI in the least-favorable location the procedure names — a thick section, a pole-spacing extreme, a coil dead zone. A beautiful QQI on the bench table and a dead field on the far side of a nozzle is a failed control. QQIs do not replace the acceptance standard on real discontinuities. They qualify the shot.

Wet-bath settling test (pear-shaped centrifuge)

Wet particle concentration is checked with a pear-shaped centrifuge tube. A 100 mL sample of agitated bath settles for the time the procedure and ASTM E1444 specify, and the Level II reads the packed-particle volume.

Typical ASTM E1444 ranges (industry practice — the procedure wins if it states another band):

Low concentration misses tight cracks. High concentration paints the part with background and hides indications. Fluorescent baths run much leaner than visible baths; a fluorescent reading of 2 mL is not "extra sensitive," it is usually a contaminated or over-charged bath.

Take the sample from the agitated bath at the point of application, not from a stagnant corner. Allow the specified settle time — rushing the reading under-reports solids. Check water and oil baths on their own schedules; do not use a water-bath number on an oil system without the procedure's permission.

The centrifuge volume is necessary and not sufficient. Look at the settled solids and the supernatant:

• Dirt, rust, and sand raise the volume without adding useful magnetic particles.
• Scum, oil in a water bath, or water in an oil bath ruins wetting and fluorescence.
• Lost fluorescence (particles still settle, but they are dull under UV-A) means the pigment is spent.
• Foam from excess conditioner changes application.

If the bath looks wrong, dump and recharge even when the millilitre reading is in band.

Lighting checks and UV-meter calibration

Process control includes the numbers from section 6.1, measured again as a check, not remembered from last month.

• Fluorescent work: UV-A ≥ 1000 μW/cm² at the surface and ambient visible often ≤ 20 lux (2 fc), per the usual ASTM E1444 / E709 / ASME V Article 7 values, or the procedure's tighter limits.
• Visible-particle work: white light commonly ≥ 1000 lux (100 fc) at the surface.

Check lamps daily or each shift: warm-up (if required), filter condition, cracked lenses, LED failure of individual emitters, and actual meter readings at the working distance. A lamp that passed last Tuesday and was dropped this morning is unverified.

The UV-A radiometer and the visible-light meter are themselves calibrated on the interval the procedure and the meter manufacturer require. A meter that drifted high will bless a dim booth. Record meter serial numbers and due dates the same way you record yoke identity. ASNT does not publish a universal calibration interval; do not invent one on the exam. The correct answer is the procedure / manufacturer interval.

Ammeter checks

Bench and power-pack ammeters tell you whether the circular or coil shot met the procedure. Compare the unit's meter to a calibrated shunt, standard meter, or known load on the interval the procedure requires, and whenever the reading disagrees with a system-performance piece (Ketos holes disappear at a current that used to show them). Cables, connections, and dirty contacts can drop true current while a sticky meter still paints a comforting number. Prod work is especially sensitive: the exam wants amperage as a function of spacing, not "about half a turn on the dial."

Contamination and media condition

Treat contamination as a daily visual and functional check, not as housekeeping.

• Dry powder that has picked up moisture clumps and will not fly.
• Dry powder mixed with grinding dust is no longer a controlled particle size.
• Fluorescent wet baths collect oil, paper, and faded pigment.
• Visible wet baths collect rust from unprotected tanks.
• Mixing leftover water-conditioned powder into an oil carrier — or the reverse — breaks suspension and wetting.

If in doubt, replace the media. Media cost less than a missed quench crack.

A practical daily / shift sequence

The exact sequence belongs to the procedure. A Level II who can recite a complete, attributed set will not freeze on topic 10:

1. Identify equipment and confirm calibration due dates (meters, ammeters, weights).
2. Yoke lift: AC 10 lb (4.5 kg) or DC 40 lb (18 kg) as applicable (ASTM E1444 / E709 / ASME V Article 7).
3. Lighting: UV-A and ambient, or white light, at the surface.
4. Bath: centrifuge volume in the ASTM-typical or procedure band; visual contamination check.
5. System performance: Ketos / AS 5282 on the bench circuit; QQI on the geometry when the procedure requires a field-adequacy check.
6. Record the results before the first production part.
7. Remove failed equipment from service.

Realistic exam scenarios

An AC yoke lifts 8 lb (3.6 kg) at the working spacing. The Level II must stop. There is no "close enough" to the 10 lb industry value, and there is no extra particle dusting that restores magnetizing force.

A fluorescent centrifuge reads 0.05 mL / 100 mL. Sensitivity is below the usual 0.1–0.4 mL ASTM E1444 band. Recharge or concentrate per the procedure, then recheck, before the next shaft hits the booth.

A Ketos ring shows fewer holes than yesterday at the same indicated amperage. The problem may be the bath, the light, the ammeter, or the cables. System performance failed; production interpretations wait.

A candidate testing after 15 December 2026 sees a stem about "daily standardizations" that names 10 lb, 40 lb, Ketos, and QQIs. That is the revised outline's language for the controls this section already treats as routine under ASTM E1444, ASTM E709, and ASME Section V, Article 7. It is not permission to abandon the rest of the current ten-topic study map — principles, flux fields, current, method selection, and demagnetization still matter. It is a reminder that process control is how a Level II proves the rest of the method is real today.