When should a drawing call for dye penetrant inspection or magnetic particle testing on castings and weldments, and what acceptance criteria apply?

How do you know a delivered part needs a surface NDT callout?

If cracks, cold shuts, laps or open porosity are being found at your receiving inspection, at assembly, under a pressure test or in the field, and the drawing has no surface examination requirement, the supplier had no obligation to look for them.

The typical signs are hairline cracks at fillets, junctions and weld toes that show up only after paint or plating fails; pinholes on a machined sealing face; a lap or cold shut that opens under load; or a crack that a customer found with their own penetrant kit. Visual inspection catches the coarse defects, but fine, tight cracks are often invisible to the eye on an as-cast or as-welded surface. TWI describes penetrant examination as a very sensitive method, capable of finding extremely fine flaws, provided the surface is properly cleaned and prepared first (TWI, advantages and disadvantages of penetrant examination).

Before you add a callout, confirm that the defect really is surface-connected. Internal shrinkage or gas porosity that only appears after a cut is a different problem with different tools: see the guide on porosity that appears after machining and the X-ray grading guide.

For the lot already on your bench, work through it in this order before you rewrite the drawing:

1. Quarantine and count. Tag the suspect lot, record how many parts show the defect and where on the part it sits, and photograph each indication next to a scale.
2. Confirm it is surface-breaking. Re-examine the suspect zones with penetrant (or MT on ferromagnetic steel) after cleaning off paint, oil and plating residue; a coating left in place can hide the opening. If an MT indication may be spurious, for example at a change in magnetic properties or a dissimilar-metal joint, TWI suggests dressing the surface and confirming with penetrant (TWI Job Knowledge, NDE part 1).
3. Classify the indication. Note whether each one is linear (crack, cold shut, lap) or rounded (pore), its length, and whether it sits at a fillet, a weld toe, a machined face or an as-cast skin. Location usually points to the source: casting, welding, heat treatment or a later machining or grinding step.
4. Agree the rule before sorting. Write the acceptance limit you will sort to, per zone, and get the supplier to accept it in writing; without it, every reject is a negotiation.

Should the drawing call for dye penetrant or magnetic particle testing?

Call for magnetic particle testing on ferromagnetic steels and irons when you also care about defects just below the surface; call for penetrant testing on everything else, including aluminum, zinc, copper alloys and austenitic stainless steel.

Penetrant testing is limited to nonporous metal and nonmetal components and finds only discontinuities open or connected to the surface (ASTM E1417/E1417M-21e1). Magnetic particle testing detects surface or slightly subsurface discontinuities in ferromagnetic material (ASTM E3024/E3024M-22a). For aerospace work the MT practice is ASTM E1444/E1444M, which is written around the wet fluorescent method; general industry uses E3024/E3024M (ASTM E1444/E1444M-26). Use the table as a first screen.

Two details decide many cases. First, MT is sensitive to orientation: a flaw shows best when it cuts the magnetic flux at 90°, so TWI advises generating fields in two directions at 90° to one another; flaws at up to 45° from that ideal are still accepted as shown (TWI, defects of all orientations). Second, the subsurface reach of MT is shallow; TWI puts it at up to perhaps 1 mm below the surface for rectified half-wave DC prods, depending on flaw size and orientation (TWI Job Knowledge, NDE part 1). Anything deeper needs radiography or ultrasonic testing.

Within penetrant testing, the drawing can also fix the sensitivity. Fluorescent penetrant gives greater sensitivity than visible (red) dye, per the same TWI article, so critical zones are typically called out with a fluorescent system and cosmetic or non-critical areas with visible dye.

How should a PT or MT callout be written on the drawing or RFQ?

A complete callout names the method and practice, the technique or sensitivity, the zones, the stage in the routing, the acceptance standard and level for each zone, the sampling, and the records and personnel qualification.

A note built that way can be quoted, performed and disputed on the same terms. An illustration of the format, not a recommendation for any particular part:

• Method: fluorescent penetrant per ASTM E1417/E1417M in Zone A; visible dye permitted in Zone B. (For a carbon-steel weldment: wet fluorescent MT per ASTM E3024/E3024M, two directions at right angles.)
• Zones: Zone A = sealing face, O-ring groove and fillets marked on sheet 2; Zone B = remaining machined surfaces; as-cast surfaces outside A and B visual only.
• Stage: final examination after machining and heat treatment, before any coating, plating or impregnation; etch machined soft-alloy surfaces before PT.
• Acceptance: per ASTM A903/A903M at the level stated for each zone, or for non-ferrous castings the indication limits written on the drawing using ASTM E433 terms; for welds, ISO 23277 or ISO 23278 at the stated acceptance level, or the governing code.
• Sampling: stated in the PO, with heavier sampling at first article and after any process change.
• After examination: remove residues; demagnetize after MT if the part goes near sensors, bearings or machining.
• Records and people: report per lot with procedure, materials, zone results and the inspector’s qualification under ISO 9712 or the employer’s written practice to ASNT SNT-TC-1A.

Before release, run this buyer checklist against the drawing: is the material ferromagnetic (if not, delete MT)? Are zones drawn, not only described? Is the stage named relative to machining and coatings? Does every zone have an acceptance level, not just a test standard? Is a repair or rework rule stated, such as whether a cracked casting may be weld-repaired and re-examined? Personnel qualification is covered by ISO 9712:2021; the first article guide covers how the NDT report fits into the wider FAI package.

Who does what on a Saola order when the drawing calls for PT or MT?

CNC turning, milling and welding are done at our lead CNC plant, T.K Viet Nam Precision Company Limited in Vietnam; die castings, sand castings and all surface finishing come from partner plants we manage. Each quote names the production site and the country of origin, and states who performs any penetrant or magnetic particle examination.

We do not claim our own NDT laboratory. When a drawing calls for PT or MT, the examination is arranged with the casting partner or with an independent testing laboratory, and we confirm before quoting which practice, technique and acceptance standard the examiner will apply and what qualification the inspector holds. Machining is planned so the final examination happens after the cuts that could open or smear a crack, and before the part goes to finishing. Parts are machined by CNC milling or CNC turning; the die casting and sand casting pages describe the partner-plant programs. If machining opens a crack, the aim is to photograph it, mark its location on the drawing and report it to you before the lot moves on. ISO 9001 certification is in progress, not held; the quality page lists the records issued today. Send the drawing with zones, method and acceptance levels marked through the quote form.