Nondestructive Testing for Aerospace Parts
Aerospace NDT is specified by method practice documents such as ASTM E1417 for penetrant, ASTM E1444 for magnetic particle, AMS-STD-2154 or ASTM E2375 for ultrasonic and ASTM E1742 for radiography, with acceptance criteria coming from the drawing or the program. The people doing the work are qualified to NAS 410, and the facility is usually Nadcap accredited.
Practice documents do not set acceptance
The single most common NDT mistake on a drawing is assuming the method standard tells the inspector what to reject. It usually does not. ASTM E1742, for example, states that its requirements control the quality of radiographic images and are not intended to set acceptance criteria for parts. Acceptance has to come from the engineering drawing, a material specification, a customer process spec or a program document.
A usable NDT note therefore has three parts: the method and practice document, the sensitivity or class, and the acceptance criteria. For example: fluorescent penetrant inspect per ASTM E1417, Type I, Method D, Sensitivity Level 3, acceptance per drawing note 7. Or: ultrasonic inspect per AMS-STD-2154, Class A. When the class itself embeds acceptance limits, as the ultrasonic classes do, name the class.
Method selection at a glance
| Method | Finds | Works on | Common practice document | Limits |
|---|---|---|---|---|
| Penetrant (PT) | Surface breaking cracks, porosity, laps | Nonporous metals and some plastics | ASTM E1417, materials to AMS 2644 | Surface only. Smeared metal from machining can close cracks |
| Magnetic particle (MT) | Surface and slightly subsurface discontinuities | Ferromagnetic material only | ASTM E1444 | Not for austenitic stainless, aluminum, titanium or nickel alloys |
| Ultrasonic (UT) | Internal discontinuities, laminations, bond lines | Wrought metals, composites, welds | AMS-STD-2154, ASTM E2375 (0.250 in and thicker) | Geometry and surface condition limit coverage |
| Radiography (RT) | Volumetric porosity, inclusions, shrinkage | Castings, welds, assemblies | ASTM E1742 | Tight planar cracks oriented badly to the beam can be missed |
| Eddy current (ET) | Surface cracks, conductivity, coating thickness | Conductive materials | Customer or program procedure | Shallow penetration. Needs reference standards |
| Computed tomography (CT) | 3D internal geometry and porosity | Additive parts, castings, small assemblies | Program specific | Resolution falls as part size grows |
Penetrant: type, method, sensitivity
Penetrant is the workhorse surface method for nonferrous aerospace parts. The classification comes from AMS 2644 and is used in ASTM E1417:
- Type: Type I fluorescent, viewed under UV-A. Type II visible dye, viewed in white light.
- Method: A water washable, B lipophilic post emulsifiable, C solvent removable, D hydrophilic post emulsifiable.
- Sensitivity: for fluorescent penetrants only, Level 1/2 very low, 1 low, 2 medium, 3 high and 4 ultrahigh. Levels are assigned by the Air Force Research Laboratory after testing manufacturer samples.
Higher sensitivity is not automatically better. Higher levels give stronger background fluorescence, which can mask real indications on rough surfaces such as castings. The governing procedure should choose the combination for the surface and the flaw of interest.
Machined surfaces in soft alloys often need etching before penetrant because machining smears metal over crack openings. Etch is itself a controlled chemical process, so if your part is a critical rotating or fracture critical component, check whether your program requires pre-penetrant etch and say so on the PO.
Magnetic particle
ASTM E1444 sets minimum requirements for magnetic particle testing of ferromagnetic material for aerospace, using the wet fluorescent method. It finds surface and slightly subsurface discontinuities and is the usual choice for 4130, 4340, 300M and martensitic or PH stainless parts. It does not work on austenitic stainless steel. A recent revision is listed as E1444/E1444M-25 or later, so confirm the revision your procedure cites.
Parts must be demagnetized after inspection, and residual field limits belong in the procedure. Plated or painted parts are normally inspected before finishing, which affects routing. Put MT before final finish on the router.
Ultrasonic and radiography
Ultrasonic inspection of wrought product is done to AMS-STD-2154 or ASTM E2375. ASTM E2375 was adopted to replace MIL-STD-2154, covers wrought products 0.250 in (6.35 mm) thick or greater, defines five acceptance classes in its Table 1, and sends aluminum product to ASTM B594. Raw material is often bought already UT inspected to a class, which is cheaper than inspecting a finished part where fillets and thin webs limit coverage.
Radiography to ASTM E1742 is the standard for castings and welds. Remember that E1742 controls image quality only. Weld acceptance comes from AWS D17.1 class tables or the program, and casting acceptance from the casting spec or a reference radiograph set named on the drawing. Digital radiography and CT are increasingly used for additive parts, where internal lattices and channels cannot be reached by any other method. See the metal additive page.
Eddy current in the shop
Eddy current is the quiet workhorse behind several checks engineers rarely think of as NDT: electrical conductivity screening of aluminum temper after heat treatment, coating thickness on anodize and paint, and crack detection around fastener holes. Each use needs reference standards made from the same alloy and condition as the part, so ask the source what standards it holds before assuming it can run your check.
Fracture critical hardware and POD
For NASA flight hardware under fracture control, NDE requirements come from NASA-STD-5009, revision C (2023), which applies where fracture control and a quantitative probability of detection (POD) demonstration are required, and supports the fracture control requirements in NASA-STD-5019A. The practical consequence: standard NDE assumes a certain detectable flaw size only when the method, procedure and personnel meet the standard. If a fracture analysis assumes a smaller initial flaw, special NDE with its own POD demonstration is needed.
Tell your supplier early if a part is fracture critical. It changes the inspection method, the surface condition required before inspection, the personnel level and the record retention.
NAS 410: who is allowed to inspect
NAS 410, maintained by the Aerospace Industries Association, sets qualification and certification for aerospace NDT personnel. The AIA does not certify anyone. Each employer runs a written practice, trains and examines its people, and certifies them per method.
| Level | What they may do |
|---|---|
| Trainee | Works under direct supervision of Level 2 or 3. Cannot independently accept parts |
| Level 1 | Performs inspections and simple calibrations to written instructions |
| Level 2 | Sets up, calibrates, inspects, interprets and accepts or rejects to procedure without supervision |
| Level 3 | Writes and approves procedures and techniques, administers exams, runs the NDT program |
Training and experience hours differ by method and level, and published figures vary between training providers. Certification lapses after five years unless renewed by re-examination or evidence of continued satisfactory performance. When auditing a source, ask for the written practice and the certification records of the people who will sign your parts.
Accreditation and records
Nadcap accredits NDT facilities under the AC7114 criteria, with separate checklists for penetrant, magnetic particle, ultrasonic and film radiography among others. Many primes require Nadcap NDT plus their own approval for each method. An NDT cert should identify the part, the method and practice document with revision, the technique or procedure number, the sensitivity or class, the acceptance criteria, results, and the inspector name, level and certification. For how NDT records fit into a first article report, see inspection and metrology.
Get NDT sourced and documented
If you need penetrant, mag particle, ultrasonic, radiographic, eddy current or CT inspection on parts or raw stock, send the part and acceptance requirements. We match the work to qualified inspection sources, flow down the method, class and personnel requirements, check the reports before release, and a person replies within one business day. Mutual NDA before files. For export controlled data, see controlled programs. Related: processes hub, sheet metal and welding, heat treatment.
Questions
Does ASTM E1417 tell the inspector what to reject?
No. ASTM E1417 is a practice for performing penetrant inspection: process controls, materials, sensitivity and in-use checks. Acceptance criteria must come from the drawing, a material or process specification, or a program document. The same is true for radiography under ASTM E1742, which explicitly controls image quality only. Always pair the practice document with a stated acceptance standard on the drawing or PO.
Which penetrant sensitivity level should I specify?
Choose by surface condition and the flaw size of concern rather than defaulting to the highest level. AMS 2644 defines Levels 1/2, 1, 2, 3 and 4 for fluorescent penetrants. Higher levels detect finer indications but raise background fluorescence, which can hide real indications on rough castings. In practice your program or customer process specification usually dictates the level, so check it before choosing one yourself.
Can magnetic particle be used on stainless steel?
Only on ferromagnetic grades. Martensitic and precipitation hardening stainless steels such as 410, 15-5PH and 17-4PH can be inspected with magnetic particle per ASTM E1444. Austenitic grades such as 304, 316 and A286 are not ferromagnetic, so they are inspected with penetrant or eddy current instead. The same applies to aluminum, titanium and nickel alloys.
What is the difference between AMS-STD-2154 and ASTM E2375?
Both cover ultrasonic inspection of wrought metal products and trace back to MIL-STD-2154. ASTM E2375 states that it was adopted to replace that military standard and covers product 0.250 in thick or greater, with five acceptance classes in its Table 1. AMS-STD-2154 is the SAE document used on many aerospace drawings. Use whichever your drawing or material spec names.
What NAS 410 level should sign my parts?
Acceptance decisions are normally made by a Level 2 or Level 3 certified in that specific method. Level 1 personnel may perform inspections to written instructions, and trainees work only under supervision. Ask the source for the certification record of the person who will accept your parts, and confirm the certification is current, since NAS 410 certifications must be renewed every five years.
When is NASA-STD-5009 involved?
When a NASA program applies fracture control and needs a quantitative probability of detection for a flaw size. NASA-STD-5009 sets NDE requirements for fracture critical metallic components, flight or ground, and supports NASA-STD-5019A. If your part is fracture critical, tell the supplier before quoting, because special NDE, surface preparation and personnel requirements can change cost and lead time.
Related
Sources
- ASTM E1742/E1742M-23 radiographic examination
- ASTM E2375 ultrasonic testing of wrought products
- SAE AMS-STD-2154 ultrasonic inspection of wrought metals
- ASTM E1444/E1444M magnetic particle testing for aerospace
- Magnaflux: guide to AMS 2644 penetrant sensitivity levels
- Open Exam Prep: penetrant types, methods and sensitivity
- NASA Technical Standards: NASA-STD-5009 NDE for fracture critical components
- ATS: NAS 410 training and levels
- AviationPros: NDT certification under NAS 410
- Performance Review Institute: Nadcap
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