Non-Destructive Testing Glossary
A
AMS (Aerospace Material Specification)
A technical standard published by SAE International that defines material composition, processing, and quality requirements for aerospace components, including the NDT methods and acceptance criteria a part must meet. American Metal Testing performs inspections to AMS callouts as specified by the customer or design engineer. See: Aerospace.
ANSI (American National Standards Institute)
A nonprofit organization that oversees the development of voluntary consensus standards for products, services, and processes in the United States. NDT specifications referencing ANSI standards are among the regulations AMT routinely works to. See: Non-Destructive Testing.
ASME (American Society of Mechanical Engineers)
A professional engineering organization that publishes codes and standards covering mechanical components. ASME's Boiler and Pressure Vessel Code includes NDT requirements that AMT supports for customers in relevant industries.
ASTM (American Society for Testing and Materials)
An international standards organization, now known as ASTM International, that develops technical standards for materials, products, and testing methods. ASTM specifications govern many of the inspection procedures, acceptance criteria, and reference standards used in fluorescent penetrant, magnetic particle, and radiographic testing. See: Testing Standards.
AWS (American Welding Society)
A professional association that develops codes and standards for welding, including inspection criteria for weld quality. AMT performs NDT on welded components to AWS specifications when called out by the customer.
C
Crack
A linear discontinuity caused by fracture, fatigue, or stress that breaks the continuity of a material's surface or internal structure. Cracks are among the most critical defect types identified through fluorescent penetrant, magnetic particle, and radiographic inspection, since they can propagate under load and lead to part failure.
D
Developer
A fine white powder or coating applied during fluorescent penetrant inspection that draws trapped penetrant back out of a surface discontinuity, amplifying the indication and improving contrast under ultraviolet light. See: Fluorescent Penetrant Inspection.
Discontinuity
An interruption in the normal physical structure of a material, such as a crack, void, or inclusion. Not every discontinuity is a rejectable defect; whether a discontinuity is acceptable depends on its size, location, and the quality standard the part is being inspected against. See: Non-Destructive Testing.
Dry Powder Method
A magnetic particle inspection technique in which dry, finely divided ferromagnetic particles are applied to a magnetized part. The particles cluster at locations where a surface or near-surface flaw disrupts the magnetic field, forming a visible indication. AMT offers both dry powder and wet fluorescent magnetic particle methods. See: Magnetic Particle Inspection.
Dwell Time
The period during fluorescent penetrant inspection in which the penetrant is left on the part surface to seep into any surface-breaking discontinuities before excess penetrant is removed. Dwell time varies by penetrant type, material, and the discontinuities being targeted.
E
Emulsifier
A chemical agent used during the excess removal step of fluorescent penetrant inspection to make oil-based penetrant water-washable. Emulsifiers allow inspectors to rinse surface penetrant away while leaving penetrant trapped within discontinuities undisturbed. See: Fluorescent Penetrant Inspection.
F
Ferromagnetic Material
A material, such as iron, nickel, cobalt, or their alloys, that can be strongly magnetized and is therefore suitable for magnetic particle inspection. Non-ferrous metals like aluminum and certain stainless steel grades cannot be tested with MPI and instead require a method such as fluorescent penetrant or radiographic inspection. See: Magnetic Particle Inspection.
FPI (Fluorescent Penetrant Inspection)
A non-destructive testing method that uses a fluorescent dye penetrant to reveal surface-breaking discontinuities, such as cracks, porosity, and inclusions, in non-porous metallic and non-metallic components. The penetrant is applied, allowed to dwell, then developed and inspected under ultraviolet light. AMT performs FPI as a NADCAP-accredited process for parts up to roughly 4-5 inches square or in diameter, 3-4 inches thick, and up to 10 pounds. See: Fluorescent Penetrant Inspection.
I
Inclusion
A foreign material, such as slag, oxide, or sand, trapped within a metal during casting or welding. Inclusions can weaken a part and are one of the discontinuity types that fluorescent penetrant, magnetic particle, and radiographic inspection are each capable of detecting, depending on whether the inclusion is at the surface or below it.
Indication
The visible evidence of a discontinuity produced during NDT examination, such as a bleed-out of fluorescent dye under UV light or a buildup of magnetic particles along a flaw. Not every indication corresponds to a rejectable defect; a certified inspector evaluates each indication against the applicable acceptance criteria to determine whether it is relevant.
L
Lack of Fusion
A weld discontinuity in which the weld metal fails to properly fuse with the base metal or with a previous weld pass. Lack of fusion is a subsurface flaw that radiographic inspection is used to detect, since it often cannot be identified through surface examination alone. See: Radiographic Inspection.
Liquid Penetrant Inspection
Another name for fluorescent penetrant inspection, referring to the liquid dye penetrant used to reveal surface discontinuities. AMT's liquid penetrant testing follows a five-step process: pre-cleaning, penetrant application, excess removal, inspection under UV-A light, and post-cleaning. See: Liquid Penetrant Inspection.
M
Magnetic Yoke
A handheld electromagnetic device used to induce a localized magnetic field in a ferromagnetic part during magnetic particle inspection. The yoke is one of two common magnetization methods, the other being passing electric current directly through the part.
Magnetization
The step in magnetic particle inspection in which a strong magnetic field is induced in a part, either by passing electric current through it or by applying a magnetic yoke to its surface. Surface and near-surface discontinuities distort this field, which causes magnetic particles to gather at the flaw location. See: Magnetic Particle Inspection.
Material Specification
A formal document, typically published by an organization such as ASTM or AMS, that defines the chemical composition, mechanical properties, and quality requirements a material or part must meet for a given application. Selecting the appropriate material specification is generally the responsibility of the design engineer, who understands the part's intended use; AMT then performs the inspection methods and procedures called out by that specification. See: Non-Destructive Testing.
MIL-SPEC (Military Specification)
A standard issued by the U.S. Department of Defense that establishes design, performance, and quality requirements for military hardware. AMT performs NDT to MIL-SPEC requirements for customers serving military and defense applications. See: Military and Defense.
MPI (Magnetic Particle Inspection)
A non-destructive testing method used to detect surface and near-surface discontinuities in ferromagnetic materials. A part is magnetized, then magnetic particles, applied as a dry powder or wet suspension, gather at locations where a flaw disrupts the magnetic field. MPI cannot be used on non-ferrous metals such as aluminum. AMT can inspect parts and components up to 12 feet long using this method. See: Magnetic Particle Inspection.
N
NADCAP (National Aerospace and Defense Contractors Accreditation Program)
An industry-managed accreditation program that audits and certifies special processes, including non-destructive testing, against aerospace and defense quality requirements. American Metal Testing is a NADCAP-accredited NDT laboratory, a credential that qualifies it to perform testing for aerospace manufacturers such as Boeing, Parker Aerospace, and UTC Aerospace Systems. See: Testing Standards.
NAS-410
An aerospace standard that defines the certification requirements for NDT personnel, covering training, experience, and examination requirements for inspectors at each qualification level. AMT's fluorescent penetrant, magnetic particle, and radiographic inspections are interpreted by NAS-410-certified inspectors. See: Testing Standards.
NDT (Non-Destructive Testing)
A category of inspection methods used to evaluate the properties of a material, component, or system without causing damage. NDT allows a part to be examined for surface and internal discontinuities while remaining fully usable afterward. AMT specializes in three NDT methods: fluorescent penetrant inspection, magnetic particle inspection, and radiographic inspection. See: Non-Destructive Testing.
P
Porosity
Small voids or gas pockets trapped within a metal during casting or welding. Porosity can reduce a part's mechanical strength and pressure integrity, and it is one of the most common discontinuities detected through fluorescent penetrant, magnetic particle, and radiographic inspection, depending on whether it occurs at the surface or beneath it.
Post-Cleaning
The final step in fluorescent penetrant and magnetic particle inspection, in which residual penetrant, developer, or magnetic particles are removed from a part after examination. Post-cleaning prepares the part for any subsequent processing or shipment. See: Fluorescent Penetrant Inspection.
Pre-Cleaning
The first step in most NDT processes, in which a part is cleaned and dried to remove oil, grease, dirt, paint, or other contaminants that could mask a discontinuity or interfere with the inspection. Thorough pre-cleaning is essential to producing accurate and repeatable results.
Q
Quality Level
The acceptance criteria a part must meet to be considered free of rejectable discontinuities, typically defined by the governing material specification and inspection procedure rather than chosen independently by the testing lab. Setting a quality level that exceeds what a part's application actually requires can drive up cost or make a part difficult or impossible to manufacture, which is why the specification is usually set by the design engineer with knowledge of the part's intended use. See: Non-Destructive Testing.
R
Radiograph
The film or digital image produced during radiographic inspection, showing the internal structure of a metal part as X-rays pass through it. Denser or thicker regions of the part absorb more radiation and appear lighter on the radiograph, while voids, cracks, and inclusions appear darker due to reduced absorption.
RI / RT (Radiographic Inspection)
A non-destructive testing method that uses X-rays to penetrate a metal component and reveal internal and subsurface discontinuities, such as cracks, voids, inclusions, and lack of fusion. Because it produces a permanent film record, radiographic inspection is often specified where documented traceability is required, or where internal integrity cannot be confirmed through surface methods alone. AMT performs NADCAP-certified radiographic testing for components up to 20 pounds, with thickness capacity varying by material. See: Radiographic Inspection.
S
SAE (Society of Automotive Engineers)
A professional association, now operating as SAE International, that develops engineering standards for the aerospace, automotive, and commercial vehicle industries, including AMS specifications that govern many NDT and material requirements. See: Testing Standards.
Subsurface Discontinuity
A flaw, such as a void, inclusion, or lack of fusion, that lies beneath the surface of a part and cannot be detected by surface inspection methods like fluorescent penetrant testing. Subsurface discontinuities generally require magnetic particle inspection, which can reveal near-surface flaws, or radiographic inspection, which can reveal flaws deeper within a part.
Surface Discontinuity
An irregularity, crack, or imperfection located at the surface of a part. Some surface discontinuities are visible to the naked eye, while others require fluorescent penetrant or magnetic particle inspection to detect. See: Non-Destructive Testing.
T
Traceability
The documented chain linking an inspection result back to a calibrated measurement standard. AMT's in-house equipment is calibrated and traceable to the National Institute of Standards and Technology (NIST), supporting the accuracy and defensibility of its test results. See: Testing Standards.
U
UV-A Light (Black Light)
Ultraviolet light in the A-band range, used during fluorescent penetrant inspection to cause the fluorescent dye trapped in a surface discontinuity to glow brightly against a darkened background. This contrast makes even very fine cracks or porosity visible to the inspector. See: Fluorescent Penetrant Inspection.
W
Weldment
An assembly of metal parts joined together by welding. Weldments are commonly inspected through magnetic particle testing for ferromagnetic materials or radiographic inspection for internal weld quality, since defects such as porosity and lack of fusion can compromise a weld's strength. See: Metal Fabrication Testing.
Wet Fluorescent Magnetic Particle Method
A magnetic particle inspection technique in which ferromagnetic particles are suspended in a liquid carrier and fluoresce under UV-A light, improving sensitivity to very fine surface and near-surface discontinuities compared to dry powder methods. AMT offers both wet fluorescent and dry powder MPI techniques. See: Magnetic Particle Inspection.
X
X-Ray Testing
A common name for radiographic inspection, referring to the X-rays used to penetrate a metal part and reveal its internal structure on film or digital media. See: Radiographic Inspection.
