ASNT VT Level III key terms

The sharpness of a person's eyesight, commonly measured as the smallest detail that can be distinguished at a standard distance; near acuity is typically checked at 12 to 16 inches for VT personnel.

An eye examination, often using a Jaeger or Snellen near card, that verifies a VT inspector can read small characters at a specified distance; required periodically under most qualification programs.

The ability to distinguish hues, verified by tests such as Ishihara plates; important because VT often relies on color differences between indications and background or between penetrant and developer.

The ability to detect differences in luminance between an indication and its background; low-contrast conditions make small or faint discontinuities much harder to see than high-contrast ones.

The eye's adjustment of its lens to focus on objects at different distances; prolonged close work can tire this mechanism and degrade inspection reliability.

The difference in brightness or color between an indication and the surrounding surface; higher contrast generally improves detectability of a discontinuity.

The amount of light falling on a surface, usually expressed in lux or foot-candles; specifications set minimum values for inspection, with higher values often required for small or critical features.

An instrument used to measure illuminance at the inspection surface so the examiner can confirm that lighting meets the procedure's minimum requirement.

Excessive or misdirected light that reduces visibility by overwhelming the eye; it can mask indications and should be controlled by positioning lamps and shielding.

The smallest separation at which two adjacent features can still be distinguished as separate; it limits the size of discontinuity a VT system can reliably detect.

The ratio by which an optical device enlarges the apparent size of an object; higher power narrows the field of view and reduces depth of field.

The range of object distances over which an optical system remains acceptably in focus; it decreases as magnification or aperture increases.

An optical instrument with a rigid or flexible tube used to view internal surfaces through small openings; rigid types give better image quality while flexible types reach convoluted paths.

A flexible viewing instrument that carries images through a bundle of optical fibers; individual fiber breakage appears as dark spots that can obscure or mimic indications.

Visual examination performed with cameras, borescopes, or video systems when the surface is inaccessible or unsafe for direct viewing; image quality and lighting must be verified.

Examination in which the inspector's eye views the surface without intervening optical or imaging devices, giving the best resolution and depth perception.

A technique in which light is passed through a translucent material and the far side is viewed, so discontinuities appear as shadows or bright spots.

Use of a mirror to view surfaces hidden from direct line of sight, such as inside tubes or behind obstructions; image quality depends on mirror flatness and cleanliness.

A visual response from a surface that may or may not be a true discontinuity; indications must be evaluated to decide whether they are relevant, nonrelevant, or false.

An interruption in the normal physical structure or configuration of a part, such as a crack, porosity, or lap; not every discontinuity is a defect.

A discontinuity or combination of discontinuities that exceeds acceptance criteria and renders the part rejectable for its intended service.

An indication caused by an actual discontinuity that requires evaluation against acceptance criteria, as opposed to one caused by geometry or contamination.

An indication arising from a real but acceptable condition such as a surface mark, part geometry, or assembly feature, not from a harmful discontinuity.

An apparent indication produced by something other than the part itself, such as reflections, lighting artifacts, dirt, or optical system defects.

The specified limits, such as maximum allowable indication size or type, that determine whether a part is accepted or rejected after evaluation.

Cleaning and conditioning of the inspection surface, such as removing scale, paint, or oil, so that discontinuities can be seen; inadequate preparation is a common cause of missed indications.

A defined set of inspection parameters, such as viewing angle, distance, lighting, and aids, used to perform a specific visual examination consistently.

A written document describing how a visual examination is to be performed, including equipment, lighting, surface condition, and acceptance criteria; must be qualified and approved.

A document that records the specific parameters of an inspection, such as angles, distances, and lighting, so the technique can be repeated identically.

Comparison of an instrument's readings against a known reference to verify accuracy; light meters, gauges, and imaging systems used in VT are typically subject to periodic calibration.

Demonstration that personnel or equipment meet specified requirements through training, experience, and examination, prior to being certified for the method and level.

Written confirmation that a person has met the qualification requirements of a certification program for a specific method and level.

The highest NDT qualification level; responsibilities include procedure development, technique selection, interpretation of standards, and supervision or examination of lower-level personnel.

A document that adapts an approved procedure to a specific inspection, giving detailed directions for performing the examination and recording results.

A published code or specification, such as an ASTM or ASME document, that defines requirements for the method, acceptance criteria, or personnel qualification.

The documented chain linking a measurement or instrument to a recognized reference standard, supporting confidence in calibration and inspection results.

The surface area immediately surrounding an indication; its reflectance, texture, and color strongly affect whether the indication can be seen.