ASNT NDT III ET flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Eddy current generation principle

A time-varying current in a coil produces a changing magnetic field that induces circulating currents in a nearby conductor, following Faraday's law of electromagnetic induction.

Impedance plane display

A two-dimensional plot of coil impedance components, where changes in conductivity, permeability, lift-off, and discontinuities appear as characteristic vector directions and phase angles.

Standard depth of penetration

The depth at which eddy current density falls to 36.8 percent of its surface value, calculated as delta equals one over the square root of pi times frequency times permeability times conductivity.

Effective penetration depth

Approximately three standard depths of penetration, the practical limit beyond which eddy current signals from discontinuities are too attenuated to detect reliably.

Fill factor

The ratio of the test object's cross-sectional area to the coil's cross-sectional area; a higher fill factor improves coupling and increases signal amplitude.

Lift-off effect

The change in coil impedance caused by the gap between coil and test surface; it produces a phase shift that can mask discontinuities unless compensated or phase-separated.

Absolute coil

A single sensing coil that measures the total impedance of the test region, sensitive to gradual property changes but susceptible to drift and lift-off variation.

Differential coil

Two opposing sensing coils connected to reject common-mode effects such as temperature and lift-off, but insensitive to gradual changes occurring over both coils.

Phase analysis

A technique using the phase angle of the impedance-plane signal to distinguish discontinuity depth, conductivity, permeability, and geometric effects from one another.

Test frequency selection

Frequency is chosen so penetration reaches the required depth while resolution remains adequate; higher frequency gives shallower penetration and greater sensitivity to surface flaws.

Conductivity measurement

Eddy current conductivity testing compares coil response against known standards; it is used for alloy sorting and heat-treatment verification in nonmagnetic metals.

Permeability effect

Ferromagnetic materials concentrate magnetic flux, drastically reducing penetration and adding noise; permeability must be reduced or saturated for effective eddy current testing.

Reference standard block

A block of known material and dimensions containing artificial discontinuities, used to establish gain, phase, and acceptance thresholds for the inspection.

Magnetic flux leakage

A method in which magnetization of a ferromagnetic part causes flux to leak at surface or near-surface discontinuities, detected by sensors such as Hall probes or coils.

Signal-to-noise ratio

The ratio of discontinuity signal amplitude to background noise; higher ratios improve detection reliability and are improved by filtering, shielding, and better coupling.

Remote field testing

An eddy current technique using through-transmission of a low-frequency field along a pipe wall, allowing inspection of ferromagnetic tubing from the inside.

Written practice

The employer-issued document that defines qualification, examination, and certification requirements for NDT personnel, consistent with SNT-TC-1A or another recognized standard.

Level III responsibilities

The Level III establishes techniques, approves procedures, interprets codes and standards, and certifies or designates personnel for the method in which certified.

Discontinuity versus defect

A discontinuity is any interruption in material continuity; a defect is a discontinuity that exceeds acceptance criteria or impairs the part's serviceability.

Probability of detection

The statistical likelihood that an inspection finds a discontinuity of given size, orientation, and location; it increases with size and favorable orientation but never reaches 100 percent.

Near vision acuity requirement

Annual verification of near vision at 12 inches (30 cm), typically Jaeger J1 or equivalent, plus color perception testing as specified in the written practice.

Certification examination structure

Level II certification typically requires passing general, method-specific, and practical examinations, plus documented experience and satisfactory vision tests.

Recertification interval

The period after which certification must be renewed, defined by the employer's written practice; typical intervals are three to five years with periodic performance checks.

Traceability of standards

Reference standards must be documented, uniquely identified, and traceable to recognized sources, and their response verified before and after inspection.

Technique versus procedure

A technique is a specific detailed way of applying a method; a procedure is the documented, approved set of instructions governing the inspection.

Method versus technique

A method is a broad NDT discipline such as eddy current testing; a technique is a specific application of that method with defined parameters and equipment.

Acceptance criteria

The limits specified by code, standard, or contract that define whether an indicated discontinuity is acceptable or must be rejected and repaired.

Calibration versus verification

Calibration establishes instrument response against a traceable reference; verification confirms that response remains within specified limits at defined intervals.

False indication

A signal that appears on the instrument but is not caused by a discontinuity, such as lift-off, geometry, or electrical interference, and must be resolved by the examiner.

Inspection report content

Documentation of method, technique, equipment, standards, parameters, results, acceptance criteria, examiner identity and certification level, and date of inspection.

Skin effect

The tendency of alternating current to concentrate near the conductor surface, causing current density to decrease exponentially with depth and limiting eddy current penetration.