ASNT NDT Level III flashcards

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

Acoustic impedance

Z = rho*v, the product of density and sound velocity. Differences in acoustic impedance between two media determine how much ultrasonic energy is reflected at their interface.

Shear wave velocity in steel

About 3230 m/s, roughly half the 5900 m/s longitudinal velocity. Shear waves cannot propagate in liquids or gases because those media have no shear stiffness.

Austenitic stainless and magnetic particle

Austenitic stainless steel is essentially nonmagnetic at room temperature, so magnetic particle inspection cannot be used; penetrant or eddy current testing is chosen instead.

Carbon equivalent

IIW formula CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Values above about 0.40 indicate increased hardenability and cold-cracking risk in welded carbon steel.

Attenuation versus grain size

Ultrasonic attenuation increases with grain size and frequency because coarse grains scatter the beam. Coarse cast structures and austenitic weld metal therefore require lower test frequencies.

Precipitation hardening treatment

Solution treatment dissolves alloying elements, quenching retains a supersaturated solid solution, and aging precipitates fine particles that raise strength and hardness.

Hydrogen-induced cold cracking

A delayed weld crack requiring diffusible hydrogen, a hard susceptible microstructure and tensile restraint. It can appear hours after welding, so inspection is often delayed.

Lack of fusion

A planar weld discontinuity where deposited metal fails to bond to the base metal or to a previous pass; it lies roughly parallel to the weld axis.

Solidification hot cracking

Cracks forming at the end of weld solidification along grain boundaries weakened by low-melting films, promoted by high restraint, high sulfur or deep narrow beads.

Rolling lamination

A flattened planar discontinuity parallel to the plate surface, formed from inclusions or pipe during rolling; it is best detected by straight-beam scanning normal to that surface.

Casting shrinkage cavity

An irregular internal void formed where the last metal solidified without feed metal; it is usually located at thermal centers and is larger toward the riser side.

Heat-affected zone

Base metal adjacent to a weld that is thermally altered but not melted; it may show grain coarsening and a hardness peak that raises cracking risk.

Near field length

N = D^2/(4*lambda). Within this distance from a flat transducer the beam is complex and amplitude does not fall off monotonically, so defects are best evaluated beyond it.

Snell's law for refraction

sin(theta1)/v1 = sin(theta2)/v2 relates incidence and refraction angles at an interface; it governs the incidence angle needed to produce a desired refracted shear wave.

Radiographic geometric unsharpness

Ug = F*t/d, where F is source size, t the source-side object-to-film distance and d the source-to-object distance. A smaller source and larger d sharpen the image.

Post-emulsifiable penetrant

A penetrant method in which excess penetrant is removed by a separate emulsifier applied after the dwell period, giving good sensitivity and control on rough or complex surfaces.

Eddy current penetration depth

Penetration decreases as frequency, electrical conductivity or magnetic permeability increases. Lower frequency and lower conductivity allow deeper penetration into the test part.

AC yoke lifting power

An AC electromagnetic yoke must lift at least 10 lb (4.5 kg) at maximum pole spacing, while a DC yoke must lift about 40 lb (18 kg).

Shall, should and may

In codes, shall denotes a mandatory requirement, should a recommendation and may a permissive option; this convention determines whether a clause is enforceable.

ASME Section IX scope

It qualifies welding and brazing procedures and the performance of welders, brazers and operators; product acceptance criteria reside in the construction section instead.

Code versus specification

A code is a mandatory body of rules adopted by law or contract, while a specification states a purchaser's detailed requirements for a product, material or service.

Procedure qualification record

A PQR documents the actual welding variables and test results used to qualify a welding procedure specification; it is a factual record rather than a working procedure.

ASME Section V Article 6

It contains mandatory requirements for liquid penetrant examination, covering materials, surface preparation, dwell times, excess removal, development and interpretation of indications.

UT versus RT for planar defects

Ultrasonic testing detects planar discontinuities such as cracks and lack of fusion when the beam is normal to them; radiography is weaker because such defects may not change thickness.

Method selection inputs

Discontinuity type and orientation, material, geometry and access, surface condition, governing code requirements, inspection speed and cost all determine which NDT method is chosen.

Probability of detection

POD describes the fraction of defects of a given size found by a technique; it depends on method, procedure, defect orientation, operator and equipment.

Acceptance criteria source

Limits derive from service loads, fracture mechanics, safety factors and the governing code, and are fixed before inspection rather than adjusted to the results.

Reference standard for qualification

A block or sample containing known artificial or natural defects, used to demonstrate that a technique achieves the required sensitivity, coverage and sizing accuracy.

SNT-TC-1A

An ASNT recommended practice under which the employer writes an NDT written practice defining training, experience, examination and certification requirements for Levels I, II and III.

Qualification versus certification

Qualification is the demonstrated ability to perform a task; certification is the written attestation by the employer or certifying body that qualification requirements have been met.

Level III responsibilities

Selecting methods, interpreting codes, writing and approving procedures, establishing acceptance criteria, training and certifying personnel, and interpreting inspection results.

Near vision requirement

Certified personnel must read Jaeger 1 or equivalent type at 12 in (30 cm) with at least one eye, annually, and demonstrate color contrast differentiation.