UT-Ultrasonic Examination: Article 23

linearity (amplitude)

a measure of the proportionality of the amplitude of the signal input to the receiver, and the amplitude of the signal appearing on the display of the ultrasonic instrument or on an auxiliary display.

linearity (time or distance)

a measure of the proportionality of the signals appearing on the time or distance axis of the display and the input signals to the receiver from a calibrated time generator or from multiple echoes from a plate of material of known thickness.

sensitivity

a measure of the smallest ultrasonic signal which will produce a discernible indication on the display of an ultrasonic system.

A-scan

a method of data presentation utilizing a horizontal base line that indicates distance, or time, and a vertical deflection from the base line which indicates amplitude.

focal law

a phased array operational file that defines the search unit elements and their time delays, for both the transmitter and receiver function.

simulation block

a reference block or other item in addition to the basic calibration block that enables correlation of ultrasonic system response initially obtained when using the basic calibration block.

calibration reflector

a reflector with a dimensioned surface which is used to provide an accurately reproducible reference level.

alternative reflector

a reflector, other than the specified reflector, whose

parallel or transverse scan

a scan whereby the probe pair motion is parallel to the ultrasonic beam (e.g., perpendicular to the weld axis).

nonparallel or longitudinal scan

a scan whereby the probe pair motion is perpendicular to the ultrasonic beam (e.g., parallel to the weld axis).

dual search unit

a search unit containing two elements, one a transmitter, the other a receiver.

pulse

a short wave train of mechanical vibrations.

E-scan (also termed an electronic raster scan)

a single focal law multiplexed, across a grouping of active elements, for a constant angle beam stepped along the phased array probe length in defined incremental steps.

linear scanning (also termed line scanning)

a single pass scan of the search unit parallel to the weld axis at a fixed stand-off distance.

loss of back reflection

an absence or significant reduction in the amplitude of the indication from the back surface of the part under examination.

free-run (PA)

recording a set of data without moving the search units.

B-scan (parallel scan)

scan that shows the data collected when scanning the transducer pair in the direction of the sound beam transversely across a weld.

D-scan (nonparallel scan)

scan that shows the data collected when scanning the transducer pair perpendicular to the direction of the sound beam along a weld.

distance-amplitude correction (DAC) curve

see distance-amplitude response curve.

pulse repetition rate

see frequency (pulse repetition).

scanning surface

see test surface.

beam movement

set of focal laws that provides a fan- like series of beams through a defined range of angles using the same set of elements.

back reflection

signal response from the far boundary of the material under examination.

back-wall signal

sound wave that travels between the two transducers with a longitudinal velocity that reflects off the material's back surface.

free run (TOFD)

taking data, without the movement of the probes (e.g., held stationary), of the lateral wave and back-wall reflection to check system software output.

test surface

that surface of a part through which the ultra- sonic energy enters or leaves the part.

indication

that which marks or denotes the presence of a reflector.

shear wave

wave motion in which the particle motion is perpendicular to the direction of propagation.

diffraction

when a wave front direction has been changed by an obstacle or other in-homogeneity in a medium, other than by reflection or refraction.

SAFT-UT

Synthetic Aperture Focusing Technique for ultrasonic testing.

reference block

a block that is used both as a measurement scale and as a means of providing an ultrasonic re- flection of known characteristics.

lateral wave

a compression wave that travels by the most direct route from the transmitting probe to the receiving probe in a TOFD configuration.

reject (suppression)

a control for minimizing or eliminating low amplitude signals (electrical or material noise) so that larger signals are emphasized.

TOFD display

a cross-sectional gray scale view of the weld formed by the stacking of the digitized incremental A-scan data. The two types of scans (parallel and non- parallel) are differentiated from each other by calling one a B-scan and the other a D-scan. Currently there is no standardized terminology for these scans and they may be interchanged by various manufacturers (e.g., one calling the scan parallel to the weld axis a B-scan and another a D-scan).

distance-amplitude response curve

a curve showing the relationship between the different distances and the amplitudes of ultrasonic response from targets of equal size in an ultrasonic response from targets of equal size in an ultrasonic transmitting medium.

attenuator

a device for altering the amplitude of an ultra- sonic indication in known increments, usually decibels.

beam spread

a divergence of the ultrasonic beam as the sound travels through a medium.

scan plan

a documented examination strategy that pro- vides a standardized and repeatable methodology for weld examinations. The scan plan displays cross-sectional joint geometry, extent of coverage, clad or overlay (if present), heat affected zone (HAZ) extent, search unit size(s) and frequency(ies), beam plots of all angles used, search unit(s) position in relation to the weld centerline [probe center spacing (PCS) in the case of time of flight diffraction (TOFD)], search unit mechanical fixturing de- vice, and if applicable, zonal coverage overlap.

attenuation

a factor that describes the decrease in ultra- sound intensity with distance; normally expressed in decibel per unit length.

single (fixed angle)

a focal law applied to a specific set of active elements for a constant angle beam, emulating a conventional single element probe.

B-scan presentation

a means of ultrasonic data presentation which displays a cross section of the specimen indicating the approximate length (as detected per scan) of reflectors and their relative positions.

back-wall echo

a specular reflection from the back-wall of the component being examined.

fracture mechanics based

a standard for acceptance of a weld based on the categorization of imperfections by type (i.e., surface or subsurface) and their size (i.e., length and through-wall height).

couplant

a substance used between the search unit and examination surface to permit or improve transmission of ultrasonic energy.

examination system

a system that includes the ultrasonic instrument, search unit cable, and search unit.

contact testing

a technique in which the search unit makes contact directly with the test piece through a thin layer of couplant.

semi-automated ultrasonic examinations (SAUT)

a technique of ultrasonic examination performed with equipment and search units that are mechanically mounted and guided, manually assisted (driven), and which may be manually adjusted by the technician. The equipment used to perform the examinations is capable of recording the ultrasonic response data, including the scanning positions, by means of integral encoding devices such that imaging of the acquired data can be performed.

automated ultrasonic examinations (AUT)

a technique of ultrasonic examination performed with equipment and search units that are mechanically mounted and guided, remotely operated, and motor-controlled (driven) with- out adjustments by the technician. The equipment used to perform the examinations is capable of recording the ultrasonic response data, including the scanning positions, by means of integral encoding devices such that imaging of the acquired data can be performed.

Manual Ultrasonic Examinations (MUT) or Encoded Manual Ultrasonic Examinations (EMUT)

a technique of ultrasonic examination performed with search units that are manipulated by hand without the aid of any mechanical guidance system. Manual techniques may be encoded such that imaging of the acquired data can be performed.

angle beam

a term used to describe an angle of incidence or refraction other than normal to the surface of the test object, as in angle beam examination, angle beam search unit, angle beam longitudinal waves, and angle beam shear waves.

through transmission technique

a test procedure in which the ultrasonic vibrations are emitted by one search unit and received by another at the opposite surface of the material examined.

straight beam

a vibrating pulse wave train traveling nor- mal to the test surface.

search unit

an electro-acoustic device used to transmit or receive ultrasonic energy or both. The device generally consists of a nameplate, connector, case, backing, piezoelectric element, wearface, or lens, or wedge.

transducer

an electro-acoustical device for converting electrical energy into acoustical energy and vice versa. See also crystal in Article 30, SE-1316, Section I.

electric simulator

an electronic device that enables correlation of ultrasonic system response initially obtained employing the basic calibration block.

pulse-echo method

an inspection method in which the presence and position of a reflector are indicated by the echo amplitude and time.

holography (acoustic)

an inspection system using the phase interface between the ultrasonic wave from an object and a reference signal to obtain an image of reflectors in the material under test.

reflector

an interface at which an ultrasonic beam en- counters a change in acoustic impedance and at which at least part of the energy is reflected.

C-scan

an ultrasonic data presentation which provides a plan view of the test object, and discontinuities therein.

D-scan

an ultrasonic data presentation which provides an end view of the specimen indicating the approximate width (as detected per scan) of reflectors and their relative positions.

immersion testing

an ultrasonic examination method in which the search unit and the test part are submerged (at least locally) in a fluid, usually water.

noise

any undesired signal (electrical or acoustic) that tends to interfere with the reception, interpretation, or processing of the desired signal.

static calibration

calibration for examination wherein the search unit is positioned on a calibration block so that the pertinent reflectors can be identified and the instrumentation adjusted accordingly.

dynamic calibration

calibration that is conducted with the search unit in motion, usually at the same speed and direction of the actual test examination.

CRT

cathode ray tube.

computerized imaging

computer processed display or analysis and display of ultrasonic data to provide two or three dimensional surfaces.

calibration

correlation of the ultrasonic system response(s) with calibration reflector(s).

split DAC curves

creating two or more overlapping screen DAC curves with different sensitivity reference level gain settings.

piezoelectric element

crystal or polycrystal materials which when mechanically deformed, produce electrical charges, and conversely, when intermittently charged, will deform and produce mechanical vibrations.

diffracted signals

diffracted waves from the upper and lower tips of flaws resulting from its interaction with the incident sound wave.

axial direction

direction of sound beam parallel to component's major axis.

circumferential direction

direction of sound beam perpendicular to (cylindrical) component's major axis.

frequency (inspection)

effective ultrasonic wave frequency of the system used to inspect the material.

multiple back reflections

in ultrasonic straight beam examination, successive reflections from the back and front surfaces of the material.

echo

indication of reflected energy. effective height: the distance measured from the outside

damping, search unit

limiting the duration of a signal from a search unit subject to a pulsed input by electrically or mechanically decreasing the amplitude of successive cycles.

S-scan (also called a Sector, Sectorial, or Azimuthal scan)

may refer to either the beam movement or the data display.

resolution

the ability of ultrasonic equipment to give simultaneous, separate indications from discontinuities having nearly the same range and lateral position with respect to the beam axis.

refraction

the angular change in direction of the ultrasonic beam as it passes obliquely from one medium to an- other, in which the waves have a different velocity.

interface

the boundary between two materials.

search unit mechanical fixturing device

the component of an automated or semi-automated scanning apparatus attached to the scanner frame that secures the search unit or search unit array at the spacing and offset distance specified by the scan plan and that provides for consistent contact (for contact techniques) or suitable water path (for immersion techniques).

probe center spacing (PCS)

the distance between the marked exit points of a pair of TOFD probes for a specific application.

acoustic pulse

the duration of time between the start and end of the signal when the amplitude reaches 10% of the maximum amplitude.

range

the maximum sound path length that is displayed.

scanning

the movement of a search unit relative to the test piece in order to examine a volume of the material.

frequency (pulse repetition)

the number of times per second an electro-acoustic search unit is excited by the pulse generator to produce a pulse of ultrasonic energy. This is also called pulse repetition rate.

signal-to-noise ratio

the ratio of the amplitude of an ultra- sonic indication to the amplitude of the maximum back- ground noise.

initial pulse

the response of the ultrasonic system display to the transmitter pulse (sometimes called main bang).

time-of-flight

the time it takes for a sound wave to travel from the transmitting transducer to the flaw, and then to the receiving transducer.

base line

the time of flight or distance trace (horizontal) across the A-scan CRT display (for no signal condition).

ringing time

the time that the mechanical vibrations of a piezoelectric element continue after the electrical pulse has stopped.

mode

the type of ultrasonic wave propagating in the materials as characterized by the particle motion (for example, longitudinal, transverse, and so forth).

primary reference response (level)

the ultrasonic response from the basic calibration reflector at the specified sound path distance, electronically adjusted to a specified percentage of the full screen height.

sweep

the uniform and repeated movement of an electron beam across the CRT.

amplitude

the vertical pulse height of a signal, usually base to peak, when indicated by an A-scan presentation.

longitudinal wave

those waves in which the particle motion of the material is essentially in the same direction as the wave propagation.

decibel (dB)

twenty times the base ten logarithm of the ratio of two ultrasonic signal amplitudes, dB = 20 log 10 (amplitude ratio).

data display

two-dimensional view of all A-scans from a specific set of elements corrected for delay and refracted angle. Volume-corrected S-scan images typically show a pie-shaped display with defects located at their geometrically correct and measurable positions.

examination coverage

two-directional search unit beam coverage, both parallel and perpendicular to the weld axis, of the volume specified by the referencing Code Section. Perpendicularly oriented search unit beams are directed from both sides of the weld, when possible, with the angle(s) selected to be appropriate for the configuration being examined.