This glossary collects the main technical terms used on ultrasuonindt.it and in the practice of ultrasonic non-destructive testing (NDT): physical principles of measurement, scanning modes, transducer types, calibration, reference standards, data management software and Dakota NDT commercial terminology. It is intended as a quick reference for inspectors, NDT technicians, maintenance engineers and designers who want a single, verified point of reference. For each entry, where applicable, links are given to the product pages, technical articles and guides published on the site.
The definitions adopt the terminology found in the Dakota NDT manuals, in the EN, ASTM, API, AWS and ASME standards cited on the site and in the technical literature of the sector. The Dakota trade names (ThruPaint™, DakMaster™, DakView™, MiniMax, Max II) are quoted alongside the corresponding technical terms to make it easier to match the manufacturer’s documentation with standard nomenclature.
Alphabetical index
Select the letter or the term to jump directly to the corresponding definition. Each entry in turn contains a link to return to this index.
A · Ultrasonic couplant · Accuracy · AGC – Automatic Gain Control · API 570 · API 653 · A-Scan · ASME PCC-1 · Asset Integrity Management · ASTM E797 · Ultrasonic attenuation · AWS D1.1
B · Benchtop · Calibration block · Bolt Tension Monitor · B-Scan
C · Calibration (1-point and 2-point) · Ultrasonic coaxial cable · CT – Coating Thickness · CML – Condition Monitoring Location · Composites · Temperature compensation · Connectors (LEMO, BNC, Microdot, ODU) · Non-Destructive Testing (NDT) · Corrosion · Wedge
D · DAC – Distance Amplitude Correction · DakMaster™ · DakView™ · Datalogger · Delay line tip · DGS – Distance Gain Size · Defect / discontinuity · Dual element
E · Echo-Echo (EE) / ThruPaint™ · Echo-Echo Verify (EEV) · Ultrasonic elongation · EN 12668-1 · EN 14127 · EN 15317 · EN 4179
F · Fastener · Flaw detector · Forging · Probe frequency
G · Gain · Grid batching and grid file
H · High Penetration · High Temperature transducer
I · Indication rating (AWS) · IP65 · Pulse-Echo (PE) · Coded inspection
M · Grid mapping · MIL-STD-45662A · Multi-Echo
N · NADCAP · NIST · Nodularity (test)
P · Dakota Part Number · PECT – Pulse-Echo Coating Through · PETP – Pulse-Echo Through Paint · Pencil probe · Pitting · Plastic Mode (Interface-Echo) · PRF – Pulse Repetition Frequency
R · Measuring range · Corrosion rate and remaining life · Resolution · Coating
S · Weld · Scan Mode · Sequential file · User setup · Shear wave · Single element · Ultrasonic probe (transducer) · Sonic Tester · Ultrasonic thickness gauge · Step block
T · TCG – Time Corrected Gain · Traceability (NIST / MIL-STD) · TRIG · Piping
U · Ultrasound · Underwater transducer · USB-C
V · Sound velocity · Velocity Mode
Need help choosing the right product?
A
Ultrasonic couplant
Viscous liquid or gel placed between the active face of the transducer and the surface of the test material, whose function is to eliminate the air layer that would prevent transmission of the ultrasonic wave through total reflection at the interface. The choice of couplant directly affects the quality of the A-Scan and the accuracy of the measurement: high-viscosity couplants suit vertical surfaces and room temperature, while high-temperature applications require specific formulations stable up to about 398 °C. On contact with sensitive materials (austenitic stainless steels, nickel alloys, food or nuclear applications) the use of certified couplants with low sulphur, halogen and chloride content is mandatory. All Dakota couplants distributed by RODER SRL cover the range from -15 °C to about 398 °C and are compatible with horizontal and vertical application.
Further reading: Ultrasonic couplant liquids, How to improve results on difficult materials.
Accuratezza
Indicates the maximum permitted difference between the value measured by the instrument and the true value of the quantity, once calibration has been correctly performed. In Dakota thickness gauges accuracy is specified as an absolute error (for example ±0.01 mm on ZX models, ±0.05 mm on the CX series, down to ±0.001 mm on the Precision PMX and PCX models) and is valid under the declared conditions of temperature, reference probe and calibrated material. Accuracy should not be confused with resolution, which is the smallest variation displayable on the screen, nor with repeatability, which describes the scatter between successive readings on the same point. For applications requiring micron-level accuracy, such as the inspection of aeronautical sheet in aluminium or titanium alloy, it is essential to validate the instrument with a certified block and to operate under stable thermal conditions.
Further reading: 1-point vs 2-point calibration, NDT in aerospace.
AGC – Automatic Gain Control
Function that automatically adjusts the receiver gain so as to keep the amplitude of the return echo constant within the measuring window, regardless of variations in coupling or material attenuation. AGC is particularly useful in scan-mode inspections on irregular or corroded surfaces, where the signal level can vary significantly from one point to the next: the instrument compensates in real time, reducing lost readings and trigger errors on the surface echo. All professional-grade Dakota thickness gauges (CMX, MX, PMX, PCX series) and the FX flaw detectors integrate AGC; combined with TCG, it allows flaw detectors to analyse deep echoes in attenuating materials. Activating AGC does not replace calibration, but completes its effectiveness in the field.
Further reading: Dakota FX70-DL, Dakota CMX10-DL.
API 570
API (American Petroleum Institute) standard for the inspection, repair, alteration and rerating of in-service piping in oil & gas and petrochemical plants. It defines inspection frequencies, personnel qualification, documentation requirements and acceptance criteria based on CMLs (Condition Monitoring Locations) managed with a structured data archive and calculation of the corrosion rate and remaining life. The standard requires instruments with an internal datalogger, a ThruPaint mode to measure through coatings without removing them and the ability to export data in a format compatible with asset integrity management systems. Dakota thickness gauges of the CMX and MX families fully meet these requirements, combined with the DakMaster™ software for reporting.
Further reading: API 570 and API 653: instrumentation requirements, Pipeline corrosion inspection to API 570.
API 653
API standard for the inspection, repair, alteration and reconstruction of welded atmospheric storage tanks. It governs the mapping of shells and bottoms through ultrasonic thickness measurements distributed on a grid, the management of CMLs, the assessment of the minimum allowable thickness and the calculation of the next inspection interval. To comply with the standard, instrumentation is needed with an extended datalogger, fast scan mode (200–250 readings/second), data storage in grid or sequential format and calibration traceability (NIST, MIL-STD-45662A). The Dakota MX1-DL, MX2-DL, CMX and CMX10-DL gauges cover these requirements and interface via USB-C with DakMaster™ for automatic report generation.
Further reading: Storage tank thickness inspection to API 653, API 570 / 653 requirements.
A-Scan
Graphic representation of the received ultrasonic signal as a function of time, with the signal amplitude on the vertical axis (generally expressed as a percentage of screen height or in dB) and the time of flight on the horizontal axis, convertible into distance once the sound velocity in the material is known. The A-Scan is the fundamental diagnostic tool of ultrasonic inspection: it makes it possible to distinguish interface echoes, back-wall echoes and any flaw echoes, to assess the signal-to-noise ratio and to validate the quality of coupling before accepting the measurement. In Dakota thickness gauges it is available on the professional models (CMX, MX, PMX, PCX) and is considered indispensable in every coded inspection and every measurement on critical material, while the entry-level models (CX2, CX4, ZX) return the numerical value only. On flaw detectors the A-Scan is the primary display.
Further reading: How ultrasonic measurement works, DakView™ for A-Scan analysis on the PC, MX1-DL vs MX2-DL comparison.
ASME PCC-1
ASME (American Society of Mechanical Engineers) Post Construction Committee guideline dedicated to assembly practices for gasketed flanged joints in pressure boundaries. It defines procedures for selecting gasket and bolting, lubrication, cleaning of the faces, tightening sequence and control of the final tension, including ultrasonic measurement methods for bolt elongation as an alternative or complement to tightening torque. Reference to ASME PCC-1 is now required in many project specifications in the oil & gas, energy and chemical sectors for critical pressure applications. The Dakota BT1-DL and BT2-DL instruments are designed to provide the ultrasonic elongation measurement required by the appendices of the standard with accuracy in the order of 0.0001 mm.
Further reading: ASME PCC-1: the reference standard, Tightening of pressure flanges.
Asset Integrity Management
Discipline that integrates inspections, maintenance and data analysis to ensure that industrial plants (piping, tanks, pressure vessels, offshore structures) operate within their design safety limits for their entire service life. It is based on the systematic, traceable collection of ultrasonic thickness measurements at predefined CMLs, with calculation of the corrosion rate, assessment of the minimum allowable thickness (Tmin) and planning of the next inspection interval. It requires instrumentation with an extended datalogger, structured storage capability in batches or grids and reporting software such as DakMaster™. The Dakota MX and CMX family is the Dakota reference for asset integrity in the API 570 and API 653 field.
Further reading: Monitoring uniform corrosion, Dakota MX2-DL.
ASTM E797
American ASTM standard “Standard Practice for Measuring Thickness by Manual Ultrasonic Pulse-Echo Contact Method”: it is the international reference for the manual ultrasonic thickness measurement procedure with the pulse-echo contact method. It defines requirements for calibration, probe selection, surface conditions, coupling, test frequency and reporting. All Dakota thickness gauges distributed by RODER SRL are declared compliant with ASTM E797 and calibrated with NIST and MIL-STD-45662A traceability. European equivalent: EN 14127; for instrument qualification EN 15317 applies.
Further reading: NDT standards for thickness measurement.
Ultrasonic attenuation
Decrease in the amplitude of the ultrasonic wave with the distance travelled in the material, due to the combination of absorption, beam divergence and scattering on the microstructure. It is expressed in dB/mm and depends strongly on probe frequency, grain size, presence of second phases or porosity: cast irons, coarse-grained alloys, composites and plastics show attenuation values that require low-frequency probes, high transmission energy and advanced gain functions (AGC, TCG). The Dakota PMX4-DL High Penetration gauges and the FX70-DL/FX81-DL flaw detectors are specifically sized to overcome the attenuation problems typical of difficult materials.
Further reading: Measurements on difficult materials, Dakota PMX4-DL.
AWS D1.1
Code of the American Welding Society “Structural Welding Code – Steel”: it governs the design and qualification of structural steel welds, processes and welders. Clause 6 and Annex K detail the requirements for ultrasonic weld inspection, prescribing calibration blocks, angle (shear wave) probes at 45°, 60° and 70°, calculation of the indication rating and acceptance criteria. The Dakota FX70-DL, FX71-DL and FX81-DL flaw detectors integrate a dedicated AWS toolkit that automates the determination of the indication rating value from the calibration parameters, reducing the risk of error in the field.
Further reading: AWS D1.1 and ultrasonic weld inspection, AWS D1.1 inspection with the Dakota FX70-DL.
B
Benchtop
NDT instrument configuration designed for bench use in the laboratory or workshop, with larger dimensions than its portable counterpart, mains power supply and a larger display. The benchtop form factor favours reading ergonomics, storage capacity, multi-channel operation and stationary applications such as production quality control, probe calibration and forensic inspections on dismantled components. In the Dakota range the benchtop versions include the FX81-DL flaw detector and the BT2-DL Max II bolt tension monitor. The benchtop version of the FX81-DL shares the same electronics as the portable FX70-DL, but offers greater operating comfort for non-field use.
Further reading: Portable or benchtop: FX70 vs FX81, BT1 vs BT2.
Calibration block
Reference artefact, generally in 4340 steel (or in the material to be calibrated), with one or more known thicknesses certified within tight tolerances (typically ±1%), used to calibrate the thickness gauge or flaw detector before measuring. Blocks may be single (one thickness) or multi-step blocks, suitable for 2-point calibration over a wide range. Each block is accompanied by a NIST and MIL-STD-45662A traceable calibration certificate. Inspection planning must provide for blocks consistent with the test material, the probe used and the expected measuring range.
Further reading: Calibration blocks, Step block, 1-point vs 2-point calibration.
Bolt Tension Monitor
Ultrasonic instrument dedicated to measuring the tension applied to a bolt by detecting the elongation of the fastener. Unlike the torque wrench, which produces scatter of ±25-30% on the actual tension because of friction, ultrasonic measurement directly provides the applied load with accuracy in the order of 0.0001 mm, independent of friction, lubrication and bolt diameter. It requires automatic temperature compensation and an initial calibration of the acoustic factor of the bolt material. The Dakota range includes the portable BT1-DL MiniMax model and the benchtop BT2-DL Max II, the latter capable of handling tie rods up to 30 metres long for offshore and wind turbine applications.
Further reading: Bolt tension monitors, Tightening of pressure flanges, Bolt tension on wind turbines.
B-Scan
Two-dimensional representation of thickness along the transducer’s scanning path: the horizontal axis corresponds to position (or scanning time), the vertical axis to the echo distance (and therefore to thickness). It makes it possible to immediately visualise the profile of a metallographic section hidden by the coating, to identify areas of localised pitting, to assess the thinning gradient and to store the waveform of the entire scan for subsequent analysis. The B-Scan is available on the Dakota CX8-DL, MX1-DL, MX2-DL, PCX8-DL and CMX10-DL models, as well as on the FX70-DL, FX71-DL and FX81-DL flaw detectors. The DakView™ software allows playback and documentation of the recorded B-Scans.
Further reading: Dakota MX2-DL, DakView™.
C
Calibration (1-point and 2-point)
Periodic calibration procedure for the thickness gauge or flaw detector performed on one or more reference blocks of known thickness, aimed at correcting the offset and gain of the measuring chain before use in the field. 1-point calibration corrects only the zero-time offset and is quick, suitable for narrow ranges and for new probes with standard materials. 2-point calibration acts on two thicknesses (a minimum and a maximum of the application range) and corrects both offset and gain: it is the recommended procedure for measurements over wide ranges, special materials, worn probes or under non-standard thermal conditions. All Dakota thickness gauges support both modes; documentation of the calibration process is an integral part of the inspection report.
Further reading: 1-point vs 2-point calibration, RODER SRL support and periodic calibration.
Ultrasonic coaxial cable
Shielded cable connecting the transducer to the instrument, sized to minimise electromagnetic noise and high-frequency signal loss. The choice of cable (length, impedance, shielding) affects the quality of the A-Scan and the maximum usefully inspectable depth, especially with low-frequency probes for attenuating materials. The Dakota range provides cables with various standard connectors (LEMO 00, BNC, Microdot, ODU Smart Port) to cover all catalogue instruments, with typical lengths from 1.2 m to 3 m and dual element versions for corrosion gauges.
Further reading: Transducer cables, Connectors.
CT – Coating Thickness
Ultrasonic measuring mode in which the instrument returns only the thickness of the coating (paint, epoxy, rubber) applied to the metal substrate, ignoring the thickness of the underlying metal. Operationally it is the complement of the Echo-Echo (ThruPaint™) mode, which instead returns the metal only: the combination of the two gives the complete picture of the inspection of coated piping and tanks. CT mode is available on the top-of-the-range Dakota CMX10-DL gauges among the 6 measuring modes (PE, PECT, PETP, EE, EEV, CT).
Further reading: Dakota CMX10-DL, Echo-Echo and ThruPaint™.
CML – Condition Monitoring Location
Fixed thickness-monitoring point uniquely identified on an asset (piping, tank, pressure vessel), where ultrasonic measurements are repeated periodically to build a historical trend. CMLs are the foundation of API 570 and API 653 inspections: their distribution, number and survey frequency are planned according to risk, expected corrosion rate and process criticality. Instruments such as the Dakota CMX, MX1-DL and MX2-DL make it possible to store the measurements in a grid or sequential structure associated with each CML, with export to DakMaster™ for automatic trend analysis.
Further reading: Monitoring uniform corrosion, Pipeline corrosion inspection.
Composites
Multiphase materials consisting of a matrix (polymer, ceramic, metal) and a reinforcing phase (carbon, glass, aramid fibres). They are characterised by high ultrasonic attenuation and structural inhomogeneity that make standard measurement difficult: reliable inspection requires low-frequency probes, high transmission energy and advanced gain functions (AGC, TCG). The Dakota PMX4-DL High Penetration is sized for fibre composites, thick plastics and castings; the FX flaw detectors allow the detection of delaminations and disbonds.
Further reading: Dakota PMX4-DL, Measurements on difficult materials.
Temperature compensation
Function that automatically corrects the drift of the sound velocity in the material as temperature varies, keeping measurement accuracy constant. It is particularly critical in bolt tension monitoring applications, where a variation of a few degrees can alter the elongation reading by amounts comparable to the applied load. The Dakota BT1-DL and BT2-DL monitors integrate a temperature sensor on the bolt head (or a manual compensation parameter) that feeds the calculation algorithm in real time, allowing controlled tightening independent of ambient conditions. On precision thickness gauges temperature compensation is available as a velocity-temperature setup.
Further reading: Dakota BT1-DL, BT1 vs BT2.
Connectors (LEMO, BNC, Microdot, ODU)
Electromechanical coupling standard between cable and instrument. On Dakota products the main connectors are LEMO 00 (bayonet, self-centring, robust and resistant to harsh environments), BNC (historic, widely used on laboratory instruments), Microdot (compact, typical of high-density dual element probes) and ODU Smart Port (multi-way on the CMX10-DL, handles dual, single, delay and pencil probes). The choice of connector is dictated by the instrument model: the transducer cables page gives the complete compatibility matrix.
Further reading: Dakota transducer cables.
Non-Destructive Testing (NDT)
Set of test techniques that make it possible to assess the properties, integrity and dimensions of a component or a weld without altering its service characteristics. The main methods include: visual (VT), liquid penetrant (PT), magnetic particle (MT), eddy current (ET), radiography (RT) and ultrasonic (UT). Ultrasonic thickness measurement and UT flaw detection, the subject of the Dakota catalogue distributed by RODER SRL, are the most widespread volumetric NDT technique for the inspection of metal, plastic and composite components in the oil & gas, energy, marine, aerospace and manufacturing sectors. Personnel qualifications are governed by standards such as UNI EN ISO 9712, NAS 410 and EN 4179.
Further reading: How ultrasonic measurement works, Industrial applications, About us.
Corrosion (uniform, localised, under coating)
Electrochemical degradation of the material leading to loss of wall thickness. It occurs in uniform form (loss distributed over a wide area at a constant rate), localised form as pitting (corrosion concentrated in small, deep craters) or under coating (CUI – Corrosion Under Insulation, typical of insulated and painted piping, where the presence of moisture under the coating accelerates degradation). Uniform corrosion is monitored with periodic measurements at CMLs; localised forms require A-Scan and B-Scan mapping to be characterised; CUI typically requires ThruPaint™ (Echo-Echo) or PECT mode to measure through the coating without removing it.
Further reading: Monitoring uniform corrosion, PECT mode, Echo-Echo and ThruPaint™.
Wedge (transducer wedge)
Hard plastic element (typically Rexolite or Plexiglas) mounted between the single element transducer and the surface of the material, which converts the longitudinal wave generated by the crystal into a transverse (shear) wave inclined at a predefined angle (45°, 60° or 70° in steel). Wedges are the heart of weld inspection to AWS D1.1 and EN ISO 17640: the angled geometry makes it possible to intercept planar defects such as lack of fusion, lack of penetration and fatigue cracks. The Dakota range offers transducer wedges in both standard and quick-change versions, paired with shear wave probes.
Further reading: Transducers for flaw detectors, Shear wave.
D
DAC – Distance Amplitude Correction
Reference curve, built by acquiring the echo of a reflector of known geometry (typically a flat-bottom hole or a side-drilled hole) at increasing depths, which describes the attenuation of the signal as the distance travelled in the material varies. The DAC makes it possible to compare the amplitude of a real indication with the value expected at that same depth, classifying the flaw according to the criteria of the reference standard. It is a standard function on the Dakota FX70-DL/FX71-DL and FX81-DL flaw detectors and is configured with a variable number of points (typically up to 16 on the CMX10-DL and up to 50 on the flaw detectors). It is often combined with TCG and DGS to cover the whole regulatory framework.
Further reading: Dakota FX70-DL, AWS D1.1 and UT inspection.
DakMaster™
Official Dakota NDT software for managing and archiving measurements from thickness gauges, flaw detectors and bolt tension monitors with integrated datalogger. It allows data download via USB or Bluetooth, the creation and management of calibration setups, the generation of professional reports in standard format, trend analysis on CMLs and export to Excel and CSV. It is available for Windows and MacOS X. DakMaster™ is the operational reference for API 570 and API 653 coded inspections and for production quality control.
Further reading: DakMaster™: managing and archiving NDT measurements, Data logger vs manual recording.
DakView™
Dakota NDT software for PC analysis of the A-Scan and B-Scan waveforms acquired by ultrasonic instruments. It allows the measuring gates to be repositioned, the gain to be re-evaluated, the ultrasonic signal to be visually documented and images to be extracted for insertion in inspection reports. Available for Windows 32/64 bit and Mac OS X, it is particularly useful in coded inspections where the measurement needs to be graphically validated after acquisition, and in technical-forensic surveys.
Further reading: DakView™ for A-Scan and B-Scan analysis.
Datalogger
Internal instrument memory dedicated to storing measurements (and, on advanced models, the related A-Scan and B-Scan waveform), organised in files with a sequential or grid structure and sized to cover entire inspection campaigns. On Dakota models of the “-DL” family the typical capacity is 4 GB with a USB-C compatible file system, enough to store over 200,000 readings in 1,000 batches. The datalogger eliminates paper transcription errors, allows trend analysis on CMLs and enables automatic reporting via DakMaster™. It is now a de facto requirement for qualified API, AWS and ASME inspections.
Further reading: Data logger vs manual recording, DakMaster™.
Delay line tip
Interchangeable tip in plastic (acrylic) or graphite screwed onto the face of the single element transducer, which introduces a known path between the piezoelectric crystal and the surface of the material, separating the interface echo from the back-wall echo in time. It is indispensable for measuring very thin thicknesses (fractions of a millimetre), for high-temperature applications (the delay line protects the transducer from heat) and for Plastic Mode (Interface-Echo) on plastic materials. Dakota delay lines are available in standard, high-temperature and extended versions, compatible with all precision transducers.
Further reading: Delay line tips for precision transducers, Plastic Mode.
DGS – Distance Gain Size
Flaw evaluation method that relates the echo amplitude to the distance travelled and to the equivalent size of an ideal circular reflector (Equivalent Reflector Size, ERS). DGS curves are characteristic of the specific probe and are supplied by the manufacturer or reconstructed from the transducer data: they make it possible to estimate the size of an internal flaw without resorting to complex calibration reflectors. DGS is a method recognised by EN ISO 11666 and by numerous aerospace specifications; on the Dakota FX70-DL and FX81-DL flaw detectors it is integrated in the flaw evaluation toolkit, alongside DAC and TCG.
Further reading: Flaw detectors, FX70 vs FX81.
Defect / discontinuity
Internal or surface discontinuity of the material (crack, inclusion, lack of fusion, porosity, delamination) that generates a reflection of the ultrasonic wave different from the back-wall echo. The distinction between “discontinuity” (any detectable anomaly) and “defect” (a discontinuity exceeding the acceptance criteria of the applicable standard) is formally provided for by AWS, ASME and EN ISO. Detecting and classifying the defect requires a dedicated instrument (flaw detector) and knowledge of methods such as DAC, DGS or AWS indication rating. The difference between thickness measurement and flaw detection is discussed in the dedicated article.
Further reading: Thickness gauge vs flaw detector, Flaw detectors.
Dual element
Twin-crystal transducer, in which one element transmits and a second element receives, separated by an insulating acoustic barrier. It makes it possible to measure remaining thickness even on corroded, irregular, highly attenuating or high-temperature surfaces, where a single element would not be able to separate the interface echo from the back-wall echo. It is the standard probe of corrosion gauges: the Dakota range offers dual element probes with frequencies from 1 to 10 MHz and diameters from 3/16″ to 1″, in both standard and high-temperature versions. The HD Dual probe supplied as standard with the CX4 is a typical example.
Further reading: Transducers for corrosion gauges, How to choose the transducer.
E
Echo-Echo (EE) / ThruPaint™
Ultrasonic measuring mode in which the instrument determines the thickness of the metal from the time of flight between two successive back-wall echoes, ignoring reflections from any coating (paint, epoxy, rubber) present. It is the technique of choice for measuring the thickness of the metal alone through coatings up to 2 mm, without needing to remove them and keeping the anti-corrosion protection active. On Dakota products the mode is commercially named ThruPaint™ and is available on the CX4, CX6-DL, CX8-DL, ZX6-DL, MX1-DL, MX2-DL, CMX, CMX10-DL, PCX8-DL and on the FX flaw detectors. It is recommended for API 570 and API 653 inspections on coated piping and tanks.
Further reading: Echo-Echo and ThruPaint™, PECT, CT.
Echo-Echo Verify (EEV)
Advanced variant of the Echo-Echo mode, available on the top-of-the-range Dakota CMX and CMX10-DL, which validates the reading by comparing the relative amplitude between two successive echoes: if the parameters do not match the expected signature of a “clean” back-wall echo, the instrument flags the reading as unreliable instead of returning a potentially erroneous value. It is particularly useful on irregular surfaces, on thick or inhomogeneous coatings and in all situations where the presence of localised pitting could distort the standard EE measurement. EEV is one of the 6 modes (PE, PECT, PETP, EE, EEV, CT) of the CMX10-DL.
Further reading: Dakota CMX10-DL.
Ultrasonic elongation
Elastic elongation of a bolt tensioned by the tightening torque, measured ultrasonically as the difference between the acoustic length of the tightened fastener and that of the relaxed fastener. Ultrasonic measurement of elongation is the most accurate method for checking the actual applied tension, because it is independent of friction, lubrication, nominal diameter and thread geometry, factors that make the torque wrench an indirect and imprecise indicator (scatter of ±25-30%). The Dakota BT1-DL MiniMax and BT2-DL Max II instruments achieve accuracies in the order of 0.0001 mm with automatic temperature compensation.
Further reading: Tightening of pressure flanges, Bolt tension on wind turbines.
EN 12668-1
European standard “Non-destructive testing – Characterization and verification of ultrasonic examination equipment – Part 1: Instruments”: it specifies the characterisation and verification requirements for ultrasonic instrumentation, in particular flaw detectors. It defines parameters such as sensitivity, vertical and horizontal linearity, bandwidth, noise, stability over time and test procedures. The Dakota FX70-DL, FX71-DL and FX81-DL flaw detectors are declared compliant with EN 12668-1, with NIST and MIL-STD-45662A traceable calibration documented by an individual certificate.
Further reading: NDT standards, Flaw detectors.
EN 14127
European standard “Non-destructive testing – Ultrasonic thickness measurement”: it is the European reference for ultrasonic thickness measurement. It defines the procedure, equipment, calibration, surface conditions and required accuracy. All Dakota thickness gauges distributed by RODER SRL are declared compliant with EN 14127 with NIST-traceable calibration. American equivalent: ASTM E797; for instrument verification EN 15317 applies.
Further reading: EN 14127, ASTM E797 and EN 15317.
EN 15317
European standard “Non-destructive testing – Ultrasonic testing – Characterization and verification of ultrasonic thickness measuring equipment”: it specifies the qualification and verification requirements for equipment dedicated to ultrasonic thickness measurement. It covers parameters of accuracy, repeatability, range, resolution and thermal stability. All Dakota thickness gauges in the catalogue are qualified under EN 15317. RODER SRL periodic calibration includes full verification to this standard with the issue of a traceable certificate.
Further reading: NDT standards, Support and calibration.
EN 4179
European aerospace standard governing the qualification and certification of personnel performing non-destructive testing in the aeronautical sector, substantially equivalent to the American NAS 410. It establishes requirements for training, examination, experience and recertification of Level 1, 2 and 3 personnel in the UT, RT, PT, MT, ET and VT methods. Coded inspections on structural components in aluminium or titanium (for example in the NADCAP field) require EN 4179 / NAS 410 qualified operators and traceable instrumentation such as the Dakota PMX Precision Thickness Gauges series.
Further reading: NDT in aerospace, NADCAP.
F
Fastener
English term generically indicating the threaded connecting element (bolt, screw, tie rod, stud, pin) subjected to controlled tightening. In bolt tension monitoring applications the fastener is the subject of the ultrasonic elongation measurement: its geometry, length, material and end finish affect the quality of the acoustic signal and the calibration procedure. The Dakota range covers fasteners from a few centimetres (BT1-DL MiniMax) up to 30-metre tie rods (BT2-DL Max II) typical of offshore and nuclear applications.
Further reading: Transducers for bolt tension monitors, Dakota BT2-DL.
Flaw detector
Ultrasonic instrument dedicated to detecting, locating and classifying internal or surface discontinuities in materials. Unlike the thickness gauge, which returns the numerical value only, the flaw detector shows the complete A-Scan as its primary display and integrates flaw evaluation functions such as DAC, TCG, DGS, AWS indication rating, multiple gates and management of angled wedges. The Dakota range includes the portable FX70-DL/FX71-DL and the benchtop FX81-DL, both compliant with EN 12668-1, equipped with an integrated AWS D1.1 toolkit and a 4 GB datalogger.
Further reading: Flaw detectors, Thickness gauge vs flaw detector.
Forging
Metal component obtained by hot plastic deformation, in which the crystalline grain is oriented and refined. UT inspections on forgings look for discontinuities typical of the process (cooling cracks, elongated inclusions, segregations) using flaw detectors with longitudinal contact probes and, for complex areas, shear wave probes on a wedge. Inspection specifications refer to ASTM A388, EN 10228 and to sector procedures (oil & gas, aerospace, railway). The Dakota FX70-DL and FX81-DL flaw detectors are suitable for these applications.
Further reading: Flaw detectors.
Probe frequency
Nominal frequency (in MHz) of the piezoelectric crystal of the transducer: it determines resolution, penetration depth and the minimum detectable size of discontinuities. High frequencies (10–25 MHz) offer high resolution on thin thicknesses and low-attenuation materials (aluminium, titanium, sheet metal); low frequencies (1–2 MHz) guarantee greater penetration in attenuating materials such as cast irons, composites and thick plastics. The Dakota range covers from 1 MHz to 25 MHz on dual and single element probes, in addition to shear wave probes for welds from 2 to 5 MHz on standard wedges.
Further reading: How to choose the transducer, Probes and accessories.
G
Gain
Amplification of the received signal applied by the instrument, expressed in dB. Too low a gain can leave weak flaw echoes hidden; too high a gain saturates the display, reduces the signal-to-noise ratio and can generate spurious readings. The gain value is set during calibration on the reference reflector (for example the back-wall echo of the block) and possibly modulated by AGC and TCG during scanning. The Dakota FX70-DL and FX81-DL flaw detectors offer up to 110 dB of gain with AGC; the CMX10-DL combines 110 dB of gain with AGC and a 100 MHz single-shot digitiser.
Further reading: AGC, TCG, Dakota CMX10-DL.
Grid batching and grid file
Data storage mode in the internal datalogger organised as a two-dimensional grid, in which each cell corresponds to a measuring point identified by coordinates (row, column). It is the typical structure of API 653 inspections on tank shells and of periodic piping mappings: it facilitates comparison between successive campaigns and the identification of areas with an anomalous corrosion rate. On the Dakota MX1-DL and MX2-DL models the grid file can reach 999×52 in size with over 225,000 storable readings. The alternative structure is the sequential file, organised in a linear sequence.
Further reading: Dakota MX1-DL, API 653 tank inspection.
H
High Penetration
Category of ultrasonic thickness gauges designed for applications on highly attenuating materials, where conventional instruments cannot obtain reliable back-wall echoes. They are characterised by high transmission energy, a low-noise receiver and support for low-frequency probes (1–2 MHz). They are dedicated to carbon-fibre or fibreglass composites, thick plastics, rubbers, grey cast iron castings and coarse-grained alloys. The Dakota PMX4-DL High Penetration is the Dakota reference for this category, with an extended datalogger and A-Scan for visual validation.
Further reading: Dakota PMX4-DL, Composites.
High Temperature transducer
Transducer sized for measurements on surfaces at high temperature (typically up to 400–500 °C continuously, with dedicated probes up to 540 °C in intermittent measurement). The active element, the encapsulation and the delay line are made of thermally stable materials; the use of a high-temperature couplant is mandatory. Dakota HT probes cover online inspections of in-service piping, pressure vessels and process plants where shutting down the asset is not acceptable.
Further reading: How to choose the transducer, High-temperature couplants.
I
Indication rating (AWS)
Numerical index, expressed in dB, defined by AWS D1.1 for evaluating the indications detected during UT weld inspection. It is calculated by subtracting from the gain level at which the indication echo reaches 80% of FSH (Full Screen Height) the contributions of reference gain, attenuation and position, and is compared with the acceptance table of the standard to establish whether the discontinuity is to be accepted or rejected. The Dakota FX70-DL/FX71-DL and FX81-DL flaw detectors integrate an AWS toolkit that automatically performs the calculation from the calibration parameters, reducing the risk of interpretation error.
Further reading: AWS D1.1: requirements, AWS D1.1 inspection with the FX70-DL.
IP65
Degree of protection defined by the IEC 60529 standard: the digit “6” indicates total protection against dust, the digit “5” protection against low-pressure water jets from any direction. It is the minimum level of ruggedness expected of a thickness gauge intended for field use, where industrial dust, water and mist are common. All Dakota portable thickness gauges of the ZX, CX, MX, CMX and PMX series meet IP65; for underwater applications a dedicated instrument is required.
Further reading: Thickness gauges, Industrial applications.
Pulse-Echo (PE)
Fundamental physical principle of ultrasonic thickness measurement: the instrument emits a short ultrasonic pulse, which travels through the material, is reflected at the opposite interface (back-wall echo) and returns to the transducer. By measuring the time of flight and knowing the sound velocity in the material, the instrument calculates the thickness. It is the basic mode available on all Dakota thickness gauges: economical, fast, reliable on homogeneous materials and uncoated surfaces. To handle coatings, the EE, PECT, PETP or CT modes are used depending on the need.
Further reading: How ultrasonic measurement works, Dakota CX2.
Coded inspection
Inspection conducted according to a written specification (code, standard, qualified company procedure) that imposes traceability of instrument, probe, calibration, qualified operator and archiving of raw data. Typical examples: UT weld inspection to AWS D1.1 or EN ISO 17640, CML monitoring on in-service piping to API 570, inspection of pressure flanges to ASME PCC-1. Coded inspection requires instruments with a datalogger, recordable A-Scan or B-Scan and management of multiple setups; on Dakota “-DL” models these requirements are integrated.
Further reading: Data logger and coded inspection, When the A-Scan is needed.
M
Grid mapping
Inspection technique in which thickness is surveyed on a predefined grid of points on the surface of the asset, with constant horizontal and vertical pitch. It returns a two-dimensional representation of the state of thinning and makes it possible to identify areas of pitting, crevice corrosion or localised erosion. Mapping is mandatory for API 653 inspections on tank shells and strongly recommended by API 570 for critical piping. The Dakota MX1-DL, MX2-DL and CMX gauges store the grid in a grid file with dimensions up to 999×52 and support automatic export to DakMaster™.
Further reading: Thickness measurement of pipes and piping, Tank inspection.
MIL-STD-45662A
American military standard “Calibration System Requirements”, which defines the requirements of the calibration system for measuring instrumentation used on supplies to the US Department of Defense. Superseded by ANSI/NCSL Z540 but still cited as a historical traceability reference. All Dakota instruments distributed by RODER SRL are declared NIST and MIL-STD-45662A traceable: periodic calibration performed by the in-house laboratory produces a certificate documenting both traceabilities.
Further reading: Traceability, RODER SRL support and calibration.
Multi-Echo
Measuring mode that uses a sequence of successive back-wall echoes to validate and refine the thickness value: the instrument accepts the reading only if several consecutive echoes are consistent, automatically discarding spurious measurements due to poor coupling or surface inclusions. It drastically reduces false readings in fast scans on irregular or coated surfaces. On Dakota products the Multi-Echo mode is characteristic of the ZX6-DL model, where it is combined with Echo-Echo ThruPaint™ for measurements through epoxy coatings.
Further reading: Dakota ZX6-DL.
N
NADCAP
National Aerospace and Defense Contractors Accreditation Program: global accreditation programme for special suppliers in the aerospace and defence sector, managed by PRI (Performance Review Institute). To obtain NDT accreditation, the supplier must demonstrate compliance with written procedures, personnel training (NAS 410 / EN 4179), traceable instrumentation and data archiving. The Dakota PMX series, with 0.001 mm resolution, A-Scan and NIST-MIL-STD-45662A calibration, is compatible with the typical requirements of a NADCAP UT audit.
Further reading: NDT in aerospace, EN 4179.
NIST
National Institute of Standards and Technology: standards body of the United States Department of Commerce, which provides the primary reference standards for world metrology. The NIST traceability of measuring instrumentation means that its calibration can be traced through documented comparisons to a primary standard held by NIST: it is the basic requirement for using the instrument in API, ASME and AWS coded inspections and in general throughout the industrial world. All Dakota thickness gauges and flaw detectors distributed by RODER SRL are NIST and MIL-STD-45662A traceable.
Further reading: Traceability, Support and calibration.
Nodularity (test)
Ultrasonic test used in foundries to estimate the degree of nodularity of the graphite in spheroidal cast irons, based on measuring the sound velocity in the material: high nodularity corresponds to a higher velocity, close to that of pure cast iron. The Velocity Mode of the Dakota CX6-DL, CX8-DL and ZX6-DL thickness gauges allows the test to be performed directly in the workshop on known specimens, providing non-destructive quality control before the castings are put into service.
Further reading: Dakota ZX6-DL.
P
Dakota Part Number
Unique code assigned by Dakota NDT to each commercial configuration of instrument, probe, accessory or document. Instrument part numbers follow the format Z-xxx-xxxx (for example Z-313-0001 for the CX8-DL), probe part numbers a dedicated format for each family. For a correct purchase it is essential to quote the exact P/N: under the same trade name there may be variants with different probes, cables or blocks. RODER SRL manages orders by the official Dakota P/N; the complete inventory can be consulted from the product pages.
Further reading: Product catalogue, Request a quote.
PECT – Pulse-Echo Coating Through
Proprietary Dakota measuring mode available on the CMX and CMX10-DL models, which returns in a single reading both the thickness of the coating and the thickness of the underlying metal, while retaining the ability to detect pitting and localised flaws. It combines the advantages of standard Pulse-Echo (sensitivity to local flaws) with those of Echo-Echo ThruPaint™ (ability to read the metal through coatings). It is the mode of choice for corrosion-under-coating (CUI) inspections in protected piping and tanks, where both the remaining metal value and coating monitoring are needed.
Further reading: What PECT mode is, Dakota CMX Series.
PETP – Pulse-Echo Through Paint
Measuring mode available on the Dakota CMX10-DL as one of the 6 modes (PE, PECT, PETP, EE, EEV, CT). It is a variant of Pulse-Echo managed for coated surfaces, in which the instrument specifically processes the echo from the metal substrate while maintaining the flaw sensitivity typical of PE. It is useful in intermediate scenarios between pure PE and Echo-Echo, where the coating is thin or inhomogeneous and classic PE mode would generate readings at the coating-metal interface. For the specific operating parameters refer to the CMX10-DL operating manual: its correct selection depends on the surface conditions and the type of coating.
Further reading: Dakota CMX10-DL, Echo-Echo.
Pencil probe
Elongated, small-diameter transducer resembling a pen, dedicated to the inspection of narrow or hard-to-reach geometries (weld throats, heat-exchanger fins, internal radii). The compact shape reduces the contact area and allows precise positioning even in areas impossible for a standard probe. The Dakota CMX10-DL range supports pencil probes in addition to dual, single and delay probes, managed through the multi-way ODU Smart Port connector.
Further reading: Dakota CMX10-DL, How to choose the transducer.
Pitting
Form of localised corrosion that appears as small-diameter but deep craters in the wall of the material. Pitting is particularly insidious because it can lead to wall perforation with minimal overall mass loss and therefore be underestimated by a spot measurement. Its detection requires A-Scan and B-Scan: only waveform analysis makes it possible to distinguish a back-wall echo from a pit echo, while the B-Scan shows its extent along the scanning path. The Dakota MX2-DL, CMX10-DL and PCX8-DL models are particularly suitable for detecting pitting.
Further reading: Corrosion, Dakota MX2-DL.
Plastic Mode (Interface-Echo)
Measuring mode optimised for plastic materials and rubbers, in which the thickness reading is taken between the interface echo generated by the delay line and the first back-wall echo in the material. It compensates for the low sound velocity and high attenuation typical of plastic, PVC, polyethylene and PTFE: without Plastic Mode the standard reading would fail or would require manual velocity corrections. It is available on the Dakota PMX, PZX1-DL and PCX8-DL precision gauges in combination with dedicated delay line tips.
Further reading: Delay line tips, Dakota PMX2-DL / PMX3-DL.
PRF – Pulse Repetition Frequency
Frequency at which the instrument emits ultrasonic pulses into the material, expressed in Hz. A high PRF increases the number of readings per second in fast scans but can generate spurious echoes (ghost echoes) if the next pulse is emitted before the echoes of the previous one have completely attenuated in the material. The PRF must therefore be matched to the inspection depth and to the sound velocity in the material. On the Dakota MX1-DL and MX2-DL models the PRF reaches 250 Hz, supporting the fast scan mode required by API 653 mappings.
Further reading: Dakota MX1-DL, Scan Mode.
R
Measuring range
Interval of thicknesses measurable by the instrument, declared in the technical specifications and dependent on the probe used, the material and the mode (PE, EE, PECT). Examples: the Dakota CX2 has a range of 0.63–500 mm on steel in PE; the PMX4-DL High Penetration extends coverage on highly attenuating materials; the bolt tension monitors cover from a few centimetres (BT1-DL) to 30 m (BT2-DL). Checking that the range of the chosen model covers the application, including coating margins where relevant, is the first step in selecting the instrument.
Further reading: Thickness gauges, CX2 / CX4 / CX8 comparison.
Corrosion rate and remaining life
The corrosion rate is the speed at which the wall of an asset thins over time, typically expressed in mm/year or mils/year. It is calculated from the difference between thickness measurements taken at the same CML at successive times, divided by the time interval. Knowing the design thickness, the minimum allowable thickness (Tmin) and the corrosion rate, the remaining life of the asset is calculated as the number of years separating the last measurement from reaching Tmin. The API 570 and API 653 standards prescribe this calculation methodology: the Dakota CMX, MX and CMX10-DL instruments, integrated with DakMaster™, automate trend analysis on CMLs.
Further reading: Monitoring uniform corrosion, API 570 / 653.
Resolution
Smallest variation in thickness that can be displayed on the instrument’s screen. It should not be confused with accuracy, which is a broader metrological parameter: resolution expresses only the reading “step”, not the error. On Dakota corrosion gauges the typical resolution is 0.01 mm; on precision gauges (PMX, PCX, PZX1-DL) it goes down to 0.001 mm. On the BT1-DL and BT2-DL bolt tension monitors the elongation reading resolution is in the order of 0.0001 mm. The actually useful resolution is limited by the accuracy of the instrument and by the operating conditions.
Further reading: Dakota PMX2-DL / PMX3-DL.
Coating
Protective layer applied to the surface of the metal (paint, epoxy, rubber, polymer, galvanising) for anti-corrosion, aesthetic or functional purposes. From the point of view of ultrasonic inspection, the presence of a coating alters the standard PE reading: to read the metal thickness correctly, the Echo-Echo (ThruPaint™), PECT or PETP modes must be used. CT mode returns the coating thickness only. Operating decisions depend on the thickness and composition of the coating: ThruPaint™ is effective up to about 2 mm.
Further reading: Echo-Echo and ThruPaint™, PECT.
S
Weld
Joint made by localised fusion of the base materials (with or without filler material) and the adjacent heat-affected zone. Welds are one of the main targets of non-destructive testing because they typically concentrate the critical design points of the component: lack of fusion, lack of penetration, cooling cracks, porosity, slag inclusions. UT inspection is performed with shear wave probes on a wedge (45°, 60°, 70°) to AWS D1.1, EN ISO 17640 or ASME Section V. The Dakota FX70-DL/FX71-DL and FX81-DL flaw detectors fully cover these applications.
Further reading: AWS D1.1: requirements, UT inspection with the FX70-DL.
Scan Mode
Fast acquisition mode in which the instrument performs a continuous sequence of readings as the transducer passes over the surface, at a high rate (typically 16, 100, 200 or 250 readings per second depending on the model). Scan mode shows in real time the minimum, maximum and average value during the pass and is the mode of choice for API 653 mappings and for quickly finding the point of minimum thickness on piping or tanks. On the Dakota MX1-DL and MX2-DL gauges scan mode reaches 200 readings/second; on the CMX10-DL it is combined with live waveform storage at 60 Hz.
Further reading: Measurement of pipes and piping.
Sequential file
Linear storage structure in the datalogger, in which readings are stored in progressive sequence without a grid constraint. It is the quickest mode to configure and is suitable for inspection campaigns where no formal mapping is planned, such as spot sampling in goods receiving or random checks in production. On Dakota “-DL” models the sequential structure coexists with grid files, and the user can choose the mode best suited to each inspection setup.
Further reading: Grid batching, Datalogger.
Setup utente
Preset configuration of parameters (probe, material, measuring mode, gain, gate, calibration, units) saved in the instrument and recallable in a single step. It allows rapid switching from one inspection to another without manually reconfiguring the instrument, reducing the risk of error. The Dakota MX1-DL and MX2-DL models manage up to 64 user setups; the CMX10-DL and the FX flaw detectors integrate an extended library of factory setups for standard materials. Good operating practice is to create dedicated setups for each asset or coded inspection procedure.
Further reading: Dakota MX1-DL.
Shear wave
Ultrasonic wave propagation mode in which the particles of the medium oscillate perpendicular to the direction of propagation, rather than parallel as in longitudinal waves. Shear waves are obtained by refraction on an angled wedge and are fundamental in weld inspection, where they make it possible to intercept planar defects parallel to the surface of the joint, undetectable with direct-contact longitudinal waves. The Dakota range of shear wave transducers includes quick-change and standard models, paired with 45°, 60° and 70° transducer wedges for compliance with AWS D1.1 and EN ISO 17640.
Further reading: Transducers for flaw detectors, Wedge.
Single element
Transducer with a single piezoelectric crystal performing both the transmitting and receiving functions. It offers the highest resolution and the “cleanest” A-Scan on homogeneous materials and uncorroded surfaces; it is the standard probe of precision gauges. The Dakota single element range covers frequencies of 2–25 MHz with contact, delay line and high temperature versions, sized for inspections on thin sheet, aluminium, titanium, glass and plastic. For corroded or highly attenuating surfaces the dual element probe is preferred instead.
Further reading: Transducers for precision gauges, Selection guide.
Ultrasonic probe (transducer)
Component that converts an electrical pulse into a mechanical ultrasonic wave (and vice versa the return signal) by means of a piezoelectric crystal. It is the heart of the measuring chain: its frequency, bandwidth, active element dimensions and delay line geometry determine resolution, penetration depth and flaw sensitivity. The Dakota probes distributed by RODER SRL cover all ultrasonic measurement needs: dual element for corrosion, single element for precision, delay line for thin thicknesses, shear wave for welds, high temperature, underwater and low frequency for difficult materials.
Further reading: Probes and accessories, How to choose the transducer.
Sonic Tester
Line of Dakota ultrasonic instruments dedicated to motorsport and engine tuners for measuring the thickness of engine cylinder walls before and after boring, decking or liner replacement work. It includes the basic R9 model and the top-of-the-range RX8-DL with colour A-Scan, integrated datalogger and dedicated cylinder wall mapping functions. NIST-MIL-STD traceable calibration guarantees the repeatability of the surveys that is indispensable in racing, where tolerances of a few hundredths of a millimetre make the difference between compliance and out-of-specification.
Further reading: Special instruments, Engine cylinder wall measurement.
Ultrasonic thickness gauge
Portable or benchtop ultrasonic instrument dedicated to measuring the thickness of metal, plastic or composite walls using the pulse-echo contact method. It is the most widespread NDT instrument in corrosion inspections on pipelines and tanks, in quality control at goods receiving, in fleet and plant maintenance. The Dakota range distributed by RODER SRL covers 14 models, from the entry-level CX2 to the top-of-the-range CMX10-DL and PCX8-DL, with or without A-Scan, with or without datalogger, with or without ThruPaint™ mode.
Further reading: Thickness gauges, Basic model comparison.
Step block
Stepped calibration block, in which a single artefact presents several certified thicknesses in a “staircase” (e.g. 2.5 / 5 / 7.5 / 10 / 12.5 mm). It allows 2-point calibration over a wide range to be performed quickly, without having to change the block between the two readings. All Dakota step blocks are in 4340 steel, certified with ±1% tolerance and accompanied by a traceable calibration certificate. They are the calibration standard for coded inspections of piping and tanks.
Further reading: Calibration blocks, Calibration.
T
TCG – Time Corrected Gain
Function that applies a gain variable over time (and therefore with depth) to the A-Scan, compensating for material attenuation and beam divergence: two echoes of the same size at different depths appear with the same amplitude on the display, simplifying flaw evaluation over the whole inspection range. TCG is a standard function of the Dakota FX70-DL/FX71-DL and FX81-DL flaw detectors and is combined with DAC and DGS in the flaw evaluation toolkit for AWS D1.1, ASME Section V and EN ISO 11666.
Further reading: Dakota FX70-DL, DAC.
Traceability (NIST / MIL-STD)
Documented chain of comparisons linking the calibration of a measuring instrument to an internationally recognised primary standard (generally NIST or a national equivalent). Traceability is the metrological foundation for using the instrument in coded inspections: without traceability the data collected cannot be relied upon in audits, certifications or technical disputes. RODER SRL periodic calibration produces a NIST and MIL-STD-45662A traceable calibration certificate attesting compliance with EN 14127, EN 12668-1, EN 15317 and ASTM E797 depending on the model.
Further reading: Support and calibration, NIST, MIL-STD-45662A.
TRIG
Advanced digital trigger mode present on the Dakota CMX10-DL, enabled in flaw prove-up: the instrument automatically identifies the starting point of the echo of interest on the A-Scan according to configurable criteria (peak, zero crossing, threshold), guaranteeing stable readings even in the presence of pitting or intermediate echoes that would confuse a standard trigger. Combined with 16-point DAC, TRIG extends the CMX10-DL thickness gauge to evaluation functions typical of a basic flaw detector.
Further reading: Dakota CMX10-DL.
Piping (pipeline)
Hollow cylindrical component intended for transporting pressurised fluids (hydrocarbons, steam, water, technical gases). Piping is one of the main assets subject to periodic UT inspection: internal corrosion, corrosion under insulation (CUI) and erosion are the main damage mechanisms. Inspections are governed by API 570 (in service) and by the applicable construction standards (ASME B31.x, EN 13480), with methodologies based on CMLs, ThruPaint™ and grid mapping. The Dakota CX8-DL, CMX, MX1-DL, MX2-DL and CMX10-DL instruments are the typical references for these applications.
Further reading: Measurement of pipes and piping, Pipeline inspection to API 570.
U
Ultrasound
Acoustic waves with a frequency above the limit audible to humans (conventionally >20 kHz). In industrial NDT, frequencies typically between 0.5 and 25 MHz are used: the beam is generated by the piezoelectric effect from a crystal inside the transducer, travels through the material as a longitudinal or transverse elastic wave and is reflected by every acoustic impedance discontinuity (interfaces, flaws, back wall). Ultrasonic thickness measurement (UT thickness) and flaw detection (UT flaw detection) techniques are the technological pillar of the Dakota catalogue distributed by RODER SRL.
Further reading: Principles of ultrasonic measurement, About us.
Underwater transducer
Waterproof transducer sized for underwater measurements, typically for the inspection of ship hulls, offshore structures, subsea pipelines and port infrastructure. The probe is designed to withstand the hydrostatic pressure of the declared operating depths (generally up to several tens of metres) and to guarantee stable acoustic coupling when submerged. Underwater inspections require a dedicated water-resistant instrument with a datalogger, so that the data can be analysed after the dive via DakView™.
Further reading: DakView™.
USB-C
Universal connectivity standard which, on the most recent Dakota models (CMX10-DL, MX1-DL, MX2-DL), directly implements a file system accessible from the computer. The instrument appears as a mass storage unit: data can be downloaded without dedicated drivers, copied by drag-and-drop and processed on DakMaster™. This architectural choice drastically simplifies campaign workflows compared with the proprietary protocols of the past and aligns with modern industrial interoperability standards.
Further reading: Dakota MX2-DL, DakMaster™.
V
Sound velocity
Speed at which the ultrasonic wave propagates in the material, expressed in m/s. It is an intrinsic characteristic of the material and depends on density and modulus of elasticity: for example, carbon steel has a longitudinal velocity of about 5920 m/s, aluminium about 6320 m/s, water 1480 m/s. Accurate knowledge of the velocity is a prerequisite for converting time of flight into thickness: every Dakota gauge has a library of preset standard materials and the Velocity Mode function to determine the velocity on specimens of known thickness. An incorrect velocity generates a proportional error in the thickness measurement.
Further reading: Principles of ultrasonic measurement, Velocity Mode.
Velocity Mode
Operating mode in which the instrument determines the sound velocity of an unknown material from a specimen of known thickness. It makes it possible to extend the use of the thickness gauge to alloys and materials not present in the factory library and to perform nodularity tests on spheroidal cast irons in the foundry. It is available on the Dakota CX6-DL, CX8-DL, ZX6-DL, MX and CMX models. Correct determination of the velocity in Velocity Mode is a prerequisite for accurate measurements on special materials and is part of good calibration practice for new purchases.
Further reading: Dakota CX6-DL, Nodularity test.
Notes on use
The glossary is updated on the basis of the content published on ultrasuonindt.it and the official Dakota NDT documentation. For application details on the individual sectors, see the Applications page; for choosing the instrument, see the Products page and the comparisons published in the News section; for calibration, training and technical support requests, see the Support page. For any technical question not covered by the entries above, the RODER SRL team is available through the Contact page.
Suggestions, additions or reports of missing terms are welcome: the glossary is intended as a living reference, to be enriched as the site expands with new technical guides and product pages.