Course Title

Day 1 — Acoustic Physics, Transducers, and Instrument Fundamentals

1. Introduction to Ultrasonic Testing

1.1 UT Overview and Standards

• UT detects internal and surface-breaking discontinuities by introducing high-frequency sound waves into a material.

• UT applications — weld inspection, thickness measurement, lamination detection, corrosion mapping, and flaw sizing.

• ISO 9712:2021 — Level I performs under supervision; Level II evaluates, interprets, and signs UT reports independently.

• ASNT SNT-TC-1A — employer-based qualification with defined training hours, experience, and examination requirements.

• UT advantages — volumetric, portable, real-time, and capable of precise flaw sizing and location.

• UT limitations — requires couplant, surface condition sensitivity, and skilled interpretation of A-scan displays.

1.2 Acoustic Physics

• Longitudinal waves — compression waves where particle motion is parallel to the direction of wave propagation.

• Shear waves — transverse waves where particle motion is perpendicular to the direction of propagation.

• Surface waves — Rayleigh waves — travel along the surface and are used for surface-breaking flaw detection.

• Lamb waves — plate waves used for thin material and large-area scanning applications.

• Sound velocity — varies by material and wave mode — longitudinal waves travel faster than shear waves in the same material.

• Acoustic impedance — Z = material density × sound velocity — determines reflection and transmission at interfaces.

• Reflection — sound reflects at an interface where acoustic impedance changes — the basis of flaw detection.

• Refraction — sound changes direction when crossing a boundary between materials of different acoustic velocities.

• Mode conversion — a longitudinal wave incident at an angle produces both reflected and refracted longitudinal and shear waves.

• Snell's Law — governs the relationship between incident and refracted wave angles at an interface.

2. Transducers and Probes

2.1 Transducer Types

• Piezoelectric element — converts electrical energy to mechanical vibration and vice versa — the heart of the UT probe.

• Single element straight beam probe — used for longitudinal wave straight beam inspection and thickness measurement.

• Dual element — TR — probe — separate transmitting and receiving elements — better near-surface resolution.

• Angle beam probe — wedge-mounted element producing a refracted shear wave at a defined angle in the test material.

• Common angle beam angles — 45°, 60°, and 70° — selected based on weld geometry and material thickness.

• Immersion probe — used in water-coupled immersion testing for automated scanning applications.

• Wheel probe — liquid-filled wheel coupling the probe to the surface for high-speed automated scanning.

2.2 Probe Characteristics

• Frequency — higher frequency produces shorter wavelength and better resolution but less penetration.

• Typical UT frequencies — 1 MHz to 10 MHz for industrial weld and material inspection.

• Near field — the region close to the probe face where sound pressure fluctuates — unreliable for flaw detection.

• Far field — beyond the near field — where sound pressure decreases predictably and inspection is reliable.

• Beam divergence — the spread of the sound beam beyond the near field — increases with lower frequency.

• Dead zone — the blind zone immediately beneath the probe face where near-surface flaws may not be detected.

• Probe index point — the point on the probe shoe directly above the beam exit — used for flaw location measurement.

• Probe verification per ASTM E1065 — verifying probe performance characteristics before use.

3. UT Instrument and Display

• Pulse-echo instrument — generates electrical pulses, receives echo signals, and displays them on an A-scan.

• A-scan display — amplitude versus time display showing the initial pulse, echoes, and their relative positions.

• B-scan — cross-sectional view of the material showing flaw depth and through-thickness position.

• C-scan — plan view of the scanned area showing flaw location and extent in two dimensions.

• Time base — the horizontal axis of the A-scan representing the time of flight of the sound pulse.

• Gain — controls the amplification of received signals — set during calibration and not changed during scanning.

• Gate — a time window on the A-scan that monitors a defined depth range for echo signals.

• Alarm threshold — the amplitude level within the gate that triggers an indication alarm.

• Couplant — liquid or gel medium between probe and surface ensuring sound transmission — water, gel, or oil.

Day 2 — Calibration, Straight Beam Inspection, and Angle Beam Inspection

4. Reference Blocks and Calibration

4.1 Reference Blocks

• Reference blocks contain machined reflectors of known size and depth for instrument calibration.

• IIW — International Institute of Welding — block — the standard calibration block for angle beam weld inspection.

• ASME Basic Calibration Block — contains side-drilled holes — SDH — used for DAC curve construction per ASME Section V.

• Side-drilled holes — cylindrical reflectors used as reference targets for DAC curve construction.

• Flat-bottom holes — used as reference reflectors for straight beam examination calibration.

• Reference block material — must match the acoustic velocity of the test material per ASTM E428.

• Reference block certification — dimensions, material, and surface condition documented and verified.

4.2 Instrument Calibration Procedures

• Time base calibration — setting the A-scan horizontal scale to represent a known material depth range.

• Straight beam calibration — using the IIW block or step wedge to set the time base for longitudinal wave inspection.

• Angle beam calibration — using the IIW block to verify beam angle, determine probe index point, and set the time base.

• Sensitivity calibration — setting the reference gain level using the specified reference reflector in the calibration block.

• DAC — Distance Amplitude Correction curve — plots the amplitude response of side-drilled holes at multiple depths.

• DAC construction — plotting at least three SDH responses at different depths and drawing the correction curve.

• Transfer correction — compensating for surface condition differences between the reference block and the test specimen.

• Calibration frequency — at the start of each examination, every four hours, and when the equipment is disturbed.

5. Straight Beam Pulse-Echo Inspection

5.1 Thickness Measurement

• Straight beam thickness measurement — measuring wall thickness from one surface using pulse-echo time of flight.

• Thickness formula — T = (velocity × time of flight) ÷ 2.

• Corrosion mapping — scanning a defined grid pattern to measure remaining wall thickness at each grid point.

• Minimum grid spacing — determined by the size of the smallest reportable corrosion patch required by the procedure.

• B-scan thickness profiling — generating a cross-sectional thickness profile during corrosion scanning.

• Couplant consistency — variation in couplant thickness affects time of flight and introduces measurement error.

5.2 Lamination and Plate Inspection

• Lamination — a planar discontinuity parallel to the plate surface — detected as a full back wall loss or intermediate echo.

• Lamination inspection scan pattern — overlapping scan lines at 10% minimum overlap per ASME Section V.

• Maximum scan speed — 150 mm/s — the maximum hand scanning speed permitted per ASME Section V to avoid missed flaws.

• Back wall echo loss — a reduction in back wall echo amplitude indicating an intermediate reflector such as a lamination.

• Forgings inspection per ASTM E388 — straight beam examination for forging flaws including pipe, bursts, and segregations.

6. Angle Beam Shear Wave Weld Inspection

6.1 Beam Path and Sound Path Geometry

• Angle beam probe — generates a refracted shear wave in the test material at a defined refracted angle.

• Refracted angle verification — confirmed on the IIW block before each examination session.

• Skip distance — the surface distance from the probe index to the point where the beam completes one full V-path.

• Half skip — the surface distance from the probe to the beam's deepest point at the far wall of the material.

• Beam path calculation — used to determine the probe position required to direct the beam at a specific weld zone.

• Flaw location — calculated from the A-scan time of flight reading using the beam angle and material velocity.

6.2 Weld Scanning Procedures

• Weld preparation — parent metal must be scanned for laminations before angle beam weld inspection begins.

• Scanning coverage — the entire weld volume must be covered — using multiple probe positions from both sides.

• Scan pattern — forward-backward movement combined with lateral indexing to achieve full weld volume coverage.

• Maximum scan speed — 150 mm/s per ASME Section V Article 4.

• Probe index overlap — minimum 10% overlap of the transducer dimension perpendicular to the scan direction.

• Probe angle selection — 45° for thick sections, 60° for medium, and 70° for thin sections or shallow flaw detection.

• Tandem technique — two probes used together — one transmitting, one receiving — for vertical planar flaw detection.

• Weld inspection per ISO 17640: Non-Destructive Testing of Welds — Ultrasonic Testing — scan coverage requirements.

Day 3 — Flaw Detection, Sizing, and Acceptance Criteria

7. Flaw Detection and A-Scan Interpretation

7.1 Flaw Signal Identification

• Flaw echo — an intermediate signal between the initial pulse and back wall echo indicating a reflector within the material.

• Signal amplitude — related to reflector size, orientation, and distance from the probe.

• Signal position on the time base — indicates the depth or sound path length to the reflector.

• Distinguishing flaw echo from geometry echo — structural features produce echoes at fixed, predictable locations.

• Flaw characterization — planar flaws produce sharp, high-amplitude signals; volumetric flaws produce lower, broader signals.

• Signal dynamics — how the signal amplitude changes as the probe moves relative to the reflector aids characterization.

7.2 Flaw Location

• Surface distance — calculated from the A-scan sound path and probe angle using trigonometry.

• Depth — calculated from the A-scan sound path reading and the probe refracted angle.

• Flaw marking — the flaw position is marked on the test surface for reporting and later access.

• Position accuracy — affected by beam spread, probe index point accuracy, and time base calibration.

8. Flaw Sizing Techniques

8.1 Amplitude-Based Sizing

• DAC — Distance Amplitude Correction curve method — comparing flaw echo amplitude to the DAC curve at the same depth.

• Recording level — typically 20% DAC or 50% DAC — flaws below the recording level are noted but may not require sizing.

• Evaluation level — flaws above the evaluation level are assessed against acceptance criteria.

• Rejection level — flaws above the rejection level are automatically rejectable regardless of size assessment.

• 6 dB drop method — the probe is moved until the signal drops 6 dB below the peak — the probe span defines flaw length.

• 20 dB drop method — the probe is moved until the signal drops 20 dB — used for flaw edge definition in some codes.

8.2 Tip Diffraction Sizing

• Tip diffraction — sound diffracts from the tips of planar discontinuities — enabling height sizing without amplitude comparison.

• Tip diffraction signals appear as low-amplitude signals beyond the main flaw reflection signal.

• Flaw height sizing — the vertical extent of the flaw is calculated from the time difference between upper and lower tip echoes.

• Tip diffraction accuracy — typically better than amplitude-based methods for planar flaws oriented perpendicular to the beam.

9. Acceptance Criteria Application

• Acceptance criteria must always be applied from the standard specified in the examination procedure.

• ISO 11666: Non-Destructive Testing of Welds — Ultrasonic Testing — Acceptance Levels — Levels 2 and 3 for welds.

• AWS D1.1 acceptance criteria — based on indication amplitude relative to the reference level and indication length.

• API 1104 acceptance criteria — length and depth limits for pipeline girth weld UT indications.

• ASME Section VIII — acceptance criteria for pressure vessel weld UT based on indication amplitude and length.

• Planar flaw — crack, lack of fusion, and incomplete penetration — evaluated by height as well as length.

• Volumetric flaw — porosity and inclusions — evaluated by amplitude relative to reference level and indication length.

• UT report — documenting flaw location, depth, sound path, amplitude relative to DAC, sizing method, and accept/reject decision.

Day 4 — Advanced UT Methods, Pipe Inspection, and Procedure Development

10. Time of Flight Diffraction

10.1 TOFD Principles

• TOFD — Time of Flight Diffraction — a technique using diffracted signals from flaw tips for precise flaw height measurement.

• TOFD uses two probes in pitch-catch configuration — one transmitter and one receiver straddling the weld.

• Lateral wave — a surface-skimming signal arriving first — used as the reference timing signal in TOFD.

• Back wall signal — arrives last — establishes the full material thickness reference.

• Diffracted signals from flaw tips appear between the lateral wave and back wall signal.

• TOFD flaw height — calculated precisely from the time difference between upper and lower tip diffraction signals.

• TOFD advantages — high sensitivity, accurate sizing, and full weld volume coverage in a single scan.

• TOFD dead zone — the region immediately below the surface where the lateral wave masks near-surface flaws.

10.2 TOFD D-Scan Interpretation

• D-scan display — a time-position image showing lateral wave, diffracted signals, and back wall across the scan length.

• Flaw identification on D-scan — a pair of curved hyperbolic arcs above and below the mid-material position.

• Flaw location — horizontal position on the D-scan indicates weld length position; vertical position indicates depth.

• TOFD combined with pulse-echo — TOFD detects and sizes flaws; pulse-echo provides amplitude-based characterization.

11. Phased Array Ultrasonic Testing

11.1 PAUT Principles

• PAUT — Phased Array Ultrasonic Testing — uses a multi-element array probe with electronic beam steering and focusing.

• Focal law — the electronic timing sequence applied to individual array elements to create a specific beam angle and focal depth.

• Electronic scanning — the beam angle is swept electronically across a defined angular range without moving the probe.

• Linear scan — the active aperture is electronically indexed along the array — equivalent to multiple probe positions.

• Sectorial scan — S-scan — the beam angle is swept through a range of angles from a fixed probe position.

• PAUT advantages — faster inspection, multiple angles in a single pass, and real-time image display.

11.2 PAUT Display and Calibration

• S-scan display — a fan-shaped image showing the weld cross-section with flaw position and depth visible directly.

• PAUT calibration — sensitivity and time base calibrated for each focal law using the appropriate reference block.

• Encoder — position encoder tracks probe movement to produce accurate B-scan and C-scan images.

• PAUT procedure validation — demonstrating detection of all required reference reflectors before examination begins.

12. Pipe and Tube Ultrasonic Inspection

• Pipe weld inspection per ASTM E213: Standard Practice for Ultrasonic Testing of Metal Pipe and Tubing.

• Circumferential shear wave — used to detect longitudinal flaws in pipe and tube seam welds.

• Axial shear wave — used to detect transverse flaws in pipe and tube.

• Immersion testing — pipe rotating in a water bath with fixed probes for automated 100% coverage.

• Contact pipe testing — manual angle beam scanning adapted for pipe curvature using curved shoe wedges.

• Pipe girth weld inspection per API 1104 — full circumference coverage using multiple probe angles from both sides.

• Curved surface correction — probe shoe curvature must match the pipe OD to maintain consistent beam coupling.

13. UT Procedure Development and Documentation

• Written UT procedure — mandatory per ASME Section V Article 4 before any examination begins.

• Procedure content — scope, material, probe type, frequency, angle, calibration block, reference level, scanning pattern, and acceptance criteria.

• Procedure qualification — demonstrating detection of required reference reflectors before the procedure is approved.

• UT report content — material, probe data, calibration results, indication location and sizing, and accept/reject decision.

• Record retention per ISO 9001:2015 Clause 7.5 — UT reports retained per the applicable code and client requirement.

• Applying RCA to missed or mischaracterized indications — identifying probe selection, calibration, or scan coverage root causes.

Day 5 — HSE Integration, Quality Management, and Case Studies

14. HSE and Quality Management Integration

• Applying HIRARC to UT field operations — working at height, confined space, hot surface contact, and electrical hazards.

• Permit-to-Work for UT on live pressure equipment — mandatory before any contact inspection of pressurized systems.

• Couplant chemical safety — COSHH assessment required for gel couplants used in food-grade or sensitive environments.

• Manual handling — UT scanning of large structures involves repetitive arm movements requiring ergonomic assessment.

• UT in confined spaces — additional atmospheric monitoring and rescue plan required per ISO 45001:2018 Clause 8.1.

• Quality management of UT per ISO 9001:2015 — procedure control, instrument calibration records, and report archive.

• Instrument calibration records — documenting calibration verifications before, during, and after each examination session.

• UT nonconformance per ISO 9001:2015 Clause 10.2 — corrective action required for calibration failure, missed coverage, and invalid examination.

15. Case Studies and Group Discussions

• Case studies from UT failures in Middle East oil and gas, pressure vessel, pipeline, and structural fabrication environments including missed lack of fusion indications from incorrect probe angle selection, thickness measurement errors from uncorrected acoustic velocity mismatch, and pipeline girth weld failures attributed to UT coverage gaps — and the importance of rigorous UT calibration discipline and procedure compliance in preventing in-service failures.

• Group discussion on UT inspection challenges in Middle East environments including manual UT on high-temperature GCC refinery vessels, PAUT adoption for pipeline girth weld inspection on offshore and onshore GCC projects, and applying TOFD for weld quality verification on critical pressure vessels in petrochemical turnarounds.

• Practical flaw sizing workshop — participants interpret A-scan recordings from presented weld inspection scenarios, apply DAC and 6 dB drop sizing methods, determine flaw location and depth, apply the specified acceptance criteria, and complete the UT report.