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Guided Wave Ultrasound - Principles and Apllications
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Guided Wave Ultrasound - Principles and Apllications

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This presentation provides a general background on the principles and theory of guided wave ultrasound and its application to inspection of a wide range of structures and materials

This presentation provides a general background on the principles and theory of guided wave ultrasound and its application to inspection of a wide range of structures and materials

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  • 1. Long Range Ultrasound
    Applications of Long Range Ultrasound:
    Benefits, limitations, and technology comparisons.
    Copyright 2009 – WavesinSolids LLC
  • 2. Introduction
    Pseudonyms
    Types of guided waves
    Principles of guided waves in plates
    Principles of guided waves in pipe
    How to generate guided waves
    Applications of guided waves
    Copyright 2009 – WavesinSolids LLC
  • 3. Basic Requirements
    There are a lot of types of guided waves out there but they all have a common denominator:
    A well defined boundary
    Pipeline ID and OD
    At an interface
    Copyright 2009 – WavesinSolids LLC
  • 4. Basic Requirements
    Thickness is comparable to wavelength
    Piezoelectric element
    Thickness
    l
    Zone of constructive/destructive interference
    Copyright 2009 – WavesinSolids LLC
  • 5. Basic Requirements
    What happens when thickness >>> wavelength
    l
    Surface wave
    Thickness
    Bulk wave in volume of material, L-wave or T-wave
    Copyright 2009 – WavesinSolids LLC
  • 6. Basic Requirements
    What is frequency range for ¼” steel
    t ~l ~ ¼ in. (6 mm)
    f (MHz) = v / l
    = 0.24 (in./us) / 0.25 (in.)
    = 1 MHz
    Testing a frequencies above 1 MHz is not recommended for guided waves
    Copyright 2009 – WavesinSolids LLC
  • 7. Pseudonyms
    The name of a guided wave is dependent on the structuretype and how energy is transmitted through the structure.
    Generic Terminology
    Guided waves
    Long range ultrasound
    Boundary Specific
    Surface waves
    Interface waves
    Structure Specific
    Platewaves
    Rod waves
    Cylindrical waves
    Rail waves
    Copyright 2009 – WavesinSolids LLC
  • 8. Pseudonyms
    The name of a guided wave is dependent on the structure type and how energy is transmitted through the structure.
    Plate Waves Names
    Lamb waves
    Axisymmetric waves
    Anti-symmetric waves
    Flexural
    Compressional
    Shear horizontal
    Cylindrical waves
    Longitudinal
    Flexural
    Torsional
    Interface waves
    Love waves
    Scholte waves
    Copyright 2009 – WavesinSolids LLC
  • 9. Unique Characteristics
    Guided wave velocities are dispersive
    Their velocity changes with frequency
    L- and T-wave velocities do not vary with frequency
    Group Velocity in Aluminum
    Modes
    Group velocity
    Frequency
  • 10. Unique Characteristics
    There are two different types of dispersion curves
    Phase Velocity Dispersion Curves
    • Velocity at which a constant wavelength is generated for a given frequency.
    • 11. Used to select incident angle for wedge transducer
    • 12. Used to select element spacing for array transducer.
    • 13. Velocity at guided wave travels in the material.
    • 14. Used to confirm mode experimentally
    • 15. Used for flaw locating with time-of-flight
    Group Velocity in Aluminum
  • 16. Unique Characteristics
    Wave structure can vary through thickness and with frequency
    Understanding Wave Structure
    Normalized in-plane displacement
    Top surface
    Conclusions
    • At this frequency OOP is dominant
    • 17. Most displacement is 25% of top and bottom surfaces
    • 18. Bad frequency for defect detection in middle
    Normalized out-of-plane displacement
    Bottom surface
  • 19. Using the Phase Velocity Curves
    Use Snell’s Law the same way you would for surface wave generation
    Generate L(0,2) mode at 0.2 MHz
    Phase velocity ~ 5.3 mm/us
    Snell’s Law: sin(q1)/v1 = sin(q2)/v2
    q2 = 90 degrees
    q1 = 30 degrees
    L(0,2)
    L(0,1)
  • 20. Using the Phase Velocity Curves
    Use phase velocity to calculate spacing of elements of array transducers
    Generate L(0,2) mode at 0.2 MHz
    Phase velocity ~ 5.3 mm/us
    Wavelength, l = v / f
    Element spacing = l = 26 mm – 1 in.
    L(0,2)
    L(0,1)
  • 21. Guided Waves in Plates
    SH–waves travel via a shearing motion parallel to the surface and perpendicular to wave propagation direction. Shearing motion is not attenuated by water and less attenuated by coatings.
    Lamb waves travel via flexural/compressionalmotion perpendicular and parallel to surface. Flexural motion is significantly attenuated by water, coatings, etc.
  • 22. Guided Waves in Pipe
    Torsional waves (T-modes) travel via a shearing motion parallel to the circumferential direction (q ).Shearing motion is attenuated less by water and less attenuated by coatings.
    Angular vibration
    Radial and axial vibration
    Longitudinal waves (L-modes) travel via flexural/compressionalmotion in the radial and axial directions and may be attenuated significantly by water, coatings, etc.
  • 23. Visualization
    Plate waves
  • 24. Visualization
    Guided waves in pipe
  • 25. Generating Guided Waves
    Piezoelectric Transducers
    Angle beam
    Array
    Electromagnetic acoustic transducers (EMATs)
    Shear horizontal waves in plate
    Lamb wave in plate
    Torsional waves in pipe
    Longitudinal waves in pipe
    Magnetostrictive Transducers
    Torsional waves in pipes
    Shear horizontal waves in plate
  • 26. Generating Guided Waves
    Piezoelectric Transducers
    Advantages
    • Directional control
    • 27. Change angle to get different modes
    • 28. Low-cost
    Advantages
    • Directional control
    • 29. Full OD loading
    • 30. T- and L-modes
    • 31. Premanent installation
    Angle beam
    Piezoceramic Arrays
    Disadvantages
    • Expensive
    • 32. Multiple installation steps
    • 33. Directional control is not 100%
    Disadvantages
    • Difficult to generate Torsional modes
    • 34. Many acoustic interfaces
    • 35. Liquid couplant required
  • Generating Guided Waves
    EMAT Transducers
    Advantages
    • Lamb and SH-wave generation
    • 36. T-wave and L-wave generation
    • 37. No couplant required
    • 38. Possibility for non-contact
    • 39. Bi-directional
    Disadvantages
    • High voltage pulsersreq’d
    • 40. Comparable low SNR
    • 41. Higher cost instrumentation
    • 42. Bi-directional
    • 43. Conductive materials only
  • Generating Guided Waves
    Magnetostrictive Transducers
    Advantages
    • Lamb and SH-wave generation
    • 44. T-wave and L-wave generation
    • 45. Possibility for non-contact
    • 46. Directional control/Bi-directional
    • 47. Permanent installation
    • 48. Alternating magnetic domains transmit ultrasound through material
    Disadvantages
    • Bi-directional
    • 49. Conductive materials only
    • 50. Bonding often required
    • 51. Multi-step sensor installation
    • 52. Ferromagnetic materials only
  • Applications
    Aerospace Applications
    Gas cylinder inspection
    Bridge cable inspection
    Rail flaw detection
    Pipeline inspection
  • 53. Aerospace Applications
    Embed sensors
    Reference Tomogram
    Exposed Surface
    Damage/material loss occurs in-service
    Damage Tomogram
    Filtered Tomogram
  • 54. Aerospace Applications
    Lap-splice inspection
    Bad Bond – Low Amplitude
    Good Bond – High Amplitude
  • 55. Aerospace Applications
    Lap-splice inspection imaging
    Guided wave - Fast 1-D scanning
    Top plate - transmitter
    UT,ET – Slower 2-D scanning
    Bottom plate - receiver
  • 56. Aerospace Applications
    Fatigue crack detection with embedded sensors
    Embed sensors on beams
    SH-60 Helicopter
    2nd generation sensors
    Actual sensors
    Sensors
    Fatigue cracks in transmission beams
  • 57. Gas Cylinder Inspection
    Full body inspection of high-pressure cylinders
    Detects ID and OD surface and internal defects and performs wall thickness measurement.
    Angular position
    Cylinder length
  • 58. Bridge Cable Inspection
    Guided waves are generated focused up and then down the cable.
    Reflections are observed from
  • 59. Bridge Cable Inspection
    Reflections are also observed from cable damage
  • 60. Bridge Cable Inspection
    Benefits and Limitations
    Advantages of LRUT Bridge Cable Inspection
    Corrosion/wire break detection in cable interior and under paint
    Entire cable is inspected from one single sensor location
    Up to 300-feet of cable from one sensor location
    Defect location is possible
    Equipment are lightweight and portable (about 20 lbs total).
    Average cable inspection time is 20 minutes.
    Repeatable data acquisition.
    Limitations of LRUT Bridge Cable Inspection
    LRUT is reflected back from collars, separators, sockets and gatherers. A reflection from a defect underneath the collar, for instance, may be overshadowed by the larger reflection from the collar.
    Defect sizing is limited to minor, moderate, severe
  • 61. Rail Flaw Detection
    Types of defects
    Vertical Split Heads
    Transverse Fissures
    Detail Fractures
    Defective Welds
    Engine Burns
    Horizontal Split Head
  • 62. Rail Flaw Detection
    Guided waves in rail
  • 63. Rail Flaw Detection
    Data Acquisition and Interpretation
    Low speed – inspector interpretation
    High speed – automated interpretation using pattern recognition
  • 64. Pipeline Inspection
    Applications
    Transmission/distribution lines
    Refinery lines
    Offshore risers
    Tank farm lines
    Headers
    Storage sphere support legs
    Refrigeration lines
    Corrosion under insulation (CUI)
    Underground pipelines
  • 65. Pipeline Inspection
    Sensitivity
    Defined in terms of % cross-sectional area reduction
    Original CSA
    % CSA Loss
    • Range
    • 66. Range depends on pipeline, coatings, diameter and product inside the pipeline, and number of elbows.
    Worst case scenario
    Up to 60 feet feet
    Best case scenario
    Up to 1000 feet
  • 67. Guided Waves Applications
    Pipeline Inspection
  • 68. Guided Waves Applications
  • 69. Guided Waves Applications
    DATA FROM 16" GAS TRANSMISSION LINE
  • 70. Guided Waves Applications
    Pipeline Inspection
  • 71. Summary
    Guided wave inspection can be a powerful too
    Good match for screening applications
    Good match for remote inspections
    Selecting the right mode and sensor for the inspection applications
    Convey the effects that surface roughness, coatings, underground versus aboveground, elbows, etc. have on inspection range and sensitivity to the client to manage expectations.