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

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Guided Wave Ultrasound - Principles and Apllications

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