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
Guided Wave Ultrasound - Principles and Apllications
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
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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.
15. Used for flaw locating with time-of-flightGroup Velocity in Aluminum
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17. Most displacement is 25% of top and bottom surfaces
18. Bad frequency for defect detection in middleNormalized 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.
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
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
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
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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
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.
