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My ASNT Level III UT Testing-Self Study Notes 2

My ASNT Level III UT Testing-Self Study Notes 2

charliechong
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My ASNT Level III UT Testing-Self Study Notes 2

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  1. Preparatory Notes for My ASNT NDT Level III Examination - Ultrasonic Testing, UT Reading Two- Part 1 My pre-exam self study note - 2014 Charlie Chong/ Fion Zhang

  2. Charlie Chong/ Fion Zhang

  3. Critical Reading

  4. Charlie Chong/ Fion Zhang

  5. http://en.wikipedia.org/wiki/Greek_alphabet

  6. Numerical Prefix  Micro - (µ) a prefix in the SI and other systems of units denoting a factor of 10-6(one millionth)  Nano - a prefix in the SI and other systems of units denoting a factor of 10-9 (one billionth)  Pico - a prefix in the International System of Units (SI) denoting a factor of 10-12

  7. Fion Zhang 2014/September/5 http://meilishouxihu.blog.163.com/

  8. Contents Chapter 1 - Physical Principles 1. Wave Characteristics 2. Reflection 3. Refraction 4. Mode Conversion 5. Critical Angles 6. Diffraction 7. Resonance 8. Attenuation 9. Chapter 1 Review Questions Charlie Chong/ Fion Zhang

  9. Chapter 2 – Equipment 1. Basic Instrumentation 2. Transducers and Coupling 3. Special Equipment Features 4. Chapter 2 Review Questions Charlie Chong/ Fion Zhang

  10. Chapter 3 - Common Practices 1. Approaches to Testing 2. Measuring System Performance 3. Reference Reflectors 4. Calibration 5. Chapter 3 Review Questions Charlie Chong/ Fion Zhang

  11. Chapter 4 - Practical Considerations 1. Signal Interpretation 2. Causes of Variability 3. Special Issues 4. Weld Inspection 5. Immersion Testing 6. Production Testing 7. In-service Inspection 8. Chapter 4 Review Questions Charlie Chong/ Fion Zhang

  12. Chapter 5 - Codes and Standards 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Excerpts Taken from a Representative Building Code 11. Chapter 5 Review Questions Typical Approaches Summaries of Requirements ASTM Excerpts Taken from ASTM A609 ASME Excerpts Taken from ASME Boiler and Pressure Vessel Code Military Standards Excerpts Taken from MIL-STD-2154 Building Codes Charlie Chong/ Fion Zhang

  13. Chapter 6 - Special Topics 1. Resonance Testing 2. Flaw Sizing Techniques Charlie Chong/ Fion Zhang

  14. Appendix A - A Representative Procedure for Ultrasonic Weld Inspection Form A. Ultrasonic Testing Technique Sheet Form B. Ultrasonic Inspection Results Form Review Questions for a Representative Procedure for Ultrasonic Appendix B - List of Materials, Velocities, and Impedances Appendix C - Answer Key to Chapter Review Questions 113 Appendix D - References Charlie Chong/ Fion Zhang

  15. Chapter 1 Physical Principles

  16. Contents Chapter 1 - Physical Principles 1. Wave Characteristics 2. Reflection 3. Refraction 4. Mode Conversion 5. Critical Angles 6. Diffraction 7. Resonance 8. Attenuation 9. Chapter 1 Review Questions

  17. 1.0 Sound is the propagation of mechanical energy (vibrations) through solids, liquids and gases. The ease with which the sound travels, however, is dependent upon the detailed nature of the material and the pitch (frequency) of the sound. At ultrasonic frequencies 20KHz (above 20,000 Hertz [Hz]), sound propagates well through most elastic or near-elastic solids and liquids, particularly those with low viscosities. At frequencies above 100 kilohertz (100KHz or 0.1MHz), sound energy can be formed into beams, similar to that of light, and thus can be scanned throughout a material, not unlike that of a flashlight used in a darkened room. Such sound beams follow many of the physical rules of optics and thus can be reflected, refracted, diffracted and absorbed (when non-elastic materials are involved). At extremely high frequencies (above 100 megahertz [MHz]), the sound waves are severely attenuated and propagation is limited to short travel distances. General: The common wave modes and their characteristics are summarized in Table 1.1.

  18. 1.1 The propagation of ultrasonic waves depends on the mechanical characteristics of density and elasticity, the degree to which the material supporting the waves is homogeneous and isotropic, and the diffraction phenomena found with continuous (or quasi-continuous) waves. Continuous waves are described by their wavelength, i.e., the distance the wave advances in each repeated cycle. This wavelength is proportional to the velocity at which the wave is advancing and is inversely proportional to its frequency of oscillation. Wavelength may be thought of as the distance from one point to the next identical point along the repetitive waveform. Wavelength is described mathematically by Equation 1-1. Wave Characteristics: Equation 1-1

  19. The velocity at which bulk waves travel is determined by the material's elastic moduli and density. The expressions for longitudinal and transverse waves are given in Equations 1-2 and 1-3, respectively. Equations 1-2 Equations 1-3 Where: VLis the longitudinal bulk wave velocity, VTis the transverse (shear) wave velocity, G is the shear modulus, E is Young's modulus of elasticity, μ is the Poisson ratio, and p is the material density.

  20. Typical values of bulk wave velocities in common materials are given in Table 1.2. Table 1.2: Acoustic Velocities, Densities and Acoustic Impedances of Common Materials Material VL(m/s) VT(m/s) Z ρ (g/cm3) Steel 5900 3230 45.0 7.63 Aluminum 6320 3130 17.0 2.70 Plexiglass 2730 1430 3.2 1.17 - Water 1483 1.5 1.00 Quartz 5800 2200 15.2 2.62

  21. Table 1.2 it is seen that, in steel, a longitudinal wave travels at 5.9 km/s, while a shear wave travels at 3.2 km/s. In aluminum, the longitudinal wave velocity is 6.3 km/s while the shear velocity is 3.1 km/s. The wavelengths of sound for each of these materials are calculated using Equation 1-1 for each applicable test frequency used. For example, a 5 MHz L-wave in water has a wavelength equal to 1483/ (5 x10-6) m or 0.298 mm. Quiz: Calculate the wavelength for  L-wave Steel at 3 MHz  S-wave Aluminum at 3 MHz

  22. When sound waves are confined within boundaries, such as along a free surface or between the surfaces of sheet materials, the waves take on a very different behavior, being controlled by the confining boundary conditions. These types of waves are called guided waves, i.e., they are guided along the respective surfaces, and exhibit velocities that are dependent upon elastic moduli, density, thickness, surface conditions, and relative wavelength interactions with the surfaces.  For Rayleigh waves, the useful depth of penetration is restricted to about one wavelength below the surface. The wave motion is that of a retrograde ellipse.  For Wave modes such as those found with Lamb waves have a velocity of propagation dependent upon the operating frequency, sample thickness and elastic moduli. They are dispersive (velocity changes with frequency) in that pulses transmitted in these modes tend to become stretched or dispersed as they propagate in these modes and/or materials which exhibit frequency-dependent velocities.

  23. 1.2 Ultrasonic waves, when they encounter a discrete change in materials, as at the boundary of two dissimilar materials, are usually partially reflected. If the incident waves are perpendicular to the material interface, the reflected waves are redirected back toward the source from which they came. The degree to which the sound energy is reflected is dependent upon the difference in acoustic properties, i.e., acoustic impedances, between the adjacent materials. Reflection: Acoustic impedance (Equation 1-4) is the product of a wave's velocity of propagation and the density of the material through which the wave is passing. Z = ρ ρ x V Equation 1-4 Where: Z is the acoustic impedance, ρis the density, and V is the applicable wave velocity.

  24. Table 1.2 lists the acoustic impedances of several common materials. The degree to which a perpendicular wave is reflected from an acoustic interface is given by the energy reflection coefficient. The ratio of the reflected acoustic energy to that which is incident upon the interface is given by Equation 1-5. R = (Z2-Z1)2 (Z2 + Z1)2 Equation 1-5

  25. Where: R is the Coefficient of Energy Reflection for normal incidence Z is the respective material acoustic impedances With: Z1= incident wave material, Z2= transmitted wave material, and T is the Coefficient of Energy Transmission. Note: T + R= 1 (unity)

  26. In the case of water-to-steel, approximately 88 percent of the incident longitudinal wave energy is reflected back, into the water, leaving 12 percent to be transmitted into the steel. These percentages are arrived at using Equation 1-5 with Zsteel= 45 and Zwater=1.5. Thus: R =(45 - 1.5)2/ (45 + 1.5)2= (43.S/46.5)2= 0.875, or 88 percent and T = 1 - R = 1 - 0.88 = 0.12, or 12 percent. Quiz: Calculate the reflection Coefficient of Aluminum to Water Interface, using data from table 1.3

  27. Note: When Equation 1-5 is expressed for pressure waves rather than the energy contained in the waves, the terms in parentheses are not squared. Energy Domain: R = (Z2-Z1)2 (Z2 + Z1)2 Pressure Domain: R = (Z2-Z1) (Z2 + Z1) Charlie Chong/ Fion Zhang

  28. 1.3 When a sound wave encounters an interface at an angle other than perpendicular (oblique incidence), reflections occur at angles equal to the incident angle (as measured from the normal or perpendicular axis). If the sound energy is partially transmitted beyond the interface, the transmitted wave may be (1) refracted (bent), depending on the relative acoustic velocities of the respective media, and/or (2) partially converted to a mode of propagation different from that of the incident wave. Figure 1.1a shows normal reflection and partial transmission, while Figure 1.1b shows oblique reflection and the partition of waves into reflected and transmitted wave modes. Refraction:

  29. Figure 1.1. Incident, reflected, transmitted, and refracted waves at a liquid- solid interface

  30. Referring to Figure 1.1b, Snell's Law may be stated as: (Eq. 1-6) For example, at a water-plexiglass interface, the refracted shear wave angle is related to the incident angle by: sin (β = (1430/1483) • sin α = (0.964)•sin α For an incident angle of 30 degrees, sin β = 0.964 x 0.5 and β = 28.8 degrees

  31. 1.4 It should be noted that the acoustic velocities (V1 and V2) used in Equation 1- 6 must conform to the modes of wave propagation which exist for each given, case. For example, a wave in water (which supports only longitudinal waves) incident on a steel plate at an angle other than 90 degrees can generate longitudinal, shear, as well as heavily damped surface or other wave modes, depending on the incident angle and test part geometry. The wave may be totally reflected if the incident angle is sufficiently large. In any case, the waves generated in the steel will be refracted in accordance with Snell's Law, whether they are longitudinal or shear waves. Mode Conversion:

  32. Figure 1.2 shows the distribution of transmitted wave energies as a function of incident angle for a water-aluminum interface. For example, an L-wave with an incidence angle of 8 degrees in water results in (1) a transmitted shear wave in the aluminum with 5 percent of the incident beam energy, (2) a transmitted L-wave with 25 percent and (3) a reflected L-wave with 70 percent of the incident beam energy. It is evident from the figure that for low incidence angles (less than the first critical angle of 14 degrees), more than one mode may be generated in the aluminum. Note that the sum of the reflected longitudinal wave energy and the transmitted energy or energies is equal to unity at all angles. The relative energy amplitudes partitioned into the different modes are dependent upon several variables, including each material's acoustic impedance, each wave mode velocity (in both the incident and refracted materials), the incident angle, and the transmitted wave mode(s) refracted angle(s).

  33. 11111

  34. 11111 Reflected Longitudinal mode Shear mode

  35. 11111 70% 25% 5%

  36. 11111 Reflected wave energy Fist critical angle Second critical angle

  37. 1.5 The critical angle for the interface of two media with dissimilar acoustic wave velocities is the incident angle at which the refracted angle equals 90 degrees (in accordance with Snell's law) and can only occur if the wave mode velocity in the second medium is greater than the wave velocity in the incident medium. It may also be defined as the incident angle beyond which a specific mode cannot occur in the second medium. Critical Angles: In the case of a water-to-steel interface, there are two critical angles derived from Snell's law. The first occurs at an incident angle of 14.5 degrees for the longitudinal wave. The second occurs at 27.5 degrees for the shear wave. Equation 1-7 can be used to calculate the critical incident angle for any material combination. Eq. 1-7

  38. 11111 Reflected wave energy Fist critical angle, 14.5 ° Second critical angle, 27.5°

  39. For example, the first critical angle for a water-aluminum interface is calculated using the critical angle equation as: α1st Critical= sin-1(1483/6320) = 13.6 °

  40. 1.6 Plane waves advancing through homogeneous and isotropic elastic media tend to travel in straight ray paths unless a change in media properties is encountered. A flat (much wider than the incident beam) interface of differing acoustic properties redirects the incident plane wave in the form of a specularly (mirror like) reflected or refracted plane wave as discussed above. The assumption in this case is that the interface is large in comparison to the incident beam's dimensions and thus does not encounter any "edges.“ Diffraction:

  41. Beam Incidences at edge

  42. On the other hand, when a wave encounters a point reflector (small in comparison to a wavelength), the reflected wave is reradiated as a spherical wave front. Thus, when a plane wave encounters the edges of reflective interfaces, such as near the tip of a fatigue crack, specular reflections occur along the "flat" surfaces of the crack and cylindrical wavelets are launched from the edges. Since the waves are coherent, i.e., the same frequency (wavelength) and in phase, their redirection into the path of subsequent advancing plane waves results in incident and reflected (scattered) waves interfering, i.e., forming regions of reinforcement (constructive interference) and cancellation (destructive interference).

  43. Wave Diffraction Charlie Chong/ Fion Zhang

  44. Wave Diffraction Small Reflector 2 Narrow Edges / Slit

  45. Wave Diffraction Edges Reflector 2 Narrow Edges / Slit

  46. Wave Diffraction http://hannibalphysics.wikispaces.com/file/view/wave-diffraction-2.gif/314851388/wave-diffraction-2.gif

  47. Wave Diffraction

  48. Wave Diffraction - with interference

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