USFD in Rails & Welds

1. USFD inRails & Welds

2. DEVELOPMENT OF FLAWS IN RAILS Development of flaws in rails is inevitable Two main reasons are the inherent defects and fatigue of rails due to passage of traffic Rail stresses are increasing day by day due to which mechanical properties of rail steel are being exceeded with passage of wheels

3. Defects in Rails SURFACE DEFECTS INTERNAL DEFECTS

4. VARIOUS PLANES FOR DEFECT LOCATION LONGITUDINAL PLANE HORIZONTAL PLANE TRANSVERSE PLANE

5. CRACK IN HEAD CRACK IN HEAD WEB JUNCTION CRACK IN WEB

6. Transverse defect

7. Gauge face corner defect

8. Non Gauge Face side defect

9. Longitudinal Vertical defect

10. Star Crack or Bolt Hole Crack

11. PROBES

12. Probes Used for Ultrasonic Testing • 00 or NORMAL Probe (4 MHZ) • 700 Forward Probe (2 MHz) • 700 Backward Probe (2 MHz) • 700 Shifted/Forward Probe (2 MHz) • 700 Shifted/Backward Probe (2 MHz) • 450 Probe (2 MHz) • 450 Tandem Test Rig (2 MHz) • 700 Miniature Probe (2 MHz) • 00 Probe (2 MHZ)

13. BASIC PRINCIPLES of USFD TESTING

15. SONIC & SOUND • Sonic is related to or using sound. • Sound waves are categorized by their frequencies as..... • Subsonic ( less than 20 Hz) • SONIC ( BETWEEN 20 & 20,000 Hz) • Ultrasonic ( > 20,000 Hz) • Sound Waves are Mechanical Waves • Other Waves are Electro Magnetic Waves

16. CLASSIFICATION OF SOUND WAVES • LONGITUDINAL OR COMPRESSION WAVES • TRANSVERSE OR SHEAR WAVES • SURFACE WAVES

17. LONGITUDINAL WAVES • Vibration of the particles of the material are in the same direction as that of propagation of the wave • Sound energy is transmitted from one particle to another by alternating compression & hence these are also called compression waves. • These can travel through solids , liquid & gases. • These are the fastest of all wave types.

19. TRANSVERSE WAVES • Vibration of the particles of the material are in a direction perpendicular to the direction of propagation of the wave • Energy is transmitted from one particle to another by shear. Hence also known as shear waves. • These can travel only through solids and on surface of liquids. These can not travel through liquids and gases as they do not have any shear strength. • Their velocity in any given media is approx. half the velocity of longitudinal Waves.

21. SURFACE WAVES • These are confined to a very thin layer of material surface and are therefore not important from the point of view of rail flaw detection

22. WAVE VELOCITIES

23. WAVE PROPAGATION • Velocity of travel v depends upon the material through which the wave is to propagate V = f *  • HIGHER THE FREQUENCY, LOWER WILL BE THE WAVELENGTH

24. WAVE PROPAGATION • Reflection • Refraction • Transformation • Acoustic Impedance • Attenuation

25. TRASFORMATION OF WAVES i=r REFLECTED WAVE INCIDENT WAVE i r PERSPEX, v1 MEDIUM - I STEEL, v2 MEDIUM - II  REFRACTED WAVE

26. Mode Conversion • When a longitudinal wave hits an interface at an angle, some of the energy can cause particle movement in the transverse direction to start a shear (transverse) wave. • Mode conversion, occurs when a wave encounters an interface between material of different accoustic impedance and the incident angle is not normal to interface.

27. TRASFORMATION OF WAVES REFLECTED WAVES INCIDENT WAVE T L L rL i rT PERSPEX, v1 MEDIUM - I STEEL, v2 MEDIUM - II T vL1=2730 m/s vT1=1430 m/s vL2=5900 m/s vT2=3230 m/s L L T REFRACTED WAVE

28. TRASFORMATION OF WAVES L L rL i MEDIUM - I MEDIUM - II vL1=2730 m/s vT1=1430 m/s vL2=5900 m/s vT2=3230 m/s

29. TRASFORMATION OF WAVES T L i rT MEDIUM - I MEDIUM - II vL1=2730 m/s vT1=1430 m/s vL2=5900 m/s vT2=3230 m/s

30. TRASFORMATION OF WAVES L i MEDIUM - I MEDIUM - II L L vL1=2730 m/s vT1=1430 m/s vL2=5900 m/s vT2=3230 m/s

31. TRASFORMATION OF WAVES L i MEDIUM - I MEDIUM - II T T vL1=2730 m/s vT1=1430 m/s vL2=5900 m/s vT2=3230 m/s

32. TRASFORMATION OF WAVES INCIDENT WAVE L TOTAL INTERNAL REFLECTION ic1 L PERSPEX, v1 MEDIUM - I L STEEL, v2 MEDIUM - II T ic1=27.70 L=900 T=33.30 T

33. TRASFORMATION OF WAVES INCIDENT WAVE L TOTAL INTERNAL REFLECTION ic2 T L PERSPEX, v1 MEDIUM - I L STEEL, v2 MEDIUM - II T ic2=57.70 L=900 T=900

34. Total internal reflection • FIRST CRITICAL ANGLE - 27.70 • SECOND CRITICAL ANGLE - 57.7O • This phenomenon is used for testing by Angular Probes

35. USABLE RANGE FOR ANGLE BEAM PROBES

36. ACOUSTIC IMPEDANCE • It is a property of the material which determines its affinity for propagation of sound waves. • The acoustic impedance (Z) of a material is defined as the product of density (p) and acoustic velocity (V) of that material. • Z=pV

37. ACOUSTIC IMPEDANCE

38. Reflection and Transmission Coefficients • Ultrasonic waves are reflected at boundaries where there is a difference in acoustic impedance (Z) . • Fractional amount of transmitted sound energy plus the fractional amount of reflected sound energy equals one. • The greater the impedance mismatch, the greater the percentage of energy that will be reflected.

39. Reflection and Transmission Coefficients • R is reflection coefficient. Multiplying the reflection coefficient by 100, yields the amount of energy reflected as a percentage of the original energy. • Since the amount of reflected energy plus the transmitted energy must equal the total amount of incident energy, the transmission coefficient is calculated by simply subtracting the reflection coefficient from one.

40. REFLECTION AT INTERFACES

41. 12% Transducer 1.44% 88% 100% WATER WATER 12% 10.56% STEEL AIR

42. COUPLANT

43. ATTENUATION • When sound travel through a medium, its intensity diminishes with distance. • The combined effect of scattering and absorption is called Attenuation. • Absorption .. is energy consumed in the process of causing vibrations of the particles of matter. • Scattering.. is energy lost by dispersion of waves all over in the material. • Ultrasonic attenuation is, therefore, the rate of decay of the wave as it propagate through material.

44. ATTENUATION • ATTENUATION= D3 f4 / V4 i.e.. A = D3 /  Where D = avg. Grain size of the material • Thus loss of energy is more for • Coarse material .. welds • Smaller wavelengths (or higher frequencies) in a given material & for shear waves as compared to long. Waves of same frequency in same material.

45. WAVE LENGTH & DETECTABLE FLAW SIZE IN STEEL Detectable size of flaw=wavelength/2

46. FLAW DETECTION

47. FLAW DETECTION • An ultrasonic wave is first introduced into the rail steel • The ultrasonic wave will travel through the rail until it comes across a boundary with a dissimilar medium . • At the boundary the wave will either get reflected or refracted depending upon the acoustic impedance of the two media.

48. FLAW DETECTION (contd) • The boundary could be the other surface of the rail or an internal flaw. • A flaw in rail is air void /crack or any other material (slag) having acoustic impedance much different from that of steel. • The reflected US wave can be detected and the location & size of the source of reflection can be interpreted.

49. FLAW DETECTION (contd) • This is called “pulse echo” or reflection technique. • Due to the shape & fixity of rail, the transmission & reception of signals has to be done from the same side ( rail head) • The other but less commonly used method is called “transmission technique”

50. FLAW DETECTION (contd) • A plane (two-dimensional) discontinuity (e.g. material separation, crack) OR a volumetric discontinuity (hollow space, foreign material) reflects the ultrasonic waves mostly in a certain direction. • If the reflected portion of the sound wave is not received by the probe then it is unlikely that the discontinuity will be detected. The possibilities of detection only increase when the plane discontinuity is hit normally by the sound beam.