Ut testing section 1 ultrasonic testing

Study Note 1: Ultrasonic Testing

Source: http://www.ndted.org/EducationResources/CommunityCollege/Ultra sonics/cc_ut_index.htm

Content: Section 1: Introduction 1.1: Basic Principles of Ultrasonic Testing 1.2: Advantages and Disadvantages 1.3: Limitations

Content: Section 2: Physics of Ultrasound 2.1: Wave Propagation 2.2: Modes of Sound Wave Propagation 2.3: Properties of Acoustic Plane Wave 2.4: Wavelength and Defect Detection 2.5: Sound Propagation in Elastic Materials 2.6: Attenuation of Sound Waves 2.7: Acoustic Impedance 2.8: Reflection and Transmission Coefficients (Pressure) 2.9: Refraction and Snell's Law 2.10: Mode Conversion 2.11: Signal-to-Noise Ratio 2.12: Wave Interaction or Interference 2.13: Inverse Square Rule/ Inverse Rule 2.14: Resonance 2.15 Measurement of Sound 2.16 Practice Makes Perfect

Content: Section 3: Equipment & Transducers 3.1: Piezoelectric Transducers 3.2: Characteristics of Piezoelectric Transducers 3.3: Radiated Fields of Ultrasonic Transducers 3.4: Transducer Beam Spread 3.5: Transducer Types 3.6: Transducer Testing I 3.7: Transducer Testing II 3.8: Transducer Modeling 3.9: Couplants 3.10: Electromagnetic Acoustic Transducers (EMATs) Continues Next Page

3.11: Pulser-Receivers 3.12: Tone Burst Generators In Research 3.13: Arbitrary Function Generators 3.14: Electrical Impedance Matching and Termination 3.15: Data Presentation 3.16: Error Analysis 3.17: Transducer Quality Factor “Q” 3.18: Testing Techniques 3.19: UT Equipment Circuitry 3.20: Further Reading on Sub-Section 3

Content: Section 4: Calibration Methods 4.1: Calibration Methods 4.2: The Calibrations 4.2.1: Distance Amplitude Correction (DAC) 4.2.2: Finding the probe index 4.2.3: Checking the probe angle 4.2.4: Calibration of shear waves for range V1 Block 4.2.5: Dead Zone 4.2.7: Transfer Correction 4.2.8: Linearity Checks (Time Base/ Equipment Gain/ Vertical Gain) 4.2.9: TCG-Time Correction Gain 4.3: Curvature Correction 4.4: Calibration References & Standards 4.5: Exercises 4.6: Video Time

Content: Section 5: Measurement Techniques 5.1: Normal Beam Inspection 5.2: Angle Beams 5.3: Reflector Sizing 5.4: Automated Scanning 5.5: Precision Velocity Measurements 5.6: Attenuation Measurements 5.7: Spread Spectrum Ultrasonics 5.8: Signal Processing Techniques 5.9: Scanning Methods 5.10: Scanning Patterns 5.11: Pulse Repetition Rate and Penetration 5.12: Interferences & Non Relevant Indications 5.13: Entry Surface Variables 5.14: The Concept of Effective Distance 5.15: Exercises

Content: Section 6: Selected Applications & Techniques 6.1: Defects & Discontinuities 6.2: Rail Inspection 6.3: Weldments (Welded Joints) 6.4: Pipe & Tube 6.5: Echo Dynamic 6.6: Technique Sheets 6.7: Material Properties-Elastic Modulus Measurements 6.8: High Temperature Ultrasonic Testing 6.9: TOFD Introduction

Content: Section 7: Reference Material 7.1: UT Material Properties 7.2: General References & Resources 7.3: Video Time Content: Section 8: Ultrasonic Inspection Quizzes 8.1: Ultrasonic Inspection Quizzes 8.2: Online UT Quizzes

Section 1: Introduction

1.1:

Basic Principles of Ultrasonic Testing

ULTRASONIC INSPECTION is a nondestructive method in which beams of high-frequency sound waves are introduced into materials for the detection of surface and subsurface flaws in the material. The sound waves travel through the material with some attendant loss of energy (attenuation) and are reflected at interfaces. The reflected beam is displayed and then analyzed to define the presence and location of flaws or discontinuities. The degree of reflection depends largely on the physical state of the materials forming the interface and to a lesser extent on the specific physical properties of the material.

For example, sound waves are almost completely reflected at metal/gas interfaces. Partial reflection occurs at metal/liquid or metal/solid interfaces, with the specific percentage of reflected energy depending mainly on the ratios of certain properties of the material on opposing sides of the interface.

Cracks, laminations, shrinkage cavities, bursts, flakes, pores, disbonds, and other discontinuities that produce reflective interfaces can be easily detected.

Inclusions and other in-homogeneities can also be detected by causing partial reflection or scattering of the ultrasonic waves or by producing some other detectable effect on the ultrasonic waves.

In ultrasonic testing, the reflected wave signal is transformed into an electrical signal by the transducer and is displayed on a screen. In the applet below, the reflected signal strength is displayed versus the time from signal generation to when a echo was received. Signal travel time can be directly related to the distance that the signal traveled. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained.

http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Graphics/Flash/ultrasoundInspection.swf

Basics of Ultrasonic Test- Contact Pulse Echo Method

http://www.cnde.iastate.edu/faa-casr/engineers/Supporting%20Info/Supporting%20Info%20Pages/Ultrasonic%20Pages/Ultra-principles.html

Immersion Method- Figure below shows an immersion UT setup with CRT or computer screen display. IP indicates the initial pulse while FW and BW indicate the front and back wall of the specimen, respectively.

Amplitude

Display / CRT

Water path

Time / Distance

Basics of Ultrasonic Test- A-Scan

1.2: Source-1: The advantages of ultrasonic testing include Ultrasonic Inspection is a very useful and versatile NDT method. Some of the advantages of ultrasonic inspection that are often cited include:  It is sensitive to both surface and subsurface discontinuities.  The depth of penetration for flaw detection or measurement is superior to other NDT methods.  Only single-sided access is needed when the pulse-echo technique is used.  It is highly accurate in determining reflector position and estimating size and shape.  Minimal part preparation is required.  Electronic equipment provides instantaneous results.  Detailed images can be produced with automated systems.  It has other uses, such as thickness measurement, in addition to flaw detection.

Source-2: The advantages of ultrasonic testing include     

It can be used to determine mechanical properties and microstructure.

It can be used for imaging and microscopy.

It is portable and cost effective.

It can be used with all states of matter except plasma and vacuum.

It is not affected by optical density.

Source-3: Advantages and Disadvantages The principal advantages of ultrasonic inspection as compared to other methods for nondestructive inspection of metal parts are:  Superior penetrating power, which allows the detection of flaws deep in the part. Ultrasonic inspection is done routinely to thicknesses of a few meters on many types of parts and to thicknesses of about 6 m (20 ft) in the axial inspection of parts such as long steel shafts or rotor forgings  High sensitivity, permitting the detection of extremely small flaws  Greater accuracy than other nondestructive methods in determining the position of internal flaws, estimating their size, and characterizing their orientation, shape, and nature  Only one surface needs to be accessible

 Operation is electronic, which provides almost instantaneous indications of flaws. This makes the method suitable for immediate interpretation, automation, rapid scanning, in-line production monitoring, and process control. With most systems, a permanent record of inspection results can be made for future reference  Volumetric scanning ability, enabling the inspection of a volume of metal extending from front surface to back surface of a part  Nonhazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity  Portability  Provides an output that can be processed digitally by a computer to characterize defects and to determine material properties

The disadvantages of ultrasonic inspection include the following:  Manual operation requires careful attention by experienced technicians.  Extensive technical knowledge is required for the development of inspection procedures.  Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.  Discontinuities that are present in a shallow layer immediately beneath the surface may not be detectable.  Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts being inspected.  Reference standards are needed, both for calibrating the equipment and for characterizing flaws.

1.3:

Limitations (Disadvantages)

As with all NDT methods, ultrasonic inspection also has its limitations, which include: • Surface must be accessible to transmit ultrasound.

• Skill and training is more extensive than with some other methods.

• It normally requires a coupling medium to promote the transfer of sound energy into the test specimen.

• Materials that are rough, irregular in shape, very small, exceptionally thin or not homogeneous are difficult to inspect.

• Cast iron and other coarse grained materials are difficult to inspect due to low sound transmission and high signal noise.

• Linear defects oriented parallel to the sound beam may go undetected.

• Reference standards are required for both equipment calibration and the characterization of flaws.