Study Note 1:Ultrasonic Testing

Source: http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/cc_ut_index.htm

Content:

Section 1: Introduction

1.1: Basic Principles of Ultrasonic Testing1.2: Advantages and Disadvantages1.3: Limitations

Content: Section 2: Physics of Ultrasound

2.1: Wave Propagation2.2: Modes of Sound Wave Propagation2.3: Properties of Acoustic Plane Wave2.4: Wavelength and Defect Detection2.5: Sound Propagation in Elastic Materials2.6: Attenuation of Sound Waves2.7: Acoustic Impedance2.8: Reflection and Transmission Coefficients (Pressure)2.9: Refraction and Snell's Law2.10: Mode Conversion2.11: Signal-to-Noise Ratio2.12: Wave Interaction or Interference2.13: Inverse Square Rule/ Inverse Rule2.14: Resonance2.15 Measurement of Sound2.16 Practice Makes Perfect

Content: Section 3: Equipment & Transducers

3.1: Piezoelectric Transducers3.2: Characteristics of Piezoelectric Transducers3.3: Radiated Fields of Ultrasonic Transducers3.4: Transducer Beam Spread3.5: Transducer Types3.6: Transducer Testing I3.7: Transducer Testing II3.8: Transducer Modeling3.9: Couplants3.10: Electromagnetic Acoustic Transducers (EMATs)

Continues Next Page

3.11: Pulser-Receivers3.12: Tone Burst Generators In Research3.13: Arbitrary Function Generators3.14: Electrical Impedance Matching and Termination3.15: Data Presentation3.16: Error Analysis3.17: Transducer Quality Factor Q3.18: Testing Techniques3.19: UT Equipment Circuitry3.20: Further Reading on Sub-Section 3

Content: Section 4: Calibration Methods

4.1: Calibration Methods4.2: The Calibrations

4.2.1: Distance Amplitude Correction (DAC) 4.2.2: Finding the probe index4.2.3: Checking the probe angle4.2.4: Calibration of shear waves for range V1 Block4.2.5: Dead Zone4.2.7: Transfer Correction4.2.8: Linearity Checks (Time Base/ Equipment Gain/ Vertical Gain)4.2.9: TCG-Time Correction Gain

4.3: Curvature Correction 4.4: Calibration References & Standards4.5: Exercises4.6: Video Time

Content: Section 5: Measurement Techniques

5.1: Normal Beam Inspection5.2: Angle Beams 5.3: Reflector Sizing5.4: Automated Scanning5.5: Precision Velocity Measurements5.6: Attenuation Measurements5.7: Spread Spectrum Ultrasonics5.8: Signal Processing Techniques5.9: Scanning Methods5.10: Scanning Patterns5.11: Pulse Repetition Rate and Penetration5.12: Interferences & Non Relevant Indications5.13: Entry Surface Variables5.14: The Concept of Effective Distance5.15: Exercises

Content: Section 6: Selected Applications & Techniques

6.1: Defects & Discontinuities6.2: Rail Inspection 6.3: Weldments (Welded Joints)6.4: Pipe & Tube6.5: Echo Dynamic6.6: Technique Sheets6.7: Material Properties-Elastic Modulus Measurements6.8: High Temperature Ultrasonic Testing6.9: TOFD Introduction

Content: Section 7: Reference Material

7.1: UT Material Properties7.2: General References & Resources7.3: Video Time

Content: Section 8: Ultrasonic Inspection Quizzes

8.1: Ultrasonic Inspection Quizzes8.2: 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.

Water pathTime / Distance

A

m

p

l

i

t

u

d

e

Display / CRT

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.