UNIT 3 NON DESTRUCTIVE TESTING.pdf
- 3. What is NDT? • Non-destructive testing (NDT) is a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage. • The terms non-destructive examination (NDE), non-destructive inspection (NDI), and non-destructive evaluation (NDE) are also commonly used to describe this technology.
- 4. • Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research.
- 5. • NDT does not directly measure mechanical properties but they are used to locate defects or flaws in the component. • Flaws reduce useful life of component resulting in premature failure even with a sound design and proper selection of materials. • To obtain high level of reliability , defect should be absent or at minimum level. • NDT is carried out periodically. • Replacement of component before its premature failure to avoid dangerous results.
- 6. Applications of NDT • NDT is commonly used in forensic engineering, mechanical engineering, petroleum engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine, and art. • Innovations in the field of non-destructive testing have had a profound impact on medical imaging, including on echocardiography, medical ultrasonography, and digital radiography.
- 7. DIFFERENT NDT METHODS • VISUAL INSPECTION • LIQUID/DYE PENETRATION TEST • MAGNETIC PARTICLE TEST • THERMOGRAPHY TEST • RADIOGRAPHY TEST • EDDY CURRENT TEST • ULTRASONIC TEST • ACOUSTIC EMISSION TEST
- 8. VISUAL INSPECTION Visual Inspection is one of the most widely used Non-Destructive Testing methods for the detection of discontinuities before they cause major problems, e.g. poor welding, surface defects, corrosion pits, general condition, degradation, blockages and foreign materials.
- 9. Generally, almost any specimen can be visually examined to determine the accuracy of its fabrication. • For example, visual inspection can be used to determine whether the part was fabricated to the correct size, whether the part is complete, or whether all of the parts have been appropriately incorporated into the device.
- 10. Types of Visual Inspection 1. Unaided Visual Inspection 2.Aided Visual Inspection
- 11. Unaided Visual Inspection • It is also Known as Direct Visual Inspection • It can be accomplished with the help of naked eye • It can done with out the help of optical aids • Defects can be detected are – Absence of cracks, Corrosion layer, surface porosity, Misalignment of parts
- 12. Aided Visual Inspection • It is also known as Indirect Visual Inspection • It is performed using optical instruments • This will identify the defects which cannot detect with human eye • It permits visibility to areas are not accessible to human eye
- 13. Tools Used in Visual Inspection • Mirrors • Magnifying Glasses • Microscopes • Borescope • Endoscope
- 14. Magnifying Mirrors • It is also known as concave spherical mirrors • It is used to magnify the areas which are not accessible to human eye.
- 15. Magnifying Glass • It is also called as Hand Lens • This lens is used to produce a magnified Image • Magnification depends upon the position where it is being placed between the human eye and the object • For higher power magnification, double or multiple lenses are used
- 16. Microscope Microscope is used to magnify the image of a small object Borescope • Which is used to inspect the inside of a narrow tube • It is a flexible tube with an eyepiece at one end and objective lens at another end • Light is passed through the lens and to obtain a clear image
- 17. Endoscope • It is bit superior than borescope • Magnification factor of 10X is obtained • Available up to smaller dia. of 1.7 mm and length up to 100-150mm
- 18. Applications of Visual Inspection • It is used to inspect whether there is a misalignment of parts in the equipment • It checks for corrosion, erosion, cracks and deformities of machine components • It inspect the plant components for any leakage or abnormal operation • It is used to identify the defects in weld ments
- 19. Limitations of Visual Inspections • Can identify only large discontinuities • Limited to surface discontinuities • Skilled labour required • Result depend on the eye resolution of the inspector • It may cause eye fatigue to the inspector
- 20. Material factors that affect Visual Testing • Surface Condition – Cleanliness – Colour – Texture • Physical Conditions – Specimen Condition – Shape and Size – Temperature • Environmental Factors – Atmosphere – Cleanliness – Humidity and Temperature – Safety • Physiological Factors – Physical Comfort – Health , mental attitude
- 21. Dye Penetrant Inspection • Invisible cracks, porosity and other defects on the surface of components easily detected by this technique. • Components may be ferrous, nonferrous, plastic, glass or ceramic. Procedure 1. Cleaning of surface. 2. Drying of surface.
- 22. 3.Applying dye-penetrant on clean and dry surface. It is allowed to penetrate in surface flaws. i) Liquid Soluble Penetrant ii) Fluroscent 4.Removing excess penetrant by soft or clean cotton. 5.Applying developer on surface. This pulls out dye from flaws and flaws are revealed by colour of dye. Instead of developer, fine developing powder or talc powder can be sprinkled on the surface.
- 24. Advantages of Dye Penetrant Inspection • This test can be applied to almost any type of metals, non-metals, magnetic or non magnetic type. • Simple to utilize and control. • Results of test can be interpreted fastly. • Cost of test is very less as it does not require any instrument or electronic display units.
- 25. Disadvantages of Dye Penetrant Inspection • Cleaning of components is must before and after testing to avoid rusting • Misleading results may be obtained in case of components with surface films and coatings • Only surface defects can be detected • Test is not applicable for powder metallurgical components
- 26. Magnetic Particle (Magnaflux) Inspection • It is used to detect various kinds of flaws in ferromagnetic components such as weldings, castings, forgings of iron and steel. • Component to be inspected for flaws is magnetized. • In dry method of inspection special fine ferromagnetic powder is applied on surface .
- 27. • This test is a very fast method of inspection and often used to test aerospace components and automobile parts. • This test is generally used to detect internal cracks like shrinkage cavities, hot tears, zones of corrosion and non-metallic inclusions
- 28. Magna flux Test Procedure:- • Cleaning Surface • Magnetization • Application of ferromagnetic Powder • Observation and Inspection • Demagnetization
- 30. Advantages of Magnaflux Test • Sub-surface cracks can be easily detected • Almost any shaped and sized component can be tested for defects • Instruments are portable and easy to handle • Highly sensitive method to detect small and shallow surface cracks
- 31. Disadvantages of Magnaflux Test • Method is applicable only to ferromagnetic materials • Surface plating or thin paint coating affect the sensitivity of the test • After testing, demagnetization is a must • Local heating and sparking is possible during test hence proper care must be taken
- 32. Thermography test Infrared thermography is equipment or method, which detects infrared energy emitted from object, converts it to temperature, and displays image of temperature distribution. The image of temperature distribution is called infrared thermograph and the method to be called as infrared thermography.
- 33. Principle Every object whose surface temperature is above absolute zero radiates energy at a wavelength corresponding to its surface temperature. Utilizing our highly sensitive infrared cameras, it is possible to convert this radiated energy into a thermal image of the object being surveyed .
- 34. THERMOGRAPHIC CAMERA The camera converts radiated heat energy into an electrical signal which is then displayed on the monitor as a real-time heat image of the object being scanned.
- 36. ADVANTAGES It is a non-contact type technique. A large surface area can be scanned in no time. Presented in visual & digital form. Software back-up for image processing and analysis.
- 37. DISADVANTAGES Cost of instrument is relatively high. Unable to detect the inside temperature if the medium is separated by glass/polythene material etc. Difficult to interpret even with experience Training and staying proficient is time consuming
- 38. • Testing is not viable during periods of adverse weather (rain or wind). • Testing can be adversely affected by several surface conditions such as Water Wearing Discolouration Crack sealant Strong wind, etc.,
- 39. APPLICATIONS Printed circuit board evaluation and troubleshooting. Thermal mapping of semiconductor device services Circuit board component evaluation Production-type inspection of bonded structures Inspection of hybrid microcircuits Inspection of solder joints
- 40. Radiography Test • NDT method that utilizes x-rays or gamma radiation to detect discontinuities in materials, and to present their images on recording medium. • This includes X-rays, gamma rays and radio- isotopes. This method is used to check internal cracks, defects in materials which are made by casting, welding, forging. • Nowadays, radiography techniques are finding more extensive applications in the field of physical metallurgy and in the treatment of various diseases.
- 41. • Rays are absorbed by the materials through which they are passed in the proportion of their density. The rays, after passing through the components, show a picture on a fluorescent screen or on a photographic plate. • The cracks, blow holes and cavities appear lighter, whereas inclusions of impurities appear darker than the metal component. • Developed photographic film show lighter and darker areas to represent the radiograph of defects in the component.
- 43. Advantages of Radiography Test • X-ray radiography is highly sensitive, fast method of finding defects • X-ray radiography is suitable for various applications due to its adjustable energy levels • Gamma ray radiography has high penetrating power hence can be used for more denser and thicker materials • A number of samples can be inspected at a time by gamma ray radiography
- 44. Disadvantages of Radiography Test • X-ray radiography can be applied for thinner components due to its less penetrating power • X-ray radiography allows only one component to be tested at a time • X-ray radiography involves high initial cost • X-ray and gamma ray radiography involve radiations which are hazardous to living beings • Trained operators are required
- 45. Eddy Current Testing Basic Principle When coil carrying alternating current is brought near metallic specimen, eddy currents are developed in specimen due to electromagnetic induction. EMI depend on i)Magnitude and frequency of alternating current flowing in coil. ii) Electrical conductivity of specimen. iii) Magnetic permeability of specimen.
- 46. iv)Shape of specimen. v)Relative positions of coil and specimen. vi)Microstructure and hardness of Specimen. vii)Amount and type of defects in the specimen.
- 49. Advantages ECT • Test is quick and less time consuming • Test can be automated easily • Permanent record of test results can be easily available • Test is versatile and can be used for various applications
- 50. Disadvantages of ECT • The instrument standardization and calibration is necessary from time to time • Instruments and display units are costly • Test can be applied to components of limited size and shape
- 51. Ultrasonic testing • Ultrasonic testing uses high frequency sound energy to conduct examinations and make measurements. •Ultrasonic examinations can be conducted on a wide variety of material forms including castings, forgings, welds, and composites. •A considerable amount of information about the part being examined can be collected, such as the presence of discontinuities, part or coating thickness.
- 52. Basic Principles of Sound •Sound is produced by a vibrating body and travels in the form of a wave. •Sound waves travel through materials by vibrating the particles that make up the material. •The pitch of the sound is determined by the frequency of the wave (vibrations or cycles completed in a certain period of time). •Ultrasound is sound with a pitch too high to be detected by the human ear.
- 53. Spectrum of sound Frequency range Description Example (Hz) 0 - 20 Infrasound Earthquake 20 – 20,000 Audible sound Speech,music > 20,000 Ultrasound Quartz crystal
- 54. Ultrasound Generation • Ultrasound is generated with a transducer. • A piezoelectric element in the transducer converts electrical energy into mechanical vibrations (sound), and vice versa. • The transducer is capable of both transmitting and receiving sound energy.
- 55. • Ultrasonic waves are introduced into a material where they travel in a straight line and at a constant speed until they encounter a surface. • At surface interfaces some of the wave energy is reflected and some is transmitted. • The travel time of the sound can be measured and this provides information on the distance that the sound has travelled.
- 56. • Equipment for ultrasonic testing is very diversified. Proper selection is important to insure accurate inspection data as desired for specific applications. • In general, there are three basic components that comprise an ultrasonic test system: - Instrumentation - Transducers - Calibration Standards
- 57. Instrumentation •Ultrasonic equipment is usually purchased to satisfy specific inspection needs, some users may purchase general purpose equipment to fulfill a number of inspection applications. •Test equipment can be classified in a number of different ways, this may include portable or stationary, contact or immersion, manual or automated. •Further classification of instruments commonly divides them into four general categories: D-meters, Flaw detectors, Industrial and special application.
- 58. • D-meters or digital thickness gauge instruments provide the user with a digital (numeric) readout. • They are designed primarily for corrosion inspection applications. • Flaw detectors are instruments designed primarily for the inspection of components for defects. • However, the signal can be evaluated to obtain other information such as material thickness values.
- 59. • Industrial flaw detection instruments, provide users with more options than standard flaw detectors. • May be modulated units allowing users to tailor the instrument for their specific needs. • Generally not as portable as standard flaw detectors.
- 60. Transducers •Transducers are manufactured in a variety of forms, shapes and sizes for varying applications. •Transducers are categorized in a number of ways which include: - Contact or immersion - Single or dual element - Normal or angle beam •In selecting a transducer for a given application, it is important to choose the desired frequency, bandwidth, size
- 61. Contact Transducers • Contact transducers are designed to withstand rigorous use, and usually have a wear plate on the bottom surface to protect the piezoelectric element from contact with the surface of the test article. • Many incorporate ergonomic designs for ease of grip while scanning along the surface.
- 62. • Contact transducers are available with two piezoelectric crystals in one housing. These transducers are called dual element transducers. • One crystal acts as a transmitter, the other as a receiver.
- 63. Angle beam transducers • Angle beam transducers incorporate wedges to increase the versatility of transducer enabling it to become an angle transducerof 45,60 or 70 degrees. •Transducers can use fixed or variable wedge angles. •Common application is in weld examination.
- 64. Immersion transducers • Immersion transducers are designed to transmit sound whereby the transducer and test specimen are immersed in a liquid coupling medium (usually water). • Immersion transducers are manufactured with planar, cylindrical or spherical acoustic lenses (focusing lens).
- 65. Calibration • Calibration is a operation of configuring the ultrasonic test equipment to known values. This provides the inspector with a means of comparing test signals to known measurements.
- 66. • Information from ultrasonic testing can be presented in a number of differing formats. • Three of the more common formats include: A-scan B-scan C-scan
- 67. •A-scan presentation displays the amount of received ultrasonic energy as a function of time.
- 68. • B-scan presentations display a profile view (cross-sectional) of a test specimen. • Only the reflector depth in the cross-section and the linear dimensions can be determined.
- 69. The C-scan presentation displays a plan type view of the test specimen and discontinuities.
- 70. Test Techniques •Ultrasonic testing is a very versatile inspection method, and inspections can be accomplished in a number of different ways. •Ultrasonic inspection techniques are commonly divided into three primary classifications. –Pulse-echo and Transmission (Relates to whether reflected or transmitted energy is used) –Normal Beam and Angle Beam (Relates to the angle that the sound energy enters the test article) –Contact and Immersion (Relates to the method of coupling the transducer to the test article)
- 71. • In pulse-echo testing, a transducer sends out a pulse of energy and the same transducer listens for reflected energy (an echo). • Reflections occur due to the presence of discontinuities and the surfaces of the test article. • The amount of reflected sound energy is displayed versus time, which provides the inspector information about the size and the location of features that reflect the sound.
- 72. Through-Transmission • Two transducers located on opposing sides of the test specimen are used. One transducer acts as a transmitter, the other as a receiver. • Discontinuities in the sound path will result in a partial or total loss of sound being transmitted and be indicated by a decrease in the received signal amplitude. • Through transmission is useful in detecting discontinuities that are not good reflectors, and when signal strength is weak. It does not provide depth information.
- 73. Normal and Angle Beam • In normal beam testing, the sound beam is introduced into the test article at 90 degree to the surface. • In angle beam testing, the sound beam is introduced into the test article at some angle other than 90. • The choice between normal and angle beam inspection usually depends on two considerations: -The orientation of the feature of interest – the sound should be directed to produce the largest reflection from the feature. -Obstructions on the surface of the part that must be worked around.
- 74. • To get useful levels of sound energy into a material, the air between the transducer and the test article must be removed. This is referred to as coupling. • In contact testing a couplant such as water, oil or a gel is applied between the transducer and the part. • In immersion testing, the part and the transducer are place in a water bath. This arrangement allows better movement of the transducer while maintaining consistent coupling. • With immersion testing, an echo from the front surface of the part is seen in the signal but otherwise signal interpretation is the same for the two techniques.
- 75. Advantage of Ultrasonic Testing •Sensitive to both surface and subsurface discontinuities. •Depth of penetration for flaw detection or measurement is superior to other methods. •Only single-sided access is needed when pulse-echo technique is used. •High accuracy in determining reflector position and estimating size and shape. •Electronic equipment provides instantaneous results. •Detailed images can be produced with automated systems. •Has other uses such as thickness measurements, in addition to flaw detection.
- 76. Limitations of Ultrasonic Testing •Surface must be accessible to transmit ultrasound. •Due to manual operation, careful attention and highly skilled operators are required •Normally requires a coupling medium to promote transfer of sound energy into 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.
- 77. Application • Flaw detection(cracks,porosity etc.,) • Estimation of void content in composites and plastics • Thickness measurement of pipelines,reactor vessels
- 78. ACOUSTIC EMISSION TESTING • Acoustic emission may be defined as a transient elastic wave generated by the rapid release of energy within a material • When a structure is subjected to an external stimulus (change in pressure,load or temperature) ,localized source trigger the release of energy in the form of stress waves, which propogate to the surface and recorded by sensors.
- 80. Testing process • Detection of AE • Processing of AE signals • Displaying AE signals • Locating AE signals
- 81. Testing process
- 82. Detection of AE • As crack grows a number of emissions are released • When the AE wave arrives at the surface of test specimen minute movement of surface molecules occur • The function of AE sensor is to detect this movement and convert it into electrical signal
- 83. Processing of AE signals The small voltage generated by the sensor is amplified and radio frequency signal is transmitted to the computer The RF signal is split into discrete waveforms These waveforms are then prescribed by characteristics such as amplitude,rise time,absolute energy
- 84. Displaying AE signals The collected wave forms can then be displayed in two ways One,function of waveform parameters Two,as collected waveform Most AE tests currently only record the waveform parameters and ignore the collected waveform, mainly due to large amount of computing memory it uses
- 85. Locating AE signals The predominant method of source location is based on the time difference between the arrival of individual AE signals
- 86. Advantages High sensitivity Early and rapid detection of defects,flaws,cracks etc., Real time monitoring Minimization of plant downtime for inspection,no need for scanning the whole structural surface.
- 87. Disadvantages • Acoustic emission systems can only estimate qualitatively how much damage is in the material and approximately how long the components will last .So,other methods are still needed to do more thorough examinations and provide quantitative results.
- 88. Applications • Inspect and monitor pipelines,storage tanks,bridges and variety of composite and ceramic components. • Also used in process control applications such as monitoring welding process