Acoousitc emmison testing in non destcruve testing.pptx

accoustic emmison testing in ndt
Acoustic emission testing (AET) is a non-destructive method that detects and analyzes defects in materials by listening to the sounds they make when stressed:
How it works
When a material is stressed, it releases energy in the form of ultrasonic waves. These waves propagate through the material and are detected by sensors placed on the surface or near the material. The sensors convert the vibrations into electrical signals, which are then analyzed to identify the type and location of any defects.
What it can detect
AET can detect a variety of defects, including cracks, corrosion, fiber delamination, and more.
When it's used
AET is used in many industries, including construction, automotive, aerospace, and oil and gas. It's especially useful for monitoring the safety of structures like bridges, pipelines, and pressure containers.
Advantages
AET has several advantages over other inspection methods, including:
It doesn't require dismantling components or removing oil
It doesn't contaminate with water
It doesn't require disposal of test fluids
Limitations
AET can't be used on extra thick metallic structures or some highly absorptive or transparent materials.
Comprehensive Guide to Acoustic Emission Testing - Flyability
Acoustic emission testing is an inspection method that uses the release of ultrasonic stress waves to identify defects in material...

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Acoustic emission - Wikipedia
The three major applications of AE techniques are: 1) source location – determine the locations where an event source occurred; 2)

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Acoustic Emission Testing (AET) | Inspectioneering

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Acoustic emission (AE) testing is a non-destructive testing (NDT) technique that detects and monitors the release of ultrasonic stress waves from localised sources when a material deforms under stress.Acoustic emission testing is an inspection method that uses the release of ultrasonic stress waves to identify defects in materials. These ultrasonic waves are not introduced from an external source, as they are in ultrasonic testing, but rather originate from within the material being inspected.When a load applied to a structure gradually increases, some microscopic deformations may occur, resulting in elastic waves propagating through the target surface. Then, these elastic waves are detected and converted to voltage signals by an AE sensor mounted on the structure's surface.Acoustic emission testing (AET) measures transient elastic waves produced by a test object under external stimuli like pressure, load, or temperature changes. Elastic waves cause mechanical vibrations. AE sensors placed on the test object's surface or held close to it convert these vibrations into electrical signals.Acoustic emissions can be detected in frequency ranges under 1 kHz, and have been reported at frequencies up to 100 MHz, but most of the released energy is within the 1 kHz to 1 MHz range. Rapi

1. UNIT-V Acoustic     emission techniques:    Principles of acoustic     emission techniques technique Instrumentation Sensitivity Applications.

2. Acoustic Emission Testing (AET)  is a non destructive testing method that is based on the generation of waves produced by a sudden redistribution of stress in a material. When a piece of equipment is subjected to an external stimulus , such as a change in pressure, load or temperature , this triggers the release of energy in the form of stress waves, which propagate to the surface and are recorded by sensors. Acoustic emissions can come from natural sources, such as earthquakes or rock bursts or from the equipment itself such as melting, twinning, and phase transformations in metals. Acoustic emission testing involves the detection and analysis of AE signals using specialized equipment and can provide information on the origin and  significance of discontinuities in a material .

3. Acoustic emission testing is different than other NDT techniques in two major ways: 1. Instead of supplying energy to the object under examination, AET listens for the energy released by the object naturally . AE tests can be performed on structures while they are in operation since this provides adequate loading for propagating defects and triggering acoustic emissions. 2. AET deals with dynamic processes in a material. This is particularly useful because only active features are highlighted during the examination. Thus, it is possible to discern between developing and stagnant defects . However, it is possible for flaws to go undetected if the loading isn’t high enough to cause an acoustic event that can be detected by the system.

4. Acoustic emission testing is most often used in a dynamic test environment, meaning that it is used to monitor for crack detection in pressure equipment when the equipment is experiencing an increase in stress . AET systems generally contain a sensor, preamplifier, filter, and amplifier, along with measurement, display, and storage equipment . Acoustic emission sensors respond to any dynamic motion caused by an acoustic emission event. This is achieved through transducers that convert mechanical movement into an electrical voltage signal . The majority of AET equipment responds to movement in a range of 30 kHz to 1 MHz in brittle and ductile material. For materials with high attenuation, such as plastic composites, lower frequencies may be used to better distinguish acoustic emission signals.

5. Because of its versatility, acoustic emission testing has many applications across a variety of industries. ONLINE MONITORING OF PRESSURE VESSELS, PIPELINES AND ENGINEERING STRUCTURES. ii) LEAKAGE DETECTION and location iii) Quality control during fabrication. iv) Monitoring underground pipelines v) Online weld monitoring In O&G and chemical processing industries, AET is often used to assess structural integrity, test for leaks, monitor weld quality, and detect active flaws such as corrosion in the bottom of aboveground storage tanks or creep damage in high energy piping systems.

6. The genesis of today’s technology in AE was the work of Josep Kaiser. In 1950 Kaiser published his thesis where he reported the first comprehensive investigation into the phenomenon of AE. Kaiser used tensile tests of conventional engineering materials to determine : Types of noises generated from within the specimen. The acoustic processes involved. The frequency ranges and amplitude levels found. The relation between stress, strain and the frequencies recorded at various stress levels to which specimens were subjected to.

7. Acoustic emission (AE) is high frequency elastic Waves produced in a material under load by the rapid release of strain energy during crack propagation, plastic deformation or phase transformation. The Waves travel to the surface where they can be listened (detected). This technique is also called stress wave emission AE Can be considered as extension of ultrasonic testing, except that the ultrasonic waves are replaced with acoustic waves. AE can give indications on the location and the relative severity of a defect. AE can be used to measure degree of stress (strain) of a material.

8. Principle of AET : Acoustic emission inspection detects and analyses minute AE signals generated by growing discontinuities in material under a stimulus such as stress and temperature. Proper analysis of these signals can provide information concerning the detection and location of these discontinuities and the structural integrity. Another important feature of AE is its irreversibility. If a material is loaded to a given stress level and then unloaded, usually no emission will be observed upon immediate reloading until the previous stress has been exceeded. This is known as Kaiser effect and is due to the fact that AE is closely related to plastic deformation and fracture.

9. Amplitude and Duration of AE Signal Kaiser effect.

10. Advantages : Real time detection of component failure. Highly accurate results . Sensitive Economical Early warning of crack growth Exact location of defect can be found. Possible to test pressure equipment during plant operation. Can detect very small flaws (1 to 50 microns) Disadvantages : Sophisticated and high initial cost - as detected signal has low energy Required skill person to operate and understand signals. Difficult for outdoor use.

11. Weld Monitoring : - During the welding process, temperature changes induce stresses between the weld and the base metal. These stresses are often relieved by heat treating the weld.  However, in some cases tempering the weld is not possible and minor cracking occurs. Amazingly, cracking can continue for up to 10 days after the weld has been completed. Using stainless steel welds with known inclusions and accelerometers for detection purposes and background noise monitoring, it was found by W. D. Jolly (1969) that low level signals and more sizeable bursts were related to the growth of micro-fissures and larger cracks respectively. ASTM E 749-96 is a standard  practice of AE monitoring  of continuous welding.

12. Bucket Truck (Cherry Pickers) Integrity Evaluation : Accidents, overloads and fatigue  can all occur when operating bucket trucks or other aerial equipment. If a mechanical or structural defect  is ignored, serious injury or fatality can result. In 1976, the Georgia Power Company pioneered the aerial man lift device inspection. Testing by independent labs and electrical utilities followed. Although originally intended to examine only the boom sections, the method is now used for inspecting the pedestal, pins, and various other components. Normally, the AE tests are second in a chain of inspections which start with visual checks. If necessary, follow-up tests take the form of magnetic particle, dye  penetrant , or ultrasonic  inspections. Experienced personnel can perform five to ten tests per day, saving valuable time and money along the way. ASTM F914 governs the procedures for examining insulated aerial personnel devices.

13. Gas Trailer Tubes : - Acoustic emission testing  on pressurized jumbo tube trailers was authorized by the Department of Transportation in 1983. Instead of using hydrostatic retesting, where tubes must be removed from service and disassembled, AET allows for in situ testing. A 10% over-pressurization  is performed at a normal filling station with AE sensors attached to the tubes at each end.  A multichannel acoustic system is used to detection and mapped source locations.  Suspect locations are further evaluated using ultrasonic  inspection, and when defects are confirmed the tube is removed from use.  AET can detect subcritical flaws whereas hydrostatic testing cannot detect cracks until they cause rupture of the tube. Because of the high stresses in the circumferential  direction of the tubes, tests are geared toward finding longitudinal  fatigue  cracks.

14. Bridges : - Bridges contain many welds, joints and connections, and a combination of load and environmental factors heavily influence damage mechanisms such as fatigue  cracking and metal  thinning due to corrosion.  Bridges receive a visual inspection about every two years and when damage is detected, the bridge is either shut down, its weight capacity is lowered, or it is singled out for more frequent monitoring.  Acoustic Emission is increasingly being used for bridge monitoring  applications because it can continuously gather data and detect changes that may be due to damage without requiring lane closures or bridge shutdown. In fact, traffic flow is commonly used to load or stress  the bridge for the AE testing.

15. Applications

16. Applications

17. Acoustic Emission - Technique With the equipment configured and setup complete, AE testing may begin. The sensor is coupled to the test surface  and held in place with tape or adhesive. An operator then monitors the signals which are excited by the induced stresses in the object. When a useful transient or burst signal is correctly obtained, parameters like amplitude, counts, measured area under the rectified signal envelope (MARSE), duration, and rise time can be gathered. Each of the AE signal feature shown in the image is described below.

18. Ring down counts is the number of times the signal crosses the threshold level set for eliminating background noise. This could be used independently or as the cummlative counts with respect to time or any other parameter. Count rate is another parameter commonly used. The most common ways in which AE signals can be processed are : Ringdown counts, ringdown count rates, events. Energy analysis : continuous and burst type emissions. Amplitude analysis : characterise emissions from different processes. Frequency analysis : identify different types of failures. Advanced signal analysis concepts – pattern recognition, spectral analysis, etc.

19. On large pressure vessels – necessary not only to detect AE signals but also to locate their sources. By suitably placing several sensors over the surface of a pressure vessel and monitoring the time of arrival of the signals to various sensor locations. Because of high velocity of sound and relative closeness of sensors on a steel vessel, time resolutions in microsecond range must be made in order to locate the source to within less than about 25mm. AET is capable of locating one or more discontinuities while they are growing. When the discontinuity approaches a critical size the AE count rate increases markedly thus giving a warning for instability and failure of the component. AE evaluation of structure depends on the ability to detect weak signals in noisy electrical and mechanical environment. Proper instrumentation and effective methods are needed to discriminate between wanted and unwanted signals.

20. Instrumentation : AET consists of signal detection, data acquisition, processing and analysis units. The choice of analysing unit depends on the purpose for which AET is employed, the level of sensitivity required and economic consideration. Transducer for AET : Transducer for detection and recording of AE are piezoelectric transducer with frequency of the order of 30kHz to 2 MHz. Resonant type are used for narrow band instrumentation and non-resonant type with wide band instrumentation. Pre-amplification and filtering : The pre-amplifier follows the transducer . It should have low noise , moderately high power gain and input impedance matching the transducer. Filters are designed for different band widths in order to meet specific requirements. Post-amplification and threshold : The output of pre amplifier is very low and hence has to be amplified further before handling with the processing circuitry. In order to eliminate the background noise from analysis only signals exceeding certain threshold voltage are detected and analysed. Data acquisition :2 types of systems are in common use for acquisition of raw AE data for off line analysis, namely video recorder and analog magnetic recorders. When real time decision making is important with capability of on-line processing and analysis, transient recorders with computer interface are used. Processing and analysis : The processing instrumentation required for AET depends on the form and quality of raw data. Its function is to convert analog data to digital form. Display devices : Variety of display devices are used for displaying and recording analysed data. The simplest and most commonly used recording device is the X-Y recorder.

21. Sensitivity : AE inspection is extremely sensitive with other NDT methods. The minimum detectable crack for UT, RT and ECT methods is about 0.5mm if using ideal conditions. AET can detect crack growth of the order of 25 microns.

22. Amplitude A , is the greatest measured voltage  in a waveform and is measured in decibels (dB). This is an important parameter in acoustic emission inspection because it determines the detectability of the signal. Signals with amplitudes below the operator-defined, minimum threshold  will not be recorded. Rise time, R,  is the time interval between the first threshold  crossing and the signal peak. This parameter is related to the propagation  of the wave between the source of the acoustic emission event and the sensor. Therefore, rise time is used for qualification of signals and as a criterion for noise  filter. Duration, D , is the time difference between the first and last threshold  crossings. Duration can be used to identify different types of sources and to filter  out noise. This parameter relies upon the magnitude of the signal and the acoustics of the material.

23. MARSE, E , sometimes referred to as energy counts, is the measure of the area under the envelope of the rectified linear voltage  time signal from the transducer. This can be thought of as the relative signal amplitude  and is useful because the energy of the emission can be determined. MARSE is also sensitive to the duration and amplitude  of the signal, but does not use counts or user defined thresholds and operating frequencies. MARSE is regularly used in the measurements of acoustic emissions. Counts, N , refers to the number of pulses emitted by the measurement circuitry if the signal amplitude  is greater than the threshold. Depending on the magnitude of the AE event and the characteristics of the material, one hit may produce one or many counts. While this is a relatively simple parameter to collect, it usually needs to be combined with amplitude  and/or duration measurements to provide quality information about the shape of a signal.