• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.100-107
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• 1999

Due to the high temperature and pressure, the materials of pipeline in power plant are degraded by creep damage. So far, many conventional measurement techniques such as replica method, electric resistance method, adn hardness test method for creep damage have been used. Among them, the replica method has mainly been used for the inspection of components. But this technique is restricted to the applications at the surface of the objects and cannot be used to material inside. In this paper, the measuring methods of evaluation by using ultrasonic attenuation and electric resistance for the creep detection of creep damage in the form of cavities on grain boundaries or intergranular microcracks were carried out. Absolute measuring method of quantitave ultrasonic attenuation technique for 1Cr0.5Mo material degradation was analyzed for determining the creep degradation steps using life prediction formula. As a result of measurement for creep specimens, we founded that the coefficient of utrasonic attenuation was increased as the increase of creep life fracton(${phi}c$) and the decreasing rate of wlwctric resistance was also increased.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.11
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• pp.1887-1893
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• 2016

The VSA(Video Signal Analysis) method is the time-domain approach for estimating ultrasonic attenuation which utilizes the envelop signals from backscattered rf signals. The echogenicity of backscattered ultrasonic signals, however, from deeper depths are distorted when the broadband transmit pulse is used and it degrades the estimation accuracy of attenuation coefficients. We propose the modified VSA method using adaptive bandpass filters according to the centroid shift of echo signals as a pulse propagates. The technique of dual-reference diffraction compensation is also proposed to minimize the estimation errors because the difference of attenuation properties between the reference and sample aggravates the estimation accuracy when the differences are accumulated in deeper depth. The proposed techniques minimize the distortion of relative echogenicity and maximize the signal-to-noise ratio at the given depth. Simulation results for numerical tissue-mimicking phantoms show that the Rectangular-shaped filter with the appropriate center frequency exhibits the best estimation performance and the technique of the dual-reference diffraction compensation dramatically improves accuracy for the region after the beam focus.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.10
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• pp.78-85
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• 2004

The particle amount monitoring technique using ultrasound is proposed to determine the proper maintenance time of the filter in the supply process of pure gas in the unit of oxygen plant. There are advantages that it is adaptable in high temperature and high pressure, and it is not disturbed by being exposed in the gas flow, and it can be implemented very economically. The applicability of the ultrasonic technique is pre-studied through the theoretical analysis for the dependency of attenuation of ultrasonic wave on the particles in the gas flow. For the purpose, absorption, scattering and dispersion models are considered, and the attenuation by absorption and the change rate of the propagation speed are calculated fur the specific range of particle size and the ultrasonic wave frequency. It was expected by simulation that the absorptive attenuation by particles was the most sensitive to the change of particle amount. The experimental result showed high correspondence with the theoretical expectation so that this ultrasound attenuation measurement was proved to be highly effective for monitoring the amount of floating particles in the gas flow.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.3
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• pp.279-284
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• 2008

The firmness of fruit is one of the most important quality factors and is highly correlated to the elastic modulus. In this study, the ultrasonic transmission method was applied to evaluate the elastic modulus of the apple. In order to transmit and receive the ultrasonic wave through the whole apple, the ultrasonic measurement setup consisted of ultrasonic pulser, two specially fabricated ultrasonic transducers for fruit and digital storage oscilloscope. Ultrasonic parameters such as ultrasonic wave velocity, apparent attenuation, and peak frequencies were analyzed. The elastic modulus of apple was measured by using compression test apparatus. The correlations between ultrasonic parameters and elastic modulus were analyzed. A multiple linear regression model describing the relationship between elastic modulus and ultrasonic parameters was proposed.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.487-495
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• 2005

Mechanical properties of in-service facilities are required to evaluate the integrity of power plants and chemical plants. Non-destructive technique can be used to evaluate the mechanical properties. To investigate the mechanical properties using ultrasonic technique, the four classes of thermally aged specimens were prepared using an artificially accelerated aging method. Ultrasonic tests, tensile tests, fracture toughness tests, and hardness tests were performed for the specimens. Then the mechanical properties were compared with ultrasonic parameters such as attenuation and non-linear parameter. From the investigation, we confirm that the ultrasonic parameter can be used to evaluate the mechanical properties.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.17-24
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• 2002

The objective of the present research is to evaluate the wave propagation velocity and attenuation characteristics of kaolin clay specimens using ultrasonic testing. Test specimens with known initial micro-fabric were prepared using a two-stage slurry consolidation technique. For a known state of stress conditions, initial void ratio, and micro-fabric, a series of experiments were conducted to evaluate the longitudinal wave propagation velocity and associated damping behavior. The effects of major variables involved in ultrasonic testing of cohesive soil were considered in this study. Ultrasonic velocity was not correlated to the microfabric structure under the given consolidated pressure whereas ultrasonic attenuation was affected by the microstructural properties of the specimen.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.1-6
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• 2013

Ultrasonic guided wave techniques have been widely used for long range nondestructive detection in tube-like structures. The present paper investigates the ultrasonic linear and nonlinear parameters for evaluating the thermal damage in aluminum pipe. Specimens were subjected to thermal loading. Flexible polyvinylidene fluoride (PVDF) comb transducers were used to generate and receive the ultrasonic waves. The second harmonic wave generation technique was used to check the material nonlinearity change after different heat loadings. The conventional linear ultrasonic approach based on attenuation was also used to evaluate the thermal damages in specimens. The results show that the proposed experimental setup is viable to assess the thermal damage in an aluminum pipe. The ultrasonic nonlinear parameter is a promising candidate for the prediction of micro-damages in a tube-like structure.

• Journal of Biosystems Engineering
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• v.28 no.3
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• pp.239-244
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• 2003

The potential use of ultrasonic technique for firmness measurement of apples was evaluated. Mechanical properties(bioyield deformation, bioyield strength, rupture deformation, ultimate strength, and elastic modulus) and ultrasonic parameters (ultrasonic velocity, attenuation coefficient and the first peak frequency) of the apple flesh during the storage time were measured and analyzed. Ultrasonic parameters were determined from the measurement of ultrasonic wave transmission through the apple flesh specimen. Mechanical properties were obtained by universal testing machine. The bioyield strength, rupture strength, elastic modulus, ultrasonic velocity, and the first peak frequency of the apple flesh decreased with the storage time. The bioyield deformation, rupture deformation, and ultrasonic attenuation coefficient increased with the storage time. The correlation analysis between ultrasonic parameters and mechanical properties and the storage time was performed. The high correlations were found between the storage time and the ultrasonic parameters, and these relationships seem to be useful for determining the firmness of the apple flesh.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.127-132
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• 2003

In a today industry, the welding is doing a many portion in structure manufacture. This study is simulated heat of heat-effected zone and researched a mechanical properties and ultrasonic characteristic in used the SS400 and the STS304. As the result mechanical properties of steel that become drawing decreased because of remaining stress by strain gardening according as simulated heat temperature rises, but according as temperature rises in material that do simulated heat after have done annealing, mechanical propensity was improved. The velocity and attenuation become different by effect of remaining stress than effect of material internal microstructure in ultrasonic wave test. In the case of STS304, there was change in mechanical properties by effect that is by strain hardening, but there was no change in material that simulated heat after annealing. When become drawing in ultrasonic waves test, according as simulated heat temperatures rise, change of attenuation coefficient is looked, but material that simulated heat after annealing was no change almost both the volocity and attenuation.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.205-211
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• 2013

This paper studies on mechanical properties, fractures, and ultrasonic characteristics of Pure Titanium welds using ultrasonic attenuation. Ti specimen was made by using AR purge gas. When the titanium weld specimen is fractured, Tensile tests were conducted in order to observe the ultrasonic signal changes. A scanning electron microscope(SEM) was used to observe changes in failure surface and an ultrasonic normal probe with the central frequency of 4 MHz was used to obtain ultrasonic signals. As a result, the value of the mechanical properties in the weld zone was lower than that in the base zone and heat affected zone(HAZ) from Ti. Also the grain size in the weld zone was bigger than that in the weld zone and HAZ from Ti. Ultrasonic signals using a RMS method presents correlation between envelope area and the tensile strength. Consequently, the ultrasonic method could be potential tool for integrity evaluation of the Ti weld zone.