The purpose of this research is to identify and recommend methods of inspection, surveillance, and monitoring that would provide timely detection of valve degradation and service wear so that maintenance or replacement could be performed prior to loss of safety functions. This research is focused on the capability of acoustic emission (AE) technique to provide diagnostic information on the determination of check valve aging and degradation, check valve failures and undesirable operating modes. Several commercially available check valve diagnostic-monitoring methods were evaluated, especially for the techniques based on measurements of acoustic emission, ultrasonic, and accelerometers. In the present paper, acoustic emission signals due to leak from check valve with artificially leakage and artificially worn disk were studied both analytically and experimentally. The results of development of advanced signal processing and de-noising techniques also have been presented.
This study presents an approach to leak detection of pipeline review in terms of theoretical analysis such as acoustics and hydromechanics that should be accompanied by explanation of leakage. The acoustic emission signals during leak from circular hole of different geometries were studied both analytically and experimentally. The relationships between acoustic parameters and fluid mechanical parameters also were derived analytically. A quadrupole aerodynamic model was applied for the analysis of leak from the circular hole. Computer simulation results demonstrate the effectiveness of the proposed approach. In addition, it was confirmed that the wavelet transform (WT) was an effective tool to determine source location. That is, arrival times of each frequency component needed in the velocity calculation could be determined from the peak of the magnitude of wavelet transform data on the time-frequency plane.
Pipelines of nuclear power plants undergo high pressure and temperature. Thermal stratification typically occurs in the surge line and the main feed water lines by flow and this stratification will initiate and propagate thermal fatigue cracks. This may cause rupture and leakage and it is a serious problem to nuclear power plants operation. Therefore it is very important to detect and measure thermal fatigue cracks. In this study, thermal fatigue cracks were generated in austenitic stainless steel specimens by a thermal cycle in notched pipes and weld jointed pipes. Ultrasonic techniques were used to evaluate the thermal fatigue crack depth. When ultrasonic waves propagate from an angle beam probe to thermal fatigue cracks, waves are reflected and diffracted. Crack depth was evaluated by the reflected signals from back wall and diffracted signals from the crack tip, but diffracted signals were too weak to detect so the reflected signals were more useful. The TOFD and dB drop methods were used in this study. The TOFD method is uses a time delay of diffracted signal from the crack tip. The dB drop method is an application of an amplitude decreasing rate by a probe moving distance.
Fractures of mechanical components and structures are often produced by initiation and propagation of fatigue cracks. Especially, in the case of aircrafts, since fatigue failure generally was caused by an invisible small crack, it is necessary to detect an initial crack during in-service inspection. The purpose of this research is to identify and recommend methods of inspection that would provide timely detection of fatigue failures. In this paper, acoustic emission (AE) technique has been used to detect fatigue crack. Acoustic emission technique is very useful to prevent catastrophic failure of large scale structures with unknown discontinuities such as fatigue crack. This research is focused on the capability of AE technique to provide diagnostic information to detect fatigue crack growth and initiation under cyclic loading. The coldworked 2024-T351 and 7050-T7451 aluminum alloys are used for this study and these alloys usually applied in aircraft primary members.
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