Analysis of Platen Superheater Tube Degradation in Thermal Power Plants via Destructive/Non-Destructive Characteristic Evaluation.

Coal-fired power plants operating under Korea's standard supercritical pressure operate in a high-temperature environment, with steam temperatures reaching 540 °C. A standard coal-fired power plant has a 30-year design life, and lifespan diagnosis is performed on facilities that have operated for more than 100,000 h or 20 years. Visual inspection, thickness measurements, and hardness measurements in the field are used to assess the degree of material degradation at the time of diagnosis. In this study, aging degradation was assessed using an electromagnetic acoustic transducer to measure the change in transverse ultrasonic propagation speed, and the results were compared to microstructural analysis and tensile test results. Based on the experimental results, it was found that the boiler tube exposed to a high-temperature environment during long-term boiler operation was degraded and damaged, the ultrasonic wave velocity was reduced, and the microstructural grains were coarsened. It was also confirmed through tensile testing that the tensile and yield strengths increased with degradation. Our findings prove that the degree of change in mechanical properties as a function of the material's degradation state is proportional to the change in ultrasonic wave velocity.

Torsional wave experiments with a new magnetostrictive transducer configuration.

For the efficient long-range nondestructive structural health inspection of pipes, guided waves have become widely used. Among the various guided wave modes, the torsional wave is most preferred since its first branch is nondispersive. Our objective in this work is to develop a new magnetostrictive transducer configuration to transmit and receive torsional waves in cylindrical waveguides. The conventional magnetostrictive transducer for the generation and measurement of torsional waves consists of solenoid coils and a nickel strip bonded circumferentially to test pipes. The strip must be premagnetized by a permanent magnet before actual measurements. Because of the premagnetization, the transducer is not suitable for the long-term on-line monitoring of pipes buried underground. To avoid the cumbersome premagnetization and to improve the transduction efficiency, we propose a new transducer configuration using several pieces of nickel strips installed at 45 degrees with respect to the pipe axis. If a static bias magnetic field is also applied, the transducer output can be substantially increased. Several experiments were conducted to study the performance of the proposed transducer configuration. The proposed transducer configuration was also applied for damage detection in an aluminum pipe.