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

Se-Beom Oh,Dong-Seok Yun,Jongbeom Kim,Dong-Wook Kim,Kyung-Mo Kim,Soon-Woo Han

doi:10.3390/ma15020581

Abstract

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.

Highlights

Accepted: 4 January 2022Since the late 1980s, the design of coal-fired power plants has been standardized in theKorea as a strategy for building high-quality, large-scale power plants in a short period of time, laying the groundwork for self-reliance in comprehensive design and manufacturing technologies for power plants [1]
With a steam pressure of 255 kg/cm2 entering the turbine and a steam temperature of 541 ◦ C, supercritical pressure standard coal-fired power plants operate at high temperatures and pressures
Because platen superheater (PSH) tubes in standard coal-fired power plants operate at high temperatures and pressures, X20CrMoV12.1 was used, which has excellent high-temperature oxidation resistance and creep strength characteristics

Summary

Introduction

Accepted: 4 January 2022Since the late 1980s, the design of coal-fired power plants has been standardized in theKorea as a strategy for building high-quality, large-scale power plants in a short period of time, laying the groundwork for self-reliance in comprehensive design and manufacturing technologies for power plants [1]. With a steam pressure of 255 kg/cm entering the turbine and a steam temperature of 541 ◦ C, supercritical pressure standard coal-fired power plants operate at high temperatures and pressures. The superheater, in particular, is a facility that generates superheated steam by heating steam evaporated from the boiler’s water-cooling wall to raise the steam temperature, and it operates at high temperatures and pressures in the boiler tube. The reason for this is that the power plant’s thermal efficiency improves as the steam pressure and temperature increase [5]. As the superheated steam is used, the turbine’s thermal drop increases, its internal efficiency increases, the friction loss between the turbine and the steam supply pipe decreases, and the erosion by moisture

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Conclusion