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The properties in new tubes, tubes artificially saturated with hydrogen, and the radiant section of boiler tubes after long operations are studied. All samples are made of steel 20 according to the same technical conditions and subjected to identical heat treatment modes. The process of embrittlement is evaluated by detecting changes in the microstructural structure and in mechanical properties of the steel revealing the mechanism of hydrogen attack. Artificially hydrogen-saturated tubes do not exhibit decarbonization typical of naturally saturated tubes. These samples also exhibit a decrease in the limit of the rupture strength. Different types of fracturing are observed in tube samples: tubes having artificial hydrogen saturation show transcrystalline fracturing; intercrystalline fractures develop in the naturally saturated samples. At the same time, the fracture parameters (featuring hydrogen embrittlement areas) and the average concentrations of accumulated hydrogen in artificially hydrogen charged tubes and in tubes charged with hydrogen during operations are identical. Significant differences in the physical and mechanical properties are observed in all three types of tubes, making it impossible to apply the results obtained in model samples artificially saturated with hydrogen to real operating components.

This study investigates the failure of a carbon steel boiler tube (SA210 Grade A1) through a comprehensive metallurgical and mechanical analysis. Visual inspection revealed a localized deformation characterized by a thin lip failure with internal bulging. Sectioned tube samples showed brown and black deposits on the inner diameter (ID), which were confirmed as iron oxide through EDS analysis. Microstructural examination near the damaged region (within 25 mm) revealed extensive pearlite disintegration, creep voids, cracks, and carbide precipitates along ferrite grain boundaries, indicating exposure to high temperatures. SEM-EDS analysis further validated the presence of creep-induced damage and precipitate formation. Compared to unaffected regions, a significant reduction (− 18%) in hardness near the failure zone supported the observed microstructural degradation. Beyond 25 mm from the damage site, the tube retained its original ferrite–pearlite structure. Chemical composition analysis confirmed conformity with the SA210 Grade A1 specification. The evidence collectively indicates that the tube failure resulted from localized short-term overheating, leading to creep damage, material softening, and eventual rupture. This study highlights the importance of monitoring temperature excursions to prevent premature failures in high-temperature boiler components.

Steam generation is an essential process in steel production. Saturated steam is used in the cold-rolling mills of sample steel company to raise the acid pool temperature. The studied water-tube boiler had a rated saturated steam generation capacity of 47 tons per hour. This study used energy and exergy balance equations for each of the components in the cycle to calculate exergy efficiency and irreversibility rate. Results from the exergy analysis along with the exergy dissipation rate of the cycle were obtained. Based on the literature results, it was recommended to increase the input air temperature by means of a preheater. First, the exergy dissipation in the boiler was reduced by 68 kJ kg−1 with the installation of an economizer. The most important cause of exergy destruction was then presented, and some recommendations were provided on how to increase the temperature of the makeup water in order to increase the boiler efficiency and exergy.

In thermal power generation equipment, circumferential cracking in boiler tubes due to thermal cycling is a problem. Circumferential cracks form in the water-wall tube where sulfide corrosion occurs and in superheater and reheater tubes where high-temperature oxidation occurs. The main cause of the crack formations is thermal cycling, but sulfide corrosion and high-temperature oxidation also promote crack generation and accelerate crack progression. Therefore, preventing sulfide corrosion and/or high-temperature oxidation is one strategy for suppressing circumferential cracking. The authors previously developed a SiO2/TiO2/Al2O3-based/TiO2 coating for preventing sulfide corrosion and high-temperature oxidation on boiler tubes. In this work, to confirm the robustness and durability of the coating against circumferential cracking, laboratory experiments and exposure tests in actual power plants were performed. When applied to circumferentially cracked boiler tubes, the coating did not crack and suppressed growth of existing circumferential crack in comparison with an uncoated part.

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.

The present case study involves a thorough and methodical metallurgical analysis of a failed water wall tube to identify sulfidation corrosion as the cause of failure. The investigation into the failure of the water wall tube was conducted through various methods, including visual observation, chemical analysis, examinations using optical and scanning electron microscopy, fractography and surface analysis via SEM–EDS, x-ray diffraction analysis of deposits and reaction products, and evaluation of mechanical properties. The water wall tube exhibited failure in the form of an elliptical puncture, with no significant thinning at the location of the puncture. The chemical composition, mechanical properties, and microstructure of the failed water wall tube were in accordance with the specified standards for SA 210 grade C steel. The microstructure of the tube consisted of a ferrite–pearlite structure and showed no anomalies related to microstructure. The experimental results revealed that the tube failed due to sulfidation corrosion on its outer surface. This sulfidation reaction was initiated by sulfur from pyrite (FeS2) in the coal-ash deposits on the outer surface. Moreover, the buildup of ash deposits caused localized overheating, which accelerated the sulfidation reaction, followed by an oxidation reaction.

The development of a cost-effective and accurate model for predicting the fatigue life of materials is essential for designing thermal power plants and assessing their structural reliability under operational conditions. This paper reports a novel energy-based approach for developing unified models that predict the fatigue life of boiler tube materials in ultra-supercritical (USC) power plants. The proposed method combines the Masing behavior with a cyclic stress–strain relationship and existing stress-based or strain-based fatigue life prediction models. Notably, the developed models conform to the structure of the modified Morrow model, which incorporates material toughness (a temperature compensation parameter) into the Morrow model to account for the effects of temperature. A significant advantage of this approach is that it eliminates the need for tensile tests, which are otherwise essential for assessing material toughness in the modified Morrow model. Instead, all material constants in our models are derived solely from fatigue test results. We validate our models using fatigue data from three promising USC boiler tube materials—Super304H, TP310HCbN, and TP347H—and their welded joints at operating temperatures of 500, 600, and 700 °C. The results demonstrate that approximately 91% of the fatigue data for all six materials fall within a 2.5× scatter band of the model’s predictions, indicating a high level of accuracy and broad applicability across various USC boiler tube materials and their welded joints, which is equivalent to the performance of the modified Morrow model.

Welding distortions, assembly errors, and deviation correction between the welding torch and weld beads play a significant role in the automatic welding system of the boiler tube wall cladding. As a result, this paper proposes a seam tracking system comprised of two parts: a contact displacement sensor for data acquisition and an adaptive neuro-fuzzy inference system (ANFIS) controller along with the backpropagation (BP) algorithm for controlling the position and posture of the welding torch. The results showed that the proposed ANFIS controller achieves a faster rise time of up to 0.06 s, settling time of about 0.1 s, overshooting up to 1.5%, and amplitude stability with the lowest training error up to 2 × 10 −4  mm. In contrast, the fuzzy logic controller achieves a rise time of up to 0.075 s, a settling time of around 0.3 s, and a 0.5% overshoot. Also, the proportional–integral–derivative (PID) controller executes a lower rise time of up to 0.035 s, a settling time of about 0.25 s, and an overshoot of up to 9.34%. According to the results, the ANFIS controller performs better than the PID and fuzzy logic controllers. Thus, the proposed system offers a much-improved functionality in terms of flexibility, consistency, and cladding layer surface finish of the treated components. It fully meets the requirements of the welding torch control motion for seam tracking. It can also be used to create automatic seam tracking systems for other types of surface treatment.

Corrosion failure of materials often exposed to the corrosive environment in district heating systems is critical for operation and maintenance of the facility. It is important to establish a prevention method from an accurate prognosis on the cause of the corrosion failure. In this study, a failure analysis on the water wall boiler tube in a district heating system was carried out. The fracture occurred in an open window shape with a significant internal wall thinning that formed Na- and Fe-oxide by caustic corrosion. Tensile residual stress in the hoop direction developed inside the tube weakened the protective magnetite layer by accelerating the caustic corrosion, from which hydrogen atoms diffused into the alloy forming cavities or micro-voids at the grain boundaries. Furthermore, high temperature creep promoted the evolution of the cavities only inside the tube where there were tensile residual stresses. Consequently, a combination of hydrogen embrittlement and thermal creep initiated the cracks at the grain boundaries inside the tube, and the cracks propagated at the grain boundaries along the axial direction exhibiting an intergranular feature on the inside. Then, it gradually propagated toward the outside, finally exhibiting a transgranular fracture mode on the outside.

The paper considers the influence of the heat carrier temperature variation in supply and return pipelines on the efficiency of the gas tube hot water boiler operating in the heat supply system and on its surfaces temperatures. The temperature dependence graphs of the convective bundle tube wall and flame tube on the ambient temperature have been constructed. The basic calculation formulas used for the calculation as well as the temperature graph of the heat supply system operation depending on the ambient temperature and the temperature of the heat carriers are presented. The heat supply system operation modes, under which the convective bundle surfaces are subjected to the low-temperature corrosion, have been determined.