Long-term High-temperature Operation Research Articles

The design of the insulation layer and energy consumption optimization of the injection mould for the motor commutator

The injection molding of the motor commutator requires a long-term high-temperature operation, which poses a problem of high energy consumption. The heating zone is located behind the mold, and there is thermal radiation and convection during heating, resulting in uneven temperature distribution. To solve the above problems, an automatic lifting and insulation mechanism is proposed. An insulation frame is built with an aerogel insulation layer inside. It is connected up to the upper table of the machine, moving up and down during processing, and connected down to the crank slider mechanism. Simulation software analyzes its insulation and temperature distribution and, through experimental verification, compares the temperature distribution and energy consumption of injection molds before and after the installation of insulation mechanisms. The experimental and simulation results show that using the automatic lifting insulation layer design scheme can effectively reduce energy consumption, improve temperature distribution unevenness, and increase the yield rate.

Perovskite evolution on La modified Mn1.5Co1.5O4 spinel through thermal ageing with enhanced oxidation activity: Is sintering always an issue?

Non-precious metal oxides have great potential in catalytic deep oxidation of emitted hydrocarbons to help address various environmental pollution concerns. However, sintering issue is a stumbling block in practical application upon long-term high-temperature operation or thermal shock experience. Herein, La was applied to modify Mn1.5Co1.5O4 spinel to get a highly active oxidation catalyst with exceptional stability against high-temperature thermal ageing treatment. With thermal ageing at 750 °C for 100 h, the La modified Mn–Co composite reached 90 % conversion in toluene oxidation at 265 °C under the high WHSV of 120,000 mL g−1 h−1, while this value increased to 312 °C over blank Mn–Co spinel. The addition of La not only inhibited the growth of spinel nanocrystals, but also brought about perovskite formation through sintering, generating perovskite-spinel interfaces, thus enhancing both activity and stability. Meanwhile, the La modified Mn–Co spinel exhibited superior performance in presence of water or sulfur dioxide after thermal ageing treatment. This work offers a versatile strategy to design anti-sintering and active oxidation nanocatalysts based on non-precious metal oxides for industrial applications.

Changes of steel grade 10Cr2Mo properties as a result of structural and phase transformations caused by long-term high-temperature operation

Changes of steel grade 10Cr2Mo properties as a result of structural and phase transformations caused by long-term high-temperature operation

A limiting current oxygen sensor with (CuO)0.1(8YSZ)0.9 dense diffusion barrier

In this paper, (CuO)x(8YSZ)1-x (0 ≤ x ≤ 0.3) is prepared by using a co-precipitation method. Its electrical conductivity increases to a maximum at (CuO)0.1(8YSZ)0.9, and then decreases with increasing CuO doping content. An oxygen sensor is fabricated by Pt paste method based on 8YSZ (8 mol% Y2O3 stabilized ZrO2) solid electrolyte and (CuO)0.1(8YSZ)0.9 dense diffusion barrier for the first time. A limiting current of the sensor is reached under different conditions, such as temperature (T) of 720–870 °C, oxygen concentration (x(O2)) of 0–4%, carbon dioxide concentration (x(CO2)) of 0–100%, water vapor pressure (p(H2O)) of 280.66–2268.63 Pa, and testing time of 120 h. The oxygen sensor exhibits excellent sensing performances, its single selectivity to oxygen and resistance to interference from other gases. Moreover, the performances of the oxygen sensor do not decay and remain well under long-term high temperature operation.

Predicting the state of heat-resistant steel of a steam pipeline at a TPP taking into account changes in its strength due to operational damage

The microstructure of heat-resistant 15Kh1M1F steel is analysed in the initial state and after long-term operation on the main steam pipelines of TPPs. According to the criteria adopted in fracture mechanics, the low volumetric content of fine carbides, which did not exceed 0.5% in the structure of the analysed steel in the initial state, does not significantly affect its strength. However, as a result of long-term high-temperature operation, a redistribution of carbon and alloying elements occurred in its structure with the precipitation and coagulation of carbides along the grain boundaries. Large carbides concentrated along the grain boundaries have a low cohesion with the matrix, which promotes the formation of pores along their interfaces. As a result, the cohesion of adjacent grains decreases, which contributes to the formation of a system of intergranular microcracks. Merging, they form a macrocrack, which has a significant effect on the strength of the material.A mathematical model is proposed for predicting changes in the ultimate strength of steel, based on the well-known solution of the problem with tension of a body with a periodic system of collinear cracks. The relationship between the intensity of tensile forces, the distance between the cracks, their size and the size of the pre-fracture zones in the vicinity of operational defects is found. The beginning of the merging of the pre-fracture zones at the tips of the nearest defects was taken as the condition for material destruction.A dependence has been obtained that makes it possible to make predictive estimates of a decrease in the ultimate strength of long-term operation of steel on steam pipelines of different units, due to its additional damage under the influence of shutdown numbers of TPP units corresponding to this steel. To do this, it is only necessary to calculate the fraction of the steel resource loss according to normalized technological indicators, such as the operation lifetime and the number of shutdowns of the units.

Features of Acoustic Emission in Tensile Testing of Dissimilar Welded Joints of Pearlitic and Austenitic Steels

This paper presents a study of acoustic emission (AE) during the deformation of dissimilar welded joints of austenitic steel to pearlitic steel. One of the specific problems in these welded joints is the presence of decarburized and carbide diffusion interlayers, which intensively increase in width during long-term high-temperature operation. The presence of wide interlayers negatively affects the mechanical properties of welded joints. Moreover, welded defects are difficult to diagnose in welded joints containing interlayers: due to the high structural heterogeneity, interlayers create structural noises that can hinder the detection of defects such as cracks, pores, or a lack of penetration. The AE method may become a complex decision for diagnosing dissimilar welded joints due to applicability to the testing of heterogenic materials with a complex microstructure. Specimens cut from dissimilar welded joints of austenitic steel to pearlitic steel were tested by tension to rupture, with parallel AE data registration. According to the research results, the characteristic features of the AE were revealed for specimens containing defects in the form of lack of penetration as well as for specimens with diffusion interlayers. The results obtained show that the AE method can be used to test both typical welding defects and diffusion interlayers in welded joints of steels of different structural classes.

Ultrahigh temperature platinum microheater encapsulated by reduced-TiO2 barrier layer

Thermal stability and adhesion of the Pt/barrier interface were investigated herein. Reduced-TiO2, or TiO2-δ, was found to offer stronger adhesion and greater thermal stability as a barrier layer for Pt than that of TiN and stoichiometric TiO2. It enables a long-term high-temperature operation. No voids or peeling was seen after annealing at a temperature of 700 °C in a stacked layer of Pt/ TiO2-δ; whereas, voids and peeling inevitably appeared in Pt layers on TiN and TiO2, respectively. A microhotplate composed of a Pt/TiO2-δ microheater was confirmed to perform at 800 °C at a heating power of 120 mW. The heating response time was below 20 ms between 150 °C and 800 °C. Ten million cycles of temperature modulation between room temperature and 550 °C did not cause any performance deterioration.

On the creep fatigue and creep rupture behaviours of 9–12% Cr steam turbine rotor

This paper presents the study of creep-fatigue interaction damage and creep rupture limit for 9–12% Cr steam turbine rotor under coupled cyclic thermal-mechanical loadings that alter in phase and out of phase. The investigation is implemented using the Linear Matching Method (LMM) and based on the newly developed creep-fatigue and creep rupture evaluation procedures. Latest experimental creep data of FB2 which belongs to 9–12% Cr heat-resistant steel family is employed to calculate creep-related damage and creep rupture bearing capacity of steam turbine rotor. Various factors that affect creep and fatigue damage of steam turbine rotor are analyzed and discussed, including dwell period and rotating speed of rotor. From the parametric studies, the damage locations and cycles to failure induced by creep and fatigue mechanism are presented respectively. Moreover, through creep rupture analyses for varying desired fracture time, the novel creep rupture curves under multi-type double-cyclic-loading conditions are given and further compared with cyclic plasticity failure curve. These surrogate-model analyses offer a deep understanding of structural responses of steam turbine rotor under long-term high temperature operation and provide critical loading conditions to be referenced for smooth running.

Effect of long-term thermal aging in heat exchange equipment of fast neutron switchgears on the structure and properties of austenitic chromium-nickel steel

The influence of long-term operation at 515 °C on structure and properties of 09Cr18Ni9 steel was investigated. Structure and phase composition were obtained using optical and scanning electron microscopy. The phase composition of the steel in equilibrium state was determined by thermodynamic modeling in the software package Fact-Sage. As a result of the study, it was found that during the operation at 515 °C with a duration of 195,000 h, the structure changes occurred in the 09Cr18Ni9 steel with the formation of secondary phases, initiated by the release of elements with limited solubility from the supersaturated solid solution. The following secondary precipitates in structure of the solid solution of austenite presented: Cr23C6 chromium carbide, ferrite (a), G-phase. Based on comparison of the thermodynamic modeling results and on experimental determination of the phase composition, it was established that the steel structure is in a state close to equilibrium. The mechanism of structural transformations course and sequence of the secondary phases’ formation were revealed and described. At the initial stage, chromium carbide is formed, then a-ferrite is formed near the carbides, and then G-phase is formed. Results of the tests for impact strength and static elongation have shown that the change in phase composition in process of thermal aging leads to embrittlement of the steel - a reduction in ductility and impact energy. Fractografic studies of fracture surfaces of the samples have shown that the decrease in plasticity during long-term high-temperature operation is associated with softening of the grain body and strengthening of the boundaries due to secondary precipitations of the carbide phase. As a result of this process, plastic deformation is localized in the weakened volume of the body of grain surrounded by strong boundaries. The structure evolution during prolonged heat aging has the greatest effect on impact strength. At the same time, the change in ultimate and yield stress is insignificant. The main contribution to the change in mechanical characteristics of steel is made by the secondary precipitates of the carbide phase.

In operando optical study of active three phase boundary of nickel-yttria stabilized zirconia solid-oxide fuel cell anode under polarization

Degradation of solid oxide fuel cell (SOFC) anode always takes place during long-term high temperature operation because of the decrease in three phase boundary (TPB) density and loss of nickel (Ni) network percolation due to Ni coarsening. In the present study, for the first time, an in operando observation technology using optical laser microscope is developed to demonstrate the real-time local morphological change of Ni at active TPB under polarization conditions. The local morphological change, which is determined by the competition between the mechanisms of enhanced Ni wettability on yttria-stabilized zirconia (YSZ) surface and thin Ni-film break up caused by Ni coarsening are observed. In operando observation reveals the reason of rapid performance degradation of SOFC anode under sever operation conditions. It is expected that the in operando observation of Ni morphological change can largely enrich our understanding of the SOFC anode microstructure change, which may further supply precious opportunities to investigate sever degradation mechanisms.

Heat transfer analysis of a new volumetric based receiver for parabolic trough solar collector

Abstract Effective use of selective absorbing coating in surface based receivers and nanofluids in volumetric based receivers for better thermal performance have been confirmed in previous studies. However, in practical application, these receivers suffered from the problem of performance degradation after long-term high-temperature operation, and they were high-cost. This study proposed a novel kind of parabolic trough receiver by locating the absorber tube inside heat transfer fluid (HTF) in a twin glass tube, and developed its mathematical heat transfer model. Based on this model, the novel receiver was verified to be desirable when the inlet temperature of HTF was lower than 150 °C (with an efficiency sacrifice within 4%), and particularly in the range of 100–120 °C (with an efficiency sacrifice within 1.5%). Strategies including replacing the selective absorbing coating with non-selective absorbing coating, lowering the velocity of outer HTF and lowering the emissivity of the inner glass tube were investigated and verified to be effective in specific conditions.

Reliability Investigations of AlGaN/GaN HEMTs Based on On-State Electroluminescence Characterization

In this paper, we investigated ON-state electroluminescence (EL) characteristics in fresh GaN-based HEMTs under different ON-state bias conditions. It demonstrated that: 1) the intensity of the ON-state EL emitted by the GaN-based HEMTs with relatively high V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> > 10 V) monotonically increased as the gate voltage increased; and 2) the distribution of the intensity of the ON-state EL was uniform along the gate and across the device before stress tests. The degradation process and mechanisms of the devices in the high temperature operation (HTO) stress were also analyzed based on the ON-state EL characterization, the electrical measurement, and failure analysis. It demonstrated the following. First, the ON-state EL distribution of the device after step HTO (S-HTO) stress tests was no longer uniform along one of the fingers, which indicated that the degradation was related to this finger. This hypothesis was confirmed by the SEM observation after the deprocess of the gate metal and the SiN passivation layer. Second, a new degradation mechanism of AlGaN/GaN HEMTs that caused the abrupt degradation in the S-HTO stress was identified and related to the emergent, localized, and jagged crack under the gate metal. Third, there was no abrupt degradation in the long-term HTO (LT-HTO) stress test. However, the ON-state EL intensity of the inner fingers in the device after the LT-HTO stress test decreased more than that of the outer fingers, which meant that the degradation of the inner fingers was faster than that of the outer fingers as a result of the higher temperature caused by self-heating in the inner region of the device. Finally, the gradual degradation in the LT-HTO stress test was ascribed to the gradual formation of structural damage along the drain side of the whole gate edge, which was confirmed by the SEM observation.

Research on Substation Equipment Temperature Monitoring Technology

with the substation construction and retrofit, gradually achieve the unattended substation operation, long-term high temperature operation is the main cause of equipment wear and tear, fault, in view of the continuously monitor equipment operation temperature, helps to discover the hidden trouble of equipment operation, master the equipment running status, improve the operating life of equipment. Temperature measuring technology as the main technical means, through continuous improvement to upgrade, there are so many ways to achieve, but the lack of standards and specifications. Through the comparison and analysis of the principle of the existing equipment temperature monitoring technology, concludes the key points of equipment temperature measurement technology, discusses the development trend of substation equipment temperature measurement technology, formation of substation equipment should have the characteristics of temperature monitoring technology. In substation operations management and equipment maintenance as the goal, combined with the Internet of things, the sensing technology, the realization of intelligent substation temperature measuring technology application.

Establishment of control technology of the HTTR and future test plan

The high-temperature engineering test reactor (HTTR) has carried out several demonstration tests to obtain basic data for the design of a future high-temperature gas-cooled reactor (HTGR). In addition, for commercial HTGRs, it also should be demonstrated that the HTGR system can supply stable heat to heat utilization system for the long term. To demonstrate the capability of HTGRs of stable heat supply, the operational experience of the HTTR would be useful. The control characteristics of the HTTR are evaluated by the result of the long-term high-temperature operation performed in 2010. As the result, it is confirmed that control technology of the HTTR is enough to achieve the control response with reasonable damped characteristics and the stable normal operation. In addition, a future possibility of the thermal-load fluctuation and lost test is examined. The data would contribute design of heat utilization system because heat utilization system is required to be a non-safety system. For the future HTGR system design, the requirement, method and result of determination of control constants are discussed. The behavior of control system is described with the characteristics of the HTGR during the past test using HTTR. In addition, this paper proposes a future test plan for demonstration of the reactor stability and control technology against thermal load fluctuation for future HTGR with a heat utilization system design.

Investigation of chemical characteristics of primary helium gas coolant of HTTR (high temperature engineering test reactor)

The technical basis of helium gas purification control for HTGRs was established by verifying the design of the Primary Helium Purification System (PHPS) of the HTTR by showing that the measured concentrations of impurities of the primary helium coolant were restricted below the criteria of control to protect the graphite oxidation, and that the carburization atmosphere was maintained to keep intact of metallic high temperature components, in the 30-day continuous operation and the 50-day long-term high temperature operation. The analytical model, which was newly established by improving the conventional method that predicted the impurity concentrations conservatively higher than the measured values, predicted the composition of the impurities such as H2, CO, H2O and CO2, which is determined by the temperature dependency of release of impurities during the rated power operation adequately. In contrast, it was revealed that the measured concentration of H2O remarkably decreased while the concentration of CO increased in the primary helium coolant in the long-term high temperature operation.

ChemInform Abstract: Ceramic Integration Technologies for Solid Oxide Fuel Cells

AbstractReview: 52 refs.

Diffusion aluminide coatings for internal surface of rhenium- and rhenium-ruthenium-containing single-crystal superalloys turbine blades: Part I

Process of formation rhenium or refractory carbides based diffusion barrier layer (coating) on internal surface of rhenium- and rhenium-ruthenium-containing single-crystal high-temperature alloys (superalloy) turbine blades, prior to diffusion aluminide coating deposition, is studied. It is shown that diffusion barrier layer is preventing deleterious secondary reaction zone formation under aluminide coating during long-term high-temperature operation. The kinetics of powder carburizing process of rhenium- and rhenium-ruthenium-containing high-temperature alloys is investigated, and conditions for carburizing these alloys are determined. The phase composition of the surface layer after carburizing is studied, and the effect of the fractional composition of a carbon-based powder mixture on the carburizing rate is determined.

Long-term high-temperature operation of the HTTR

The high temperature engineering test reactor (HTTR) constructed at the Oarai Research and Development Center of the Japan Atomic Energy Agency (JAEA) is the first high-temperature gas-cooled reactor (HTGR) in Japan. The HTTR is a graphite-moderated and helium-gas-cooled reactor. The reactor thermal power is 30MW, and the reactor maximum outlet coolant temperature is 850°C in rated operation mode and 950°C in high-temperature test operation mode. The main objectives of the HTTR are to establish and develop HTGR technology and to demonstrate process heat application.The HTTR was operated for 30days in rated operation mode and 50days in high-temperature operation mode to obtain various characteristic data for HTGRs. The main test results are as follows:(1)The coated fuel particles (CFPs) of the HTTR are excellent at confining the fission product and have the highest performance in the world.(2)The measured temperature of the core internals is in good agreement with the design value, which means that they will maintain their structural integrity.(3)The intermediate heat exchanger maintains excellent heat transfer performance from the beginning of operation.In addition, the following two issues were validated using the HTTR burnup data: (1) the effectiveness of rod-type burnable poisons at reactivity control in the HTTR and (2) the whole core burnup calculation method for the nuclear characteristics of the HTTR.

Composite materials with an intermetallic matrix based on nickel and titanium monoaluminides hardened by oxide particles or fibers

Hardening phase/intermetallic matrix pairs are chosen for composite materials (CMs) intended for long-term high-temperature operation. These materials must have high and stable mechanical properties during a long time at high temperatures and loads. The compatibility of the physicochemical and mechanical properties of CM components is estimated to choose hardening phase/intermetallic matrix pairs in which the matrix is represented by an alloy based on NiAl or TiAl monoaluminide and the hardening phase is a refractory thermodynamically stable oxide of a Group III transition metal M2O3. The following two schemes are used to perform hardening of a CM with a matrix consisting of a TiAl or NiAl alloy by the most thermodynamically stable interstitial phases, i.e., refractory oxides, at temperatures higher than the operating temperature (Top) of the IMM. The first scheme consists in creating Al2O3/TiAl CMs hardened by continuous single-crystal sapphire fibers using the impregnation of a bundle of single-crystal fibers with a matrix melt followed by directional solidification. The TiAl-based matrix in these CMs serves as a binder connecting oxide phase fibers and preventing them from fracture due to high adhesion forces between oxide fibers and the matrix and a high fiber/matrix interface strength. In the second scheme, Y2O3/NiAl CMs are produced by powder metallurgy methods, which include severe deformation by extrusion accompanied by the formation of deformation texture and subsequent recrystallization annealing. In these CMs, disperse refractory oxide particles stabilize grain boundaries in a recrystallized matrix material and lead to the formation of directional structures with coarse elongated grains and a low fraction of transverse boundaries. Al2O3/TiAl CMs containing 20–25 vol % hardening single-crystal sapphire Al2O3 fibers can operate at temperatures of 1000–1050°C (∼0.7Tm of matrix), which is 250–300°C higher than the maximum values of Top of a TiAl-based matrix and 400-450°C higher than the maximum values of Top of a Ti-based matrix. An Y2O3/NiAl composite with a directionally recrystallized structure of a NiAl-based matrix hardened by 2.5 vol % Y{ia2}O3 particles can be recommended for operation at temperatures of 1400–1500°C ((0.8–0.9)Tm of matrix), which are higher by 100–400°C than not only Top but also Tm of Ni superalloys.

Development of high temperature gas-cooled reactor (HTGR) fuel in Japan

This paper describes experiences and present status of research and development works for the high temperature gas-cooled reactor (HTGR) fuel in Japan. Recently, Very High Temperature Reactor (VHTR) is evaluated highly worldwide, and is a principal candidate for the Generation IV reactor systems. In Japan, HTGR fuel fabrication technologies have been developed through the High Temperature Engineering Test Reactor (HTTR) project in Japan Atomic Energy Agency since 1960’s. In total about 2 tons of uranium of the HTTR fuel has been fabricated successfully and its excellent quality has been confirmed through the long-term high temperature operation. Based on the HTTR fuel technologies, SiC TRISO fuel has been newly developed for burnup extension targeted VHTR. For ZrC-TRISO coated fuel as an advanced fuel designs, R&Ds for fabrication and inspection have been carried out in JAEA. The irradiation with the Japanese uniform stoichiometric ZrC coating has been completed in the cooperation with Oak Ridge National Laboratory of the United States.