scholarly journals Coupling effect of temperature and Cr content on the steam oxidation of Ni-Fe-Cr alloys

2021 ◽  
Author(s):  
Huihui Zhang ◽  
Lezheng Huang ◽  
Zhen Yang ◽  
Jie Chen ◽  
Yanjia Liu ◽  
...  
Keyword(s):  
Power Plants ◽  
Coupling Effect ◽  
Degradation Mechanism ◽  
Oxidation Mechanism ◽  
Steam Oxidation ◽  
Effect Of Temperature ◽  
Scale Morphology ◽  
Cr Content ◽  
Oxide Phases ◽  
High Temperature Steam

Abstract Excellent resistance to steam oxidation is a key required property for heat-resistant alloys used in next-generation fossil power plants. In order to clarify the degradation mechanism of Ni-Fe-Cr alloys in high temperature steam, four kinds of Ni-Fe-Cr model alloys with various Cr content were prepared and their long-term steam oxidation were investigated at 650 oC and 700 oC. The microstructure and composition of oxide scales were characterized by SEM equipped with EDS, and the oxide phases were identified by XRD. The results showed significant dependence of temperature and Cr content in alloys on the oxidation kinetics, cross-section morphology and elemental section-distribution. For Ni-Fe-Cr alloys with low Cr contents (12~16 wt.%), the increase of temperature made the oxide scale change from breakaway scale morphology (nodule-crater microstructure with external exfoliation) to protective scale morphology (uniform layer and internal oxidation). For Ni-Fe-Cr alloy with 18wt.% Cr, the effect of temperature was greatly reduced. The oxidation mechanism was discussed from the perspectives of selective oxidation and the effect of alloying elements.

Evaluation of Si Coating on Ferritic Steels by CVD-FBR Technology in Steam Oxidation

2009 ◽  
Vol 289-292 ◽  
pp. 413-420 ◽  
Author(s):  
F.J. Bolívar ◽  
L. Sánchez ◽  
M.P. Hierro ◽  
F.J. Pérez
Keyword(s):  
Power Plants ◽  
Protective Coatings ◽  
Steam Oxidation ◽  
Steam Turbines ◽  
X Ray Diffraction ◽  
Steam Power ◽  
Factors Affecting ◽  
Steam Power Plants ◽  
Temperature And Pressure ◽  
Major Factors

The development of new power generation plants firing fossil fuel is aiming at achieving higher thermal efficiencies of the energy conversion process. The major factors affecting the efficiency of the conventional steam power plants are the temperature and, to a lesser extent, the pressure of the steam entering the turbine. The increased operating temperature and pressure require new materials that have major oxidation resistance. Due to this problem, in the last years numerous studies have been conducted in order to develop new coatings to enhance the resistance of steels with chromium contents between 9 and 12% wt against steam oxidation in order to allow operation of steam turbines at 650 0C. In this study, Si protective coatings were deposited by CVD-FBR on ferritic steel P-91. These type of coatings have shown to be protective at 650 0C under steam for at least 3000 hours of laboratory steam exposure under atmospheric pressure. Morphology and composition of coatings were characterized by different techniques, such as scanning electron microscopy (SEM), electron probe microanalysis, and X-ray diffraction (XRD). The results show a substantial increase of steam oxidation protection afforded by Si coating by CVD-FBR process.

SiC MOSFET Channel Mobility Dependence on Substrate Doping and Temperature Considering High Density of Interface Traps

2007 ◽  
Vol 556-557 ◽  
pp. 835-838 ◽  
Author(s):  
Amador Pérez-Tomás ◽  
Michael R. Jennings ◽  
Philip A. Mawby ◽  
James A. Covington ◽  
Phillippe Godignon ◽  
...  
Keyword(s):  
Degradation Mechanism ◽  
Mobility Model ◽  
Effect Of Temperature ◽  
Coulomb Scattering ◽  
Interface Traps ◽  
Channel Mobility ◽  
Inversion Channel ◽  
Scattering Effects ◽  
Charge Concentration ◽  
Substrate Doping

In prior work we have proposed a mobility model for describing the mobility degradation observed in SiC MOSFET devices, suitable for being implemented into a commercial simulator, including Coulomb scattering effects at interface traps. In this paper, the effect of temperature and doping on the channel mobility has been modelled. The computation results suggest that the Coulomb scattering at charged interface traps is the dominant degradation mechanism. Simulations also show that a temperature increase implies an improvement in field-effect mobility since the inversion channel concentration increases and the trapped charge is reduced due to bandgap narrowing. In contrast, increasing the substrate impurity concentration further degrades the fieldeffect mobility since the inversion charge concentration decreases for a given gate bias. We have good agreement between the computational results and experimental mobility measurements.

Self-healing behavior of Cr-coated Zr alloy cladding in high temperature steam oxidation process

2022 ◽  
Vol 558 ◽  
pp. 153327
Author(s):  
Hai-Bin Ma ◽  
Ya-Huan Zhao ◽  
Yang Liu ◽  
Jing-Ting Zhu ◽  
Jun Yan ◽  
...  
Keyword(s):  
High Temperature ◽  
Oxidation Process ◽  
Steam Oxidation ◽  
Self Healing ◽  
High Temperature Steam ◽  
Zr Alloy

A study on accumulator analysis for the valve performance evaluation system of nuclear power plants

Kerntechnik ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. 39-44
Author(s):  
K. Ryu ◽  
T. Lee ◽  
D. Baek ◽  
J. Park ◽  
N. Kim
Keyword(s):  
Latent Heat ◽  
Temperature Difference ◽  
Evaluation System ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
High Capacity ◽  
Test System ◽  
Performance Evaluation System ◽  
High Temperature Steam

Abstract To evaluate the valves used in the nuclear power plants are working properly under the required conditions, the performance and capacity test should be performed. In the test system, the accumulator was employed to control the large amount of high pressure and high temperature steam generated in the boiler precisely. In the accumulating process, the steam is often condensed. In order to prevent condensation, it is needed to install heaters and preheat the accumulator. However, if the size of the accumulator becomes large, the installation of the heater may not be easy. Therefore, when the test is conducted, the system was preheated by the latent heat generated from the phase change. Insufficient thermal insulation may cause temperature differences and it can cause mechanical problems in the accumulator structure. If insulation is sufficient, the temperature difference is indicated by the height. As the cooled condensate moves downwards, the condensate is discharged by the drain valve control and the temperature difference of the structure can be disappeared. The results of this paper can be applied to the conceptualization of equipment that uses latent heat and for the design of high-precision steam experimental devices or the design of high-capacity steam utilization systems.

Scaling Behavior of Superheater Tube Alloys in ASME High Temperature Steam Research Tests at 1100–1500 F

1962 ◽  
Vol 84 (3) ◽  
pp. 223-257 ◽  
Author(s):  
F. Eberle ◽  
C. H. Anderson
Keyword(s):  
High Temperature ◽  
Chemical Composition ◽  
Thermal Shock ◽  
Thermal Shock Resistance ◽  
Scaling Behavior ◽  
Effect Of Temperature ◽  
Relative Resistance ◽  
Superheater Tube ◽  
Shock Resistance ◽  
High Temperature Steam

The scales formed on seven ferritic and ten austenitic types of commercial tubing presently in use and of potential future use for superheater service were examined after 6, 12, and 18 months’ exposure to air and to flowing steam of 2000 psi at temperatures of 1100, 1200, 1350, and 1500 F. The effect of temperature and time of exposure on the adherence, thermal-shock resistance, thickness, structure, and chemical composition of the scales was investigated and the relative resistance to scaling of the various alloys evaluated.

Role of grain boundary engineered microstructure on high temperature steam oxidation behaviour of Ni based superalloy alloy 617

2019 ◽  
Vol 778 ◽  
pp. 224-233 ◽  
Author(s):  
C.N. Athreya ◽  
K. Deepak ◽  
Dong-Ik Kim ◽  
B. de Boer ◽  
Sumantra Mandal ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Oxidation Behaviour ◽  
Steam Oxidation ◽  
Alloy 617 ◽  
High Temperature Steam

Strategies for Treating Weld Residual Stresses in Probabilistic Fracture Mechanics Codes

2011 ◽  
Author(s):  
Frederick W. Brust ◽  
R. E. Kurth ◽  
D. J. Shim ◽  
David Rudland
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Power Plants ◽  
Degradation Mechanism ◽  
Welding Process ◽  
Corrosion Cracking ◽  
Uncertainty Sources

Risk based treatment of degradation and fracture in nuclear power plants has emerged as an important topic in recent years. One degradation mechanism of concern is stress corrosion cracking. Stress corrosion cracking is strongly driven by the weld residual stresses (WRS) which develop in nozzles and piping from the welding process. The weld residual stresses can have a large uncertainty associated with them. This uncertainty is caused by many sources including material property variations of base and welds metal, weld sequencing, weld repairs, weld process method, and heat inputs. Moreover, often mitigation procedures are used to correct a problem in an existing plant, which also leads to uncertainty in the WRS fields. The WRS fields are often input to probabilistic codes from weld modeling analyses. Thus another source of uncertainty is represented by the accuracy of the predictions compared with a limited set of measurements. Within the framework of a probabilistic degradation and fracture mechanics code these uncertainties must all be accounted for properly. Here we summarize several possibilities for properly accounting for the uncertainty inherent in the WRS fields. Several examples are shown which illustrate ranges where these treatments work well and ranges where improvement is needed. In addition, we propose a new method for consideration. This method consists of including the uncertainty sources within the WRS fields and tabulating them within tables which are then sampled during the probabilistic realization. Several variations of this process are also discussed. Several examples illustrating the procedures are presented.

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