scholarly journals Analysis of oxide scale thickness and pores position of HCM12A steel in supercritical water

2021 ◽  
Vol 40 (1) ◽  
pp. 53-65
Author(s):  
Li Sun ◽  
Weiping Yan
Keyword(s):  
Diffusion Coefficient ◽  
Oxide Scale ◽  
Supercritical Water ◽  
Heating Surface ◽  
Oxidation Mechanism ◽  
Oxygen Activity ◽  
Oxide Scales ◽  
Spinel Layer ◽  
Magnetite Layer ◽  
Iron Diffusion

Abstract More attention has been paid to the exfoliation of oxide scale on high-temperature heating surface of utility boiler. The oxidation mechanism of HCM12A steel in supercritical water is proposed and the growth of oxide film is simulated. The duplex scale contains an outer magnetite layer and an inner Cr-rich spinel layer. According to the data of Backhaus and Töpfer, the diffusion coefficient values of iron in magnetite layer are discussed and the function of R V, R I {R}_{\text{I}} for oxygen activity can be used for calculation of iron diffusion coefficients in Cr-rich spinel layer. Based on Wagner’s oxidation theory, the oxidation rate constants of HCM12A are calculated at 500 and 600°C in supercritical water, compared with experimental data of the relevant literatures. The oxygen activities at the interfaces of alloy/Cr-rich spinel oxide and magnetite/supercritical water are estimated. The simulation results of weight gain are matched with the test data. The iron diffusion mechanisms inside the magnetite layer and the Cr-rich spinel layer are analyzed. The iron diffusion coefficient at the interface of Cr-rich spinel/magnetite is discontinuous, while the oxygen activity is continuous in the whole double layer. The thickness of oxide scale on inner tube walls of the final superheater coils (T91) of a 600 MW supercritical boiler is calculated by using the calculation method provided by the paper. The modeling results, the measured data, and the calculation results by the method are compared. Accurate calculation of the thickness of the inner and outer oxide scales can provide a necessary basis for predicting the stress and exfoliation of oxide scales.

scholarly journals Estimation of Oxidation Kinetics and Oxide Scale Void Position of Ferritic-Martensitic Steels in Supercritical Water

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Li Sun ◽  
Weiping Yan
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Oxide Scale ◽  
Supercritical Water ◽  
Oxidation Kinetics ◽  
Ternary Phase Diagram ◽  
Measurement Data ◽  
Oxide Scales ◽  
Martensitic Steels ◽  
Iron Diffusion

Exfoliation of oxide scales from high-temperature heating surfaces of power boilers threatened the safety of supercritical power generating units. According to available space model, the oxidation kinetics of two ferritic-martensitic steels are developed to predict in supercritical water at 400°C, 500°C, and 600°C. The iron diffusion coefficients in magnetite and Fe-Cr spinel are extrapolated from studies of Backhaus and Töpfer. According to Fe-Cr-O ternary phase diagram, oxygen partial pressure at the steel/Fe-Cr spinel oxide interface is determined. The oxygen partial pressure at the magnetite/supercritical water interface meets the equivalent oxygen partial pressure when system equilibrium has been attained. The relative error between calculated values and experimental values is analyzed and the reasons of error are suggested. The research results show that the results of simulation at 600°C are approximately close to experimental results. The iron diffusion coefficient is discontinuous in the duplex scale of two ferritic-martensitic steels. The simulation results of thicknesses of the oxide scale on tubes (T91) of final superheater of a 600 MW supercritical boiler are compared with field measurement data and calculation results by Adrian’s method. The calculated void positions of oxide scales are in good agreement with a cross-sectional SEM image of the oxide layers.

scholarly journals Microstructures of SiO2 Scales Formed on MoSi2

2006 ◽  
Vol 522-523 ◽  
pp. 595-602 ◽  
Author(s):  
Kazuya Kurokawa ◽  
Daichi Goto ◽  
Jyunichi Kuchino ◽  
Akira Yamauchi ◽  
Tamaki Shibayama ◽  
...  
Keyword(s):  
Growth Rate ◽  
Diffusion Coefficient ◽  
Oxide Scale ◽  
Oxidation Rate ◽  
Diffusion Mechanism ◽  
Lattice Diffusion ◽  
Oxide Scales ◽  
Amorphous Sio2 ◽  
O2 Diffusion ◽  
Diffusion Coefficient Of Oxygen

The microstructures of oxide scales formed on MoSi2 at medium-high temperatures in air were observed by TEM. Based on the observation, relationships between oxidation temperature and formation of MoO3 and crystallization of amorphous SiO2 scales were investigated. At 1273 K and 1373 K, the oxide scales had a structure consisting of amorphous SiO2 with small amounts of fine MoO3 particles. The oxide scales at 1573 K and 1773 K had a structure consisting of amorphous and crystalline SiO2. Growth rate of the oxide scale formed at 1773 K appreciably increased due to crystallization of amorphous SiO2. It was thought that the increase in the oxidation rate at 1773 K was caused by a change in the diffusion mechanism from O2 diffusion to lattice diffusion of O2- through SiO2. In addition, the diffusion coefficient of oxygen was estimated from the growth rate of SiO2 scale.

Effect of Perovskite Coating on Oxide Scale Growth on Fe-22Cr

2006 ◽  
Vol 258-260 ◽  
pp. 372-377
Author(s):  
Åase Persson ◽  
Peter V. Hendriksen ◽  
Lars Mikkelsen ◽  
Marcel A.J. Somers
Keyword(s):  
Growth Rate ◽  
Oxide Scale ◽  
Oxidation Rate ◽  
Oxidation Mechanism ◽  
Scale Growth ◽  
Spinel Layer ◽  
Oxide Layers

A coating consisting of La0.85Sr0.15MnO3 (LSM) was deposited onto two Fe 22 wt % Cr alloys Crofer 22APU and Sandvik 1C44Mo20. The evolution of the oxide layers developing underneath the coatings during oxidation was investigated. The effect of the LSM coating on oxidation rate and microstructure of the oxide scale was investigated, and possible effects on the overall oxidation mechanism are discussed. It was found that the growth rate for coated Crofer 22APU was decreased by a factor of 3 in comparison with the uncoated samples, and the thickness of the chromia layer in the scales decreased in favor for a (Mn,Cr)-spinel layer.

scholarly journals Steam Oxidation of Austenitic Heat-Resistant Steels TP347H and TP347HFG at 650–800 °C

Materials ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 577 ◽  
Author(s):  
Zhiyuan Liang ◽  
Qinxin Zhao
Keyword(s):  
Oxide Scale ◽  
Steam Oxidation ◽  
Oxidation Products ◽  
Oxide Scales ◽  
Metallic Ions ◽  
Breakaway Oxidation ◽  
Outward Diffusion ◽  
X Ray ◽  
Heat Resistant ◽  
Heat Resistant Steels

Steam oxidation of austenitic heat-resistant steels TP347H and TP347HFG at 650–800 °C was investigated. Comprehensive micro-characterization technologies containing Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) were employed to observe and analyze the oxidation products. Results show that breakaway oxidation behaviors were observed on TP347H at 700 °C and 800 °C. The oxidation kinetics of TP347HFG at 650–800 °C followed a parabolic law. The oxide scales formed on TP347HFG were composed of MnCr2O4 and Cr2O3. A thin and protective Cr-rich oxide scale was replaced by Fe2O3 nodules due to the insufficient outward migration of metallic ions, including Cr and Mn at the subsurface of coarse-grain TP347H. Smaller grain of TP347HFG promoted the formation of the compact Cr-rich oxide scales. At higher temperatures, the incubation period for breakaway oxidation of the Cr-rich oxide scale was much shorter because of quick evaporation of the Cr2O3 oxide scale and the slower outward diffusion of metallic ions via the grain boundaries.

A study of the mechanism of corrosion of some ferritic steels in high-pressure carbon dioxide with the aid of oxygen-18 as a tracer - III. Fe-9% Cr-1 % Mo-0.26 % Si

1989 ◽  
Vol 422 (1863) ◽  
pp. 279-288 ◽  
Keyword(s):  
Carbon Dioxide ◽  
High Pressure ◽  
Charged Particle ◽  
Oxidation Mechanism ◽  
Ferritic Steels ◽  
Oxide Scales ◽  
Substantial Growth ◽  
Nuclear Techniques ◽  
Duplex Scale ◽  
Multilayered Scale

The oxidation mechanism of a commercial Fe-9% Cr steel in high-pressure (4.1 MPa) carbon dioxide at 913 K have been investigated with the aid of charged-particle nuclear techniques and 18 O as a tracer. Duplex and multilayered oxide‒scales were examined. Both types of scale grew at the oxide‒gas interface. Substantial growth occurred in the inner half of the inner layer on the specimen with the duplex scale; very little growth occurred within the inner layer of the multilayered scale. A possible oxidation sequence which could account for the 18 O distributions is proposed.

Non-catalytic supercritical water partial oxidation mechanism of coal

2020 ◽  
Vol 45 (41) ◽  
pp. 21178-21185
Author(s):  
Zhiwei Ge ◽  
Shenghui Guo ◽  
Changyifan Ren ◽  
Yu Wang ◽  
Liejin Guo ◽  
...  
Keyword(s):  
Partial Oxidation ◽  
Supercritical Water ◽  
Oxidation Mechanism

Predictions and Analyses on the Growth Behavior of Oxide Scales Formed on Ferritic–Martensitic in Supercritical Water

2019 ◽  
Vol 92 (1-2) ◽  
pp. 27-48 ◽  
Author(s):  
Yanhui Li ◽  
Tongtong Xu ◽  
Shuzhong Wang ◽  
Jie Yang ◽  
Balazs Fekete ◽  
...  
Keyword(s):  
Supercritical Water ◽  
Growth Behavior ◽  
Oxide Scales

Study on Formation and Exfoliation Mechanism of Alloy TP347H’s Oxide Scale in Supercritical Boiler

2011 ◽  
Vol 295-297 ◽  
pp. 392-396
Author(s):  
Jin Xi Zheng ◽  
Zhi Hu Ai ◽  
Ding Ping Liu
Keyword(s):  
Oxide Scale ◽  
Large Scale ◽  
Influence Factor ◽  
Energy Dispersive Spectrometer ◽  
Heating Surface ◽  
Structural Features ◽  
X Ray ◽  
Constituent Elements ◽  
Temperature Heating ◽  
High Temperature Heating

The paper addresses the assessment of the steam-side oxidation behavior of alloy TP347H tubes in supercritical boilers.The high temperature heating surface of supercritical boiler can easily form the oxide scale on the inside surfaces of steam tubes after a period of operation. When accumulated to a certain amount, the oxide scale would exfoliate. It could influence the actuating medium flowing and heat transferring, cause overheating or even the explosion of heating surface. The oxide scale sampled on heat-absorbing surface of alloy TP347H tubes was examined. The oxide exfoliation sampled was studied experimentally by energy dispersive spectrometer and the X-ray diffractometer. The constituent elements and structural features of oxide scale in TP347H tubes were emphatically analyzed. The mechanism of steam-side oxidation and scale exfoliation in the TP347H tubes, as well as its influence factor, were described. It is found that the temperature is one of the most important influences. The measures that controlled the oxide exfoliation on a large scale were brought forward so as to provide a scientific guidance for reducing the oxide scale formation and avoiding tube bursting for over-temperature.

Oxidation Kinetics of Nitrogen Doped TiO2-δ Thin Films: Analysis on the Basis of Oxygen Activity Dependence of the Chemical Diffusion Coefficient

2018 ◽  
Vol 383 ◽  
pp. 147-152
Author(s):  
Misha Sinder ◽  
Jian Min Shi ◽  
Klaus Dieter Becker
Keyword(s):  
Thin Films ◽  
Diffusion Coefficient ◽  
Electron Concentration ◽  
Chemical Diffusion ◽  
Oxygen Activity ◽  
Chemical Diffusion Coefficient ◽  
Recombination Reaction ◽  
Nitrogen Doped ◽  
Pressure Profiles ◽  
Concentration Step

The model explaining the occurrence of the electron concentration step front during oxidation of nitrogen-doped TiO2-δ thin films is presented. This model is based on ambipolar chemical diffusion coefficient analysis, for which immobile and uniformly distributed nitrogen component is assumed. The diffusion species and oxygen activity (pressure) profiles are obtained by numerical and approximate analytical simulation of the chemical diffusion. The profiles indicate the presence of two separate singularities: the electron concentration step front, and the electron-hole recombination reaction front. The electron concentration step front relates to the singularity of the ambipolar diffusion of three types of charged species with essentially different diffusion coefficients.

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