scholarly journals Effect of Shot Peening on the Evolution of Scale on T91 Steel Exposed to Steam

2021 ◽  
Vol 11 (19) ◽  
pp. 8831
Author(s):  
Liming Xu ◽  
Yinsheng He ◽  
Yeonkwan Kang ◽  
Keesam Shin
Keyword(s):  
Oxide Scale ◽  
Shot Peening ◽  
Power Plants ◽  
Hardness Test ◽  
Oxide Scales ◽  
Effective Solution ◽  
Micro Cracks ◽  
Topmost Layer ◽  
Microscopic Techniques ◽  
Vickers Hardness Test

Shot peening can be an effective solution for the prevention or retardation of scale formation, and subsequent exfoliation, upon exposure of the inner tube to steam in coal-fired power plants. In this study, specimens of T91 tubes were shot peened and then exposed to 1-bar steam for 100–1000 h at 650 °C, and were then analyzed using Vickers hardness test and microscopic techniques OM, SEM, TEM, etc. The analysis indicates that the oxide scales are typically Fe2O3 on the topmost layer, Fe3O4 below, and a FeCr2O4 spinel on the bottom in both shot peening treated and untreated specimens. However, the oxide scale thicknesses of shot peened specimens are thinner, indicating that shot peened specimens have better oxidation resistance. In addition, numerous defects, such as voids and micro-cracks, were found in the untreated specimens, which are believed to cause exfoliation of the uppermost Fe2O3 layers of the specimens exposed to steam for 800 and 1000 h. By contrast, the shot peened specimens maintained a dense contact oxide scale with fewer defects.

Thermal Stress Development in Steam-Side Oxide Scales in High Temperature Components of Boilers under Thermal Shock

2014 ◽  
Vol 997 ◽  
pp. 692-695
Author(s):  
Cai Xia Bian ◽  
Ke Yi Zhou ◽  
Zheng Lin Zhu ◽  
Xiao Long Bi
Keyword(s):  
High Temperature ◽  
Oxide Scale ◽  
Thermal Shock ◽  
Power Plants ◽  
Thermal Power ◽  
Oxide Scales ◽  
Element Analysis ◽  
Boiler Tubes ◽  
High Temperature Components ◽  
Scale Failure

Failure of steam-side oxide scales in high temperature components of boilers such as superheater and reheater tubes has significant effect on the safety of thermal power plants. Finite element analysis is carried out to investigate the failure issues of steam-side oxide scales in boiler tubes during thermal shock processes. The effects of different steam temperature variation durations on oxide scale failure issues have been analyzed. According to the results, appropriately lengthening variation duration can contribute to relieving oxide scale failure issues, and are subsequently proposed.

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 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.

scholarly journals The effect of various Co contents on the microstructure and properties of Ti(C,N)-TiB2-Co cermets prepared in situ via reactive hot pressing

2020 ◽  
Vol 12 (5) ◽  
pp. 168781402092571
Author(s):  
Xianrui Zhao ◽  
Ze Yu ◽  
Dunwen Zuo ◽  
Qintao Li ◽  
Mengxian Zhang ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Relative Density ◽  
Vickers Hardness ◽  
Hot Pressing ◽  
Hardness Test ◽  
Reactive Hot Pressing ◽  
Compacting Pressure ◽  
Vickers Hardness Test ◽  
Scanning Electron

Ti(C,N)-TiB2-Co cermets were in situ synthesized, via reactive hot pressing from the Co-Ti-C-BN system, with a Co content ranging from 6 to 22 wt%. The microstructure, relative density, hardness, and fracture toughness of the sintered compacts was investigated by light microscopy, scanning electron microscopy, ceramic densitometry, and Vickers hardness test. The investigations indicate that during hot pressing (compacting pressure = 30 MPa), when the Co content is 14–22 wt%, the metal binder is extruded. Co and Ti are included in the extrudate, breaking the original ratio and deteriorating the properties of the sintered products. As the Co content increases from 6 wt% to 12 wt%, the porosity increases, and the relative density increases from 97.2% to 99.5%. The fracture toughness increases from 6.1 to 6.8 MPa m1/2. The Vickers hardness first increases from 1897 HV10 to the maximum 1960 HV10 and then decreases slightly to 1945 HV10.

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