Corrosion Behavior Of Structural Materials Research Articles

Effect of oxide impurities on the corrosion behavior of structural materials in molten LiF-NaF-KF

The corrosion of materials in molten fluoride salts is largely influenced by the presence of impurities in the salt. Very few studies have been done on the effect of oxide impurities on the corrosion of structural alloys in molten fluoride salts. In this study, corrosion behavior of selected alloys was studied in molten FLiNaK with the addition of different oxides such as Li2O, NiO, and Cr2O3. The results show that addition of oxides can lead to significant effects on this corrosion, depending on the type and amount of oxide added and the alloy being used.

First steps toward predicting corrosion behavior of structural materials in molten salts

To address the need for physics-based models to predict corrosion behavior of materials in molten salts, the current work proposes potential methods to aid in selection of optimum materials for structural components in molten salt powered technologies. In the present work, the role of alloy thermodynamics and kinetics on governing corrosion rates of Ni-based alloys will be discussed combining experimental and computational methods. A few strategies are presented to quantify corrosion rates of Ni-based materials isothermally exposed in purified KCl-MgCl2 salts at 600 ∘ C-800 ∘ C. The influence of capsule material, potential corrosion products and role of alloy composition on the observed corrosion rates was discussed with coupled thermodynamic-kinetic models. Larger depths of corrosion attack were observed in alloy 230 specimens compared to other alloys under similar conditions was attributed to the much higher chemical activity of Cr in the alloy that results in a larger Cr chemical potential gradient.

Corrosion phenomena in sodium-potassium coolant resulting from solute interaction in multicomponent solution

The solubility of Fe, Cr, Ni, V, Mn and Mo in sodium-potassium melt has been calculated using the mathematical framework of pseudo-regular solution model. The calculation results are compared with available published experimental data on mass transfer of components of austenitic stainless steel in sodium-potassium loop under non-isothermal conditions. It is shown that the parameters of pair interaction of oxygen with transition metal can be used to predict the corrosion behavior of structural materials in sodium-potassium melt in the presence of oxygen impurity. The results of calculation of threshold concentration of oxygen of ternary oxide formation of sodium with transitional metals (Fe, Cr, Ni, V, Mn, Mo) are given in conditions when pure solid metal comes in contact with sodium-potassium melt.

Molten salt corrosion behavior of structural materials in LiCl-KCl-UCl3 by thermogravimetric study

The corrosion resistance of structural materials has been recognized as a key issue in the various unit operations such as salt purification, electrorefining, cathode processing and injection casting in the pyrochemical reprocessing of spent metallic nuclear fuels. In the present work, the corrosion behavior of the candidate materials of stainless steel (SS) 410, 2.25Cr-1Mo and 9Cr-1Mo steels was investigated in molten LiCl-KCl-UCl3 salt by thermogravimetric analysis under inert and reactive atmospheres at 500 and 600 °C, for 6 h duration. Insignificant weight gain (less than 1 mg/cm2) in the inert atmosphere and marginal weight gain (maximum 5 mg/cm2) in the reactive atmosphere were observed at both the temperatures. Chromium depletion rates and formation of Cr-rich corrosion products increased with increasing temperature of exposure in both inert and reactive atmospheres as evidenced by SEM and EDS analysis. The corrosion attack by LiCl-KCl-UCl3 molten salt, under reactive atmosphere for 6 h duration was more in the case of SS410 than 9Cr-1Mo steel followed by 2.25Cr-1Mo steel at 500 °C and the corrosion attack at 600 °C followed the order: 9Cr-1Mo steel >2.25Cr-1Mo steel > SS410. Outward diffusion of the minor alloying element, Mo was observed in 9Cr-1Mo and 2.25Cr-1Mo steels at both temperatures under reactive atmosphere. Laser Raman spectral analysis of the molten salt corrosion tested alloys under a reactive atmosphere at 500 and 600 °C for 6 h revealed the formation of unprotected Fe3O4 and α-as well as γ-Fe2O3. The results of the present study facilitate the selection of structural materials for applications in the corrosive molten salt environment at high temperatures.

Corrosion Behavior of Structural Materials for Potential Use in Nitrate Salts Based Solar Thermal Power Plants

Commercial and economic success of concentrated solar power (CSP) plants requires operating at maximum efficiency and capacity which necessitates the use of materials that are reliable at high temperatures. This study investigates the corrosion behavior of structural alloys in molten nitrate salts at three temperatures common to CSP plants. Corrosion behavior was evaluated using gravimetric and inductively-coupled plasma optical emission spectroscopy (ICP-OES) analysis. Surface oxide structure and chemistry was characterized using X-ray diffraction and Raman spectroscopy. Electrochemical behavior of candidate structural alloys Alloy 4130, austenitic stainless steel 316, and super-austenitic Incoloy 800H was evaluated using potentiodynamic polarization characteristics. Gravimetric and ICP-OES analysis indicated that Alloy 4130 exhibited the least corrosion resistance at 500°C compared to SS316 and 800H. However, at 300°C, the three alloys exhibited similar weight gain. Electrochemical evaluation of these candidate materials was observed to correlate well with the corrosion behavior observed from gravimetric and ICP-OES analysis. This study identifies that all three alloys exhibited acceptable corrosion rate in 300°C molten salt, while elevated salt temperatures require the more corrosion resistant alloys, stainless steel 316 and 800H. Characterization of the sample surfaces revealed the presence of spinels at lower temperatures, while Fe2O3 was the dominant iron oxide at higher temperatures for each alloy.

Corrosion testing device for in-situ corrosion characterization in operational molten salts storage tanks: A516 Gr70 carbon steel performance under molten salts exposure

Concentrated solar power (CSP) generation is becoming a very important player within the renewable energy sector thanks to increased introduction of these facilities into the conventional electricity market. CSP plants become dispatchable when integrating thermal energy storage (TES) systems which allow electricity production at any time of the year. Sensible TES using nitrate salts mixtures as storage fluid are the most extended arrangement for commercial CSP facilities. In addition to storage time, dimensions, thermal-mechanical requirements, among others, corrosion compatibility between high temperature nitrate salts, and structural materials is a key factor to take into consideration for the final storage system design. Many scientific contributions have been developed regarding metallic alloys corrosion performance in nitrate salts at laboratory scale. Accordingly, lack of technical background is identified about nitrates corrosion in relevant operation conditions. Therefore, a corrosion testing device (CTD) was designed to evaluate corrosion behavior of structural materials inside high temperature nitrate salts storage tanks in operation. Furthermore, A516 Gr70 carbon steel was evaluated at different exposures times by using the CTD in the TES-PS10 pilot plant. Results reported within this study show the feasibility of the CTD to be used at commercial scale allowing corrosion preventive maintenance practices and materials selection optimization. Moreover, A516 Gr70 carbon steel displayed an excellent corrosion performance after nitrate salts exposure being recommended for long time service under continuous and intermittent exposure to nitrate salts. In addition to low corrosion rates, carbon steel generated protective and well adhered iron oxide layers without significant localized phenomena. Finally, negligible susceptibility to crevice and stress corrosion cracking (SCC) phenomena is showed by carbon steel under test conditions.

High Temperature Oxidation of 9-12% Cr Materials P91 and P92 in Supercritical Water

The article summarizes the results obtained within a project PRAMEK. The project is focused on corrosion behavior of structural materials in water environment with supercritical parameters. Ferritic - martensitic materials P91 and P92 was evaluated. Multi-layered oxide was created on materials sample surface after 1000 hours long exposures in Supercritical Water Loop (SCWL) and Supercritical Water Autoclave (SCWAc) under SCWR operational parameters (600 °C, 25 MPa). The outer layer consisted of magnetite was porous and may tend to exfoliate. The inner layer is formed by spinel with Cr and Fe oxides. Microstructure of materials P91 and P92 and surface oxidic scales were evaluated by means of light and scanning electron microscopy equipped with wave and energy spectroscopy.

Corrosion Issues of High Temperature Reactor Structural Metallic Materials

Cooling helium of high temperature reactors (HTRs) is expected to contain a low level of impurities: oxidizing gases and carbon-bearing species. Reference structural materials for pipes and heat exchangers are chromia former nickel base alloys, typically alloys 617 and 230. And as is generally the case in any high temperature process, their long term corrosion resistance relies on the growth of a surface chromium oxide that can act as a barrier against corrosive species. This implies that the HTR environment must allow for oxidation of these alloys to occur, while it remains not too oxidizing against in-core graphite. First, studies on the surface reactivity under various impure helium containing low partial pressures of H2, H2O, CO, and CH4 show that alloys 617 and 230 oxidize in many atmosphere at intermediate temperatures (up to 890–970°C, depending on the exact gas composition). However when heated above a critical temperature, the surface oxide becomes unstable. It was demonstrated that at the scale/alloy interface, the surface oxide interacts with the carbon from the material. These investigations have established an environmental area that promotes oxidation. When exposed in oxidizing HTR helium, alloys 617 and 230 actually develop a sustainable surface scale over thousands of hours. On the other hand, if the scale is destabilized by reaction with the carbon, the oxide is not protective anymore, and the alloy surface interacts with gaseous impurities. In the case of CH4-containg atmospheres, this causes rapid carburization in the form of precipitation of coarse carbides on the surface and in the bulk. Carburization was shown to induce an extensive embrittlement of the alloys. In CH4-free helium mixtures, alloys decarburize with a global loss of carbon and dissolution of the pre-existing carbides. As carbides take part in the alloy strengthening at high temperature, it is expected that decarburization impacts the creep properties. Carburization and decarburization degrade rapidly the alloy properties, and thus result in an unacceptably high risk on the material integrity at high temperature. Therefore, the purification system shall control the gas composition in order to make this unique helium atmosphere compatible with the in-core graphite, as well as with structural materials. This paper reviews the data on the corrosion behavior of structural materials in HTRs and draws some conclusions on the appropriate helium chemistry regarding the material compatibility at high temperature.

Corrosion of Structural Materials in Liquid Lead Alloys for Nuclear Applications

Abstract The corrosion behavior of structural materials in liquid lead alloys like Pb-17Li as a liquid tritium breeder for future fusion reactors and Pb-55Bi (lead-bismuth eutectic [LBE]) as an env...

Effects of Noble Metal Deposition upon Corrosion Behavior of Structural Materials in Nuclear Power Plants, (I)

The effects of noble metal deposition under hydrogen water chemistry (HWC) condition on the features of oxide film formed on structural components in a reactor were studied. Noble metal-deposited type 304 stainless steel specimens with an oxide film were exposed to the simulated HWC condition, including co-existing Co radioactivity. Relationships between features of the oxide film which had two layers and the accumulation and distribution of Co radioactivity in the oxide film were established. The outer layer of the oxide film which consisted of α-Fe2O3, Fe3O4 and NiFe2O4 was dissolved by noble metal deposition and exposure to the HWC condition. The reasons for this were as follows. Solubility of α-Fe2O3, Fe3O4 and NiFe2O4 increased with the decrease of electrochemical corrosion potential. Dissolution of these compounds was accelerated by the anodic reaction of hydrogen which is catalyzed by noble metal. Co radioactivity was mainly incorporated into the inner layer. This was caused by the substitution of radioactive Co ions for ferrous ions in the oxide film, based on the observation that growth of the oxide film and oxidation of base metal stopped in the HWC condition. The inner layer consisted of FeCr2O4 which is stable at low ECP and it did not dissolve. Co radioactivity was not incorporated into the outer layer because it dissolved.

Effects of Noble Metal Deposition upon Corrosion Behavior of Structural Materials in Nuclear Power Plants, (I): Effect of Noble Metal Deposition with an Oxide Film on Type 304 Stainless Steel under Simulated Hydrogen Water Chemistry Condition

The effects of noble metal deposition under hydrogen water chemistry (HWC) condition on the features of oxide film formed on structural components in a reactor were studied. Noble metal-deposited type 304 stainless steel specimens with an oxide film were exposed to the simulated HWC condition, including co-existing Co radioactivity. Relationships between features of the oxide film which had two layers and the accumulation and distribution of Co radioactivity in the oxide film were established. The outer layer of the oxide film which consisted of α-Fe2O3, Fe3O4 and NiFe2O4 was dissolved by noble metal deposition and exposure to the HWC condition. The reasons for this were as follows. Solubility of α-Fe2O3, Fe3O4 and NiFe2O4 increased with the decrease of electrochemical corrosion potential. Dissolution of these compounds was accelerated by the anodic reaction of hydrogen which is catalyzed by noble metal. Co radioactivity was mainly incorporated into the inner layer. This was caused by the substitution of radioactive Co ions for ferrous ions in the oxide film, based on the observation that growth of the oxide film and oxidation of base metal stopped in the HWC condition. The inner layer consisted of FeCr2O4 which is stable at low ECP and it did not dissolve. Co radioactivity was not incorporated into the outer layer because it dissolved.

高温ナトリウム中におけるオーステナイト・ステンレス鋼の腐食速度評価式

For the design of the liquid metal fast breeder reactor, the corrosion behaviors of austenitic stainless steels SUS 304, 316 and 321 were investigated in high temperature flowing sodium.Such factors as sodium exposure time, downstream factor, sodium temperature and oxygen content in sodium are considemed as main factors of sodium environment which influence the corrosion behavior of structural materials. The empirical corrosion equation derived by statistical analysis of available corrosion data isCR=3.08×105·O20.8·exp(-22, 000/RT-0.0059(L/D))where CR: Corrosion rate (μm/yr), O2: Oxygen content in sodium (ppm)R: Gas constant (1.98cal/mol·K), T: Sodium temperature (K)L/D: Downstream factor in length/diameter ratio.This equation is applicable to austenitic stainless steels at oxygen content of 1-10ppm, temperature of 500-650°C, downstream factor below 200 and velocities of 2-4m/s.