Modelling and Analysis of the Corrosion Characteristics of Ferritic-Martensitic Steels in Supercritical Water

Abstract

The dependencies of weight gain of 9-12 Cr ferritic-martensitic steels in supercritical water on each of seven principal independent variables (temperature, oxygen concentration, flow rate, exposure time, and key chemical composition and surface condition of steels) have been predicted using a supervised artificial neural network (ANN). The relative significance of each independent variable was uncovered by fuzzy curve analysis, which ranks temperature and exposure time as the most important. The optimized ANN, not only satisfactorily represents the experimentally-known non-linear relationships between the corrosion characteristics of F-M steels and the key independent variables (demonstrating the effectiveness of this technique), but also predicts and reveals that the effects of oxygen concentration on the weight gains, to a certain degree, is influenced by the flow rate and temperature. Finally, according to the ANN predicted-results, departure of oxidation kinetics from the parabolic law, and basic cause of chromium content in steel substrate influencing the corrosion rate, and the synergetic effects of dissolved oxygen concentration, flow rate, and temperature, are discussed and analyzed.

The evolution and characterisation of the corrosion scales formed on 3Cr steel in CO2-containing conditions relevant to geothermal energy production

“…The formation of the spinel structure FeCr2O4 is via the reaction (15). The Fe 3+ sites occupy by Cr 3+ in the spinel structure improves the film protectiveness of the inner layer owing to the stronger binding energy replaced by Cr-O bond [22] . The involvement of Cr in the inner layer decreases the corrosion rate as shown in Figure 3 and gradually reduces the metal ion diffusion throughout the inner layer.…”

Supercritical Water Oxidation for Environmentally Friendly Treatment of Organic Wastes

“…In order to decrease corrosion rate, it is better to adjust the solution density to be below 200 kg/m 3 [31], which may result from the variation in corrosion mechanisms at high-or low density aqueous systems. Lots of studies have been carried out on the mechanism of corrosion scales grown on metal materials in SCW [29,45,46]. Two typical mechanisms, such as solid-state growth mechanism and mixed model (formation of the inner layer by solid-state growth process and formation of the outer layer by a metal dissolution-oxide precipitation mechanism) depending on the water density below or above 100-200 kg/m 3 , have been proposed [24,29,45,47,48].…”

Oxidation Processes and Involved Chemical Reactions of Corrosion-Resistant Alloys in Supercritical Water

“…The diffusion coefficients of Fe and Cr in volume and in grain boundary can be calculated by the following equations: 39,47 i k j j j y { z z z D RT 1. 6…”

“…It is a significant option in the six generation nuclear power plant design due to many advantages, such as fuel cycle sustainability, waste minimization, good economics, safety, reliability, and enhanced proliferation resistance. − However, its efficiency improvement requires higher temperature and pressure of steam in high-temperature pipelines and facilities including superheater and reheater . The dramatical change of water properties from subcritical to supercritical state affects significantly the interaction between water and structural material. , SCW is considered to be more corrosive to metal material, compared with water or steam in traditional nuclear reactors (i.e., light water reactor and pressurized water reactor) . The high temperature and oxidative nature of SCW increases the corrosion rate of alloy and the exfoliation rate of the corresponding oxide scale so reducing the mechanical stability of the used material.…”

“…1,5 SCW is considered to be more corrosive to metal material, compared with water or steam in traditional nuclear reactors (i.e., light water reactor and pressurized water reactor). 6 The high temperature and oxidative nature of SCW increases the corrosion rate of alloy and the exfoliation rate of the corresponding oxide scale 7 so reducing the mechanical stability of the used material. Similarly, the chemical and electrochemical corrosion of structural material has also become a key problem in developing a supercritical water oxidation reactor for organic waste treatment due to high temperature, pressure, and oxygen content.…”