Microstructural Characterization of the Corrosion Product Deposit in the Flow-Accelerated Region in High-Temperature Water

Abstract

The clogging behavior of the micro-orifice under a flow accelerated condition was investigated after 500 h of immersion in high-temperature water. The results indicated the residual area of the micro-orifice was reduced to one-third of its original size after 500 h of immersion due to the deposition of corrosion products. In this process, the clogging behavior of micro-orifice can be divided into three stages: the stable deposition stage, the quick recovery stage, and the dynamic equilibrium stage. The corrosion products were porous and consisted of many deposited particles. The process of particle deposition and removal was carried out simultaneously.

Microstructural Understanding of Flow Accelerated Corrosion of SA106B Carbon Steel in High-Temperature Water with Different Flow Velocities

“…In the secondary circuit pipes, the pH value of high-temperature water was controlled at 9.7, avoiding the occurrence of FAC caused by a low pH value [20] and preventing the stress corrosion cracking of the steam generator caused by a high pH value [21]. At the same time, the DO value was also controlled at below 10 ppb to avoid under-deposit corrosion caused by the deposition of oxide on the surface of the heat-exchange tubes [22,23]. Based on the actual operating temperature of the secondary circuit [6], and in order to study the FAC mechanism at extreme temperature, the test temperature was selected as 290 • C. Thus, the FAC test conditions and water chemistry parameters in this study can be summarized in Table 2.…”

Flow-Assisted Corrosion of Carbon Steel in Simulated Nuclear Plant Steam Generator Conditions

“…The dissolution rate is, in fact, equal to the sum of the current densities of the dissolution of the oxide and transfer of iron ions from the metal through the oxide layer, which emphasizes its role as one of the controlling factors of FAC [10,11]. Several works [13][14][15][16][17] have been devoted to the characterization of the thin iron oxide layers formed on the carbon steel components under the chemical and hydrodynamical conditions prevailing within the secondary circuit of PWR plants (de-aerated and alkaline turbulent water or wet steam). However, the mechanism of the process has not been studied in detail with electrochemical methods.…”