An Overview of Internal Oxidation as a Possible Explanation of Intergranular Stress Corrosion Cracking of Alloy 600 in PWRS

Abstract

The main purpose of the present paper is to compare the results of recent high resolution microscopy of intergranular stress corrosion cracking of alloy 600 in various environments encountered during the operation of PWRs with the hypothesis that cracking is caused by the phenomenon of internal oxidation. Some of the points of criticism, which have arisen as to the applicability of the internal oxidation mechanism at typical PWR operating temperatures and corrosion potentials, are also addressed. These are specifically the problem of reconciling the apparent rate of intergranular diffusion of oxygen in nickel base alloys with the observed rates of cracking and the thermodynamic requirement for internal oxidation that the corrosion potential be at or below the Ni/NiO redox potential. The latter point is of particular concern if this mechanism is invoked to explain secondary side steam generator tube IGA/IGSCC.

Effect of electropolishing on corrosion of Alloy 600 in high temperature water

“…Before peak fitting, the possible eigen values were determined by analyzing all data. In the case of Cr, for example, three eigen spectra were identified to be corresponding to Cr(0), Cr(OH) 3 and Cr(III) in oxides. Then analysis of the data was performed via XPSpeak4.1 peak fitting software.…”

“…An ultra-thin film consisting of a small amount of Cr oxide, Ni oxide and Ni(OH) 2 was observed on the CSP, with a maximum Cr(III) concentration of ∼13 at%. On the other hand, the EPS shows a much thicker film consisting of Cr(III) in oxides, Cr(OH) 3 and Ni(OH) 2 , with a maximum Cr(III) concentration of ∼27 at%. The speciated composition profiles suggest that a Crenriched, continuous oxide film was formed on the EPS while there is no such a layer on the CPS.…”

“…Stress corrosion cracking (SCC) of structural materials is one major concern in light water reactors, which is a synergic effect of material, mechanics, and environment [1][2][3][4]. According to internal oxidation and slip-dissolution/oxidation mechanisms, surface corrosion behaviour plays an important role in SCC initiation process [5][6][7][8][9][10][11][12].…”

Failure Analysis of a Chain Link Used in Charger Drive of a Coke Oven Battery

“…It occurs when the oxygen potential at the reaction site in the steel is less than the equilibrium oxygen potential of the solvent metal (Fe) oxide and the concentrations of oxygen and the alloying elements (e.g., Si, Mn, etc.) are sufficient to exceed those corresponding to the solubility product of the oxide in the steel [4,5].…”

Evaluation of Primary Water Stress Corrosion Cracking Resistance of Three Heats of Alloy 600 in 400 °C Hydrogenated Steam Condition

“…However, due to the complexity of the inter-relationship among the above mentioned factors, it is difficult to identify the dominant factors affecting the PWSCC susceptibility of Alloy 600. This could be the reason that the suggested PWSCC mechanisms, such as internal oxidation, hydrogen embrittlement, and film rupture models, were not able to explain all the PWSCC dependencies with those factors [8][9][10][11][12]. In the laboratory, it is usual to do the PWSCC test at the accelerated condition.…”