Abstract
Environmentally assisted cracking (EAC) is a very complex process that develops in materials that involve combining actions of environment and tensile loading. Crack initiation is the least explored stage and is not clearly defined. For this paper, current knowledge of crack initiation mechanisms was reviewed for three types of commercial structure materials exposed to high-temperature (HT) water coolants of power plants, namely ferritic low-alloy (LAS) and carbon (CS) steels, austenitic stainless (AS) steels, and nickel-based alloys. Physicochemical microprocesses engaged in the two earliest phases of the mechanism, the precursor and the incubation phases, are rather specific for each of these materials. In the latter, the slow growth phase, the crack development process passes into a sequence of repeating steps where the specific key microprocesses persist.
Highlights
Assisted cracking (EAC) is a significant degradation process for components of high-temperature (HT) water-cooled power systems [1,2]
This review summarizes the current knowledge of Environmentally assisted cracking (EAC) initiation in three selected corrosion systems, namely the ferritic low-alloy and carbon steels, austenitic stainless steels, and Ni-based alloys, exposed to high-temperature water and load
It appears that no clear conclusion can be drawn about the conditions under which a crack embryo can emerge in these materials, due to many interrelated and time-dependent factors involved in the process
Summary
Assisted cracking (EAC) is a significant degradation process for components of high-temperature (HT) water-cooled power systems [1,2]. In the light-water-cooled nuclear reactor (LWR) systems, high-temperature (HT) water continuously flows along the surface of components and it can—after long-term operation— create suitable conditions for EAC initiation. It is well known what basic physicochemical processes take place. This paper reviews the current knowledge about EAC initiation mechanisms occurring in three types of structure materials, namely ferritic low-alloy (LAS) and carbon (CS) steels, austenitic stainless (AS) steels, and Ni-based alloys, which are typical structure materials of LWR system components. A hydrogen partial pressure of ~0.17 to 0.65 bar is maintained above the subcooled primary water at ~150 bars and 280 to 325 ◦C in order to suppress the radiolytic decomposition of water, which has the effect of localizing redox and corrosion potentials of most structural alloys close to the redox potential of the Ni/NiO equilibrium [11]
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