Inhibition of Stress Corrosion Cracking of Alloy 600 in 10% Sodium Hydroxide Solution at 315°C

Nickel boride (NiB) as an inhibitor for an IGSCC of Alloy 600 and its applicability

“…4(d) except for very small cracks on the sample in FeB, no IG cracks were found on the samples tested in the boride containing solutions. This is very consistent with the results by Hur et al [11] who reported that the borides (TiB 2 and CeB 6 ) enhanced the SCC resistance of Alloy 600 in a 10% NaOH solution. The inhibition effectiveness of the borides here could not be quantitatively compared since all the samples failed mechanically before the IG cracks grew sufficiently enough.…”

“…It was found that, in the potential range between 150 and 200 mV above the OCP, Alloy 600 in a NaOH solution showed the highest SCC susceptibility [14,15]. Many experiments for evaluating the SCC susceptibility of Alloy 600 in caustic solutions have been performed at an applied potential between 150 and 200 mV above the open circuit potential (OCP) [9,11]. However, in the field the SCC phenomenon occurs at the open circuit potential of the alloy, so the effectiveness of an inhibitor should be evaluated for samples exposed to a caustic solution at the OCP as well as at a certain anodic potential.…”

“…Recently, Hur et al evaluated the effectiveness of inhibitors in terms of the crack depth on C-rings anodically polarized to 150 mV vs. the open circuit potential (OCP). They compared the effectiveness of TiO 2 , TiB 2 , and CeB 6 in the same condition and proposed cerium boride (CeB 6 ) as one of the most effective inhibitors [11]. This study was originally to verify the inhibition mechanism of boride.…”

Stress corrosion cracking of alloy 600 in an aqueous solution containing lead oxide

“…Figure 8 shows the elemental depth profiles of the surface oxides near the crack tips in the HTMA Alloy 600 specimens exposed to the water containing lead oxide with and without NiB for 300 h. The depth profiles show that the width of the Cr depletion zone is narrower and the enrichment of Ni in the oxide decreased in the solution with NiB. It has also been reported that adding CeB 6 to water containing lead oxide decreased the Cr depletion zone [17]. The higher SCC resistance of Alloy 600 in the test solutions with NiB and CeB 6 may be related to a chemical composition change such as recovery of Cr depletion in oxide, thus affecting the oxide properties.…”

Studies of microscopic strains on Alloy 600 surfaces arising from stress-corrosion cracking

“…Then an area of several hundred square microns was cleaned and polished with a focused gallium ion beam (FIB). The corrosion test of the C-ring was conducted so that, based on past practice [10,11], any stress-corrosion cracking of the sample would be slight. The C-ring was exposed in its stressed condition in an autoclave containing a solution of 10 wt.% NaOH in deionized water at a temperature of 315ºC.…”