The Role of Copper on the Crevice Corrosion Behavior of Nickel-Chromium-Molybdenum Alloys in Aggressive Solutions

Abstract

The effect of Cu on the localized corrosion of Ni-Cr-Mo alloys has been investigated in hot saline solutions by comparing the behavior of N06059 and N06200 alloys, using electrochemical and surface analytical techniques. No measurable effect of copper on anodic film growth kinetics and passive film properties was detected and the breakdown and repassivation potentials of the alloys were very similar. Angle-resolved x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy demonstrated that the copper segregated to the oxide/solution interface during anodic film growth and that this process was enhanced as the pH decreased, as would occur in a crevice prior to initiation. Galvanostatically controlled crevice corrosion experiments demonstrated that this surface accumulation suppressed the metastable breakdown events that preceded initiation on the Cu-free alloy. Dynamic secondary ion mass spectrometry showed that copper accumulated with molybdates in crevice corroded locations but could not confirm any influence of copper on crevice propagation.

Performance of Corrosion-Resistant Alloys in Concentrated Acids

“…Crook [26,27], an inventor of the Cu-containing C-2000 alloy, investigated the corrosion performance of this alloy in a wide range of corrosive media and clearly demonstrated a higher uniform corrosion resistance of C-2000 alloy compared to other corrosion-resistant Ni-Cr-Mo alloys in H 2 SO 4 acid. Although more characterization study is needed to understand the role of Cu in C-2000 alloy, the present and previous studies [24][25][26][27] clearly support the notion that the presence of Cu (1.6 wt%) in C-2000 alloy (Table 1) enhances the uniform corrosion resistance performance in reagent grade H 2 SO 4 acid. Except C-2000 alloy, the ranking of various Ni-Cr-Mo (W) alloys based on its corrosion resistance performance in HCl and H 2 SO 4 behaves similarly, i.e., higher the Mo (or Mo ?…”

“…The corrosion data show that C-2000 alloy has a much higher corrosion resistance in H 2 SO 4 acid than expected. In a recent study, Mishra et al [24] investigated the oxide film formation on C-2000 alloy at different pH using angleresolved x-ray photoelectron spectroscopy (AR-XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was observed from the surface-sensitive techniques that the copper segregated to the oxide/solution interface during anodic film growth and this process was enhanced as the pH decreased.…”

Materials Selection for Use in Concentrated Hydrochloric Acid

“…The experimental details and the electrochemical techniques utilized when using these arrangements have been reported elsewhere. 7,[10][11][12] The electrolyte used for crevice corrosion experiments was 1 M NaCl. In SCA, the temperature selected was 105°C and a galvanostatic current of 20 μA was applied to guarantee crevice initiation and to control its propagation.…”

Corrosion Study of Base Material and Welds of a Ni–Cr–Mo–W Alloy

“…An addition of the optimum amounts of chromium (Cr), molybdenum (Mo) and tungsten (W) significantly increases the corrosion resistance in both reducing (like HCl, H 2 SO 4 ) and oxidizing environments (like HNO 3 ) as well as its resistance to localized corrosion [1,2,6]. For applications in HF and H 2 SO 4 , Fe-and Ni-based alloys containing Cu exhibit an enhanced corrosion resistance performance [7][8][9][10][11][12]. In Crrich alloys, Cr primarily forms a passive film of Cr 2 O 3 on the surface, thereby imparting better passivation properties [6,[13][14][15][16].…”

“…While the corrosion characteristics of wrought Fe and Ni alloys have been widely studied [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], there is not much information regarding the corrosion behavior of their welds, although the welded regions are generally thought to be more prone to corrosion attack in aggressive environments. In the past, limited corrosion data have been generated for as-welded coupons in acidic solutions, but using this approach it is difficult to determine the individual susceptibility of the base metal and welded region to corrosion attack.…”