Corrosion resistance of alloys in sulfuric acid at various concentrations and temperatures

Corrosion Behavior of a Ni–Cr–Mo Alloy Coating Fabricated by Laser Cladding in a Simulated Sulfuric Acid Dew Point Corrosion Environment

“…Moreover, the corrosion rate curves of the C22 coating at 50 • C and 70 • C present a similar trend, but the one at 60 • C presents a slight fluctuation. The corrosion rate at 60 • C has a negative value during 24 h-60 h, and the value after 72 h is slightly smaller than that at 50 • C. It is assumed that the localized corrosion and adhering corrosion products result in the unusual fluctuation, which was observed in the research on Ni-Cr-Mo alloy corrosion [38,39]. Hence, the measurement and calculation of corrosion rate were misled by this highly localized deterioration and incomplete removal of corrosion products [70].…”

“…It is inferred that both primary grains and secondary eutectics mainly consist of a γ-Ni solid solution, and the main distinction is the amount and type of solute elements. It is notable that the higher content Fe compared to C22 bulk is assumed to have a negative effect on the corrosion resistance of the C22 coating [35][36][37][38]. Meanwhile, the black micropores are corroded preferentially and become the nucleation of localized corrosion, leading to the degradation of corrosion resistance.…”

“…In terms of testing time effect, the corrosion rate curves of both C22 bulk and the C22 coating keep approximately horizontal. This implies that the initial oxidation film of C22 bulk and the C22 coating has excellent corrosion resistance to efficiently prevent severe damage, the further diffusion of the corrosion medium, and the charge transportation [35][36][37][38][39]. In contrast, the corrosion rate of TC4 and ND reduces as the testing time increases, and the extent of the reduction of ND is larger than that of TC4.…”

“…These formed smaller anode micro-batteries establish a micro-scale corrosion cell system and accelerate the intergranular corrosion [50,66]. Both the corrosion reaction and the electrochemical reaction are to a certain extent controlled by the ion diffusion process in the testing solution; therefore, the corrosion rate of the C22 coating increases with the increase in temperature [36,38,72]. The synergistic effect of a high Fe content and black micropores resulting from the laser cladding process is considered as the primary cause of the degraded corrosion resistance of the C22 coating compared with that of C22 bulk.…”

“…High performance nickel-based alloys have been utilized in preheater, FGD systems, backend ductworks, etc., to extend the service life to several decades. Among the nickel-based alloys, the Ni-Cr-Mo alloy is the most widely used because of its excellent property in preventing acid corrosion, pitting, and crevice corrosion [13,[34][35][36][37][38][39][40][41]. Moreover, the corrosion behavior of the Ni-Cr-Mo alloy has been widely studied.…”