Durability evaluation of Ni‐Cr‐Mo super alloys in a simulated scrubbed flue gas environment

Abstract

Results of DC electrochemical measurements of four Ni-base alloys are presented. The tests were conducted in 1 percent sulphuric acid, containing 0.2 percent chlorides at temperature 353K. Gravimetric test, performed in the same conditions, revealed excellent properties of alloy signed A3. Pitting corrosion of alloy A4 at the test conditions after long exposure at 353K was observed and was confirmed by the applied tests. The multiple anodic polarization (MAP) method is proposed to control alloys' susceptibility to pitting corrosion.

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

“…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.…”

“…Combined with the observation about corrosion morphology, it is concluded that the more severe intergranular corrosion is the dominant corrosion behavior of the C22 coating, comparing to that of C22 bulk. The molybdenum-depleted region adjacent to the molybdenum-segregated region in the eutectic is preferentially attacked, resulting in the primary grain-eutectic bond weakening and leading to the intergranular corrosion [36,40,71]. Simultaneously, the formation of chromium containing corrosion products causes the chromium depletion in the eutectic, and further degrades the corrosion resistance [48,49,69].…”

“…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.…”