The influence of the manufacturing process of semifinished products (forging, solution annealing, and aging) on the structure and corrosion properties of the EP718 nickel-based alloy (KhN45MVTYuBR) used in the oil and gas industry is investigated. The corrosion-electrochemical properties of the alloy are determined using gravimetric and electrochemical techniques. The microstructure is studied by optical and transmission electron microscopy. It is shown that the EP718 alloy in the delivery state (without heat treatment) has the highest corrosion resistance, and its corrosion properties degrade during subsequent solution annealing at 1080°C.