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Nitric acid (HNO3), as an important strong oxidizing inorganic acid, plays a key role in fields such as fertilizer production, dye synthesis, pharmaceutical intermediates, and nuclear fuel reprocessing. However, its dual properties of strong acidity and strong oxidizing power pose a significant corrosion threat to industrial equipment such as reactors, evaporators, storage tanks, pipelines, heat exchangers, and valves. Analyzing the electrochemical mechanism of nitric acid corrosion in systems and exploring advanced protection technologies hold significant engineering importance for improving equipment reliability, extending service life, and reducing life-cycle costs. Electrochemical mechanism of nitric acid corrosion: Nitric acid corrosion is primarily caused by the acidic effect of H⁺ ions and the strong oxidizing property of nitrate ions. In concentrated nitric acid (≥68%), HNO3 molecules readily decompose to release atomic oxygen, and its oxidizing power increases with rising concentration and temperature ； In dilute nitric acid, the corrosion process exhibits distinct autocatalytic characteristics. Electrochemical studies show that the cathodic reaction in nitric acid media proceeds primarily via nitrous acid (HNO₂) as an active intermediate: this autocatalytic cycle significantly accelerates the cathodic depolarization process, resulting in an increased rate of dissolution of the anodic metal. At the same time, dissolved metal ions (such as Fe³⁺ and Cr6⁺) increase the redox potential of the solution, causing the material to transition from a passivated state to an over-passivated state, which in turn leads to intergranular corrosion. In vapor or condensate environments, due to the thin liquid film and high surface area-to-volume ratio, the diffusion of corrosion products is restricted, the autocatalytic effect becomes more pronounced, and the risk of localized corrosion increases significantly. Stainless steel (such as 304L, 316L) often exhibits a transition from uniform corrosion to intergranular corrosion in nitric acid, especially under conditions of high temperature, high concentration, or the presence of oxidizing impurities. Although titanium and titanium alloys can form a stable TiO₂ passivation film, they may still experience accelerated dissolution in the area where high-temperature nitric acid vapor condenses. Corrosion manifestations and risk assessment in industrial equipment: In nitric acid production and utilization facilities, equipment is often subjected to issues such as uniform corrosion, pitting corrosion, intergranular corrosion, and potential stress corrosion cracking. In an environment of high temperature and concentrated nitric acid, the corrosion rate of stainless steel can increase significantly, leading to thinning of the wall thickness and perforation/leaks. This not only affects process continuity but may also pose safety and environmental risks. Industrial equipment protection strategies against nitric acid corrosion involve the use of the following layered protection approaches in engineering practice: Optimization of material selection – appropriate alloys are chosen based on factors such as medium concentration, temperature, phase state, and impurities present. Stainless steel is suitable for medium and low concentrations of nitric acid ； In high-temperature or concentrated nitric acid environments, high-alloy stainless steels, titanium alloys, or rare metal materials should be considered. Surface engineering techniques: include passivation treatment, lining coatings, and diffusion alloying methods. Process and design control: reducing operating temperature, controlling the concentration of oxidizing ions, and optimizing equipment design to minimize dead zones and condensation deposits. Monitoring and maintenance: Real-time assessment is carried out through methods such as corrosion coupons, electrochemical noise, or ultrasonic thickness measurement. Tantalum surface alloying technology: A high-performance material for nitric acid protection. Key features of tantalum surface alloying technology: Excellent resistance to nitric acid corrosion: It exhibits an extremely low corrosion rate across all concentration ranges (from dilute to concentrated nitric acid), over a wide temperature range (from room temperature to above the boiling point), and in gas-liquid two-phase environments; this enables effective suppression of intergranular corrosion and self-catalytic acceleration effects. Excellent passivation film stability: The Ta₂O₅ film is not easily damaged in strongly oxidizing media, and it maintains its integrity over the long term even in nitric acid solutions containing metal ion impurities. Engineering economy: Compared to pure tantalum or high-nickel-based alloys, it significantly reduces material costs, while also facilitating surface strengthening modifications of large-scale equipment components such as heat exchange tubes, reactor internals, pipes, and valves. Long-term service capability: significantly extends the design life of equipment, reduces unplanned downtime and maintenance frequency, and optimizes the overall lifecycle cost of the system. In nitric acid evaporators, absorption towers, nuclear fuel reprocessing evaporation equipment, and fine chemical reaction systems, tantalum surface alloying technology has shown great potential for application. Conclusion and engineering recommendations: The mechanism of nitric acid corrosion involves multiple factors such as redox reactions, autocatalytic cycles, and the dynamic balance of passivation films; protective technologies require a combination of materials science, surface engineering, and process control methods. Tantalum-based surface alloy components, as an advanced surface modification technology, provide a long-lasting solution with high corrosion resistance and low cost for industrial equipment used in nitric acid-related applications. Statement: This article was originally published on the WeChat official account [Tantalum and Niobium New Technology Services and Applications]