Hastelloy valves and titanium alloy valves are common options for heavily corrosive service conditions. Their corrosion resistance has respective strengths; neither is universally superior. The better material depends on the type, concentration and temperature of the process medium.
What Is Hastelloy Alloy and Its Corrosion Resistance Features
Hastelloy is a nickel-based alloy built on nickel, chromium and molybdenum. It excels in strongly reducing and mixed acid environments. Its high molybdenum content (e.g., 16% molybdenum in C-276) delivers reliable resistance to non-oxidizing acids such as hydrochloric acid, dilute sulfuric acid and phosphoric acid. In boiling 10% hydrochloric acid, it shows an extremely low corrosion rate, far outperforming conventional stainless steel. Meanwhile, it features outstanding resistance to pitting corrosion, crevice corrosion and stress corrosion cracking. It withstands chlorine-containing media including wet chlorine and hypochlorites, with a wide applicable temperature range and stable performance under high-temperature corrosive conditions. However, Hastelloy’s corrosion resistance degrades in concentrated nitric acid and high-temperature strongly oxidizing media, and it is not resistant to hydrofluoric acid.
What Is Titanium Alloy and Its Corrosion Resistance Features
Titanium alloy gains its corrosion resistance from a dense, self-healing TiO₂ passive film on its surface, delivering excellent performance in oxidizing and neutral environments. It remains highly stable in concentrated nitric acid, wet chlorine, seawater and chloride solutions. It barely corrodes in 50% nitric acid at room temperature, with a salt spray corrosion rate only one-thousandth that of stainless steel. Titanium alloy has low density and high strength, suited for lightweight corrosion-resistant applications in marine engineering and chemical industries. It has notable drawbacks though: it cannot resist hydrofluoric acid, and crevice corrosion or even spontaneous combustion may occur in high-concentration chloride media or dry chlorine gas at temperatures above 100°C.
By comparison: Hastelloy performs better in reducing acids, high-temperature mixed corrosion and heavily corrosive chlorine-containing environments. Titanium alloy is more suitable for concentrated nitric acid, wet chlorine, seawater and oxidizing media at ambient temperature. Neither material works if the medium contains hydrofluoric acid. For extremely complex service conditions, comprehensive evaluation combining temperature and concentration is required.
Conclusion
In summary, Hastelloy is an all-round high-performance corrosion-resistant material, while titanium alloy is the top choice specifically for oxidizing media. Material selection shall be based on working medium conditions to determine the most suitable corrosion-resistant solution.
