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I. Basic Characteristics of 2205 Duplex Stainless Steel 2205 duplex stainless steel is a type of ferrite-austenite duplex stainless steel, with a typical chemical composition of 22% chromium, 5% nickel, 3% molybdenum, and 0.15% nitrogen. Its microstructure consists of approximately 50% ferrite and 50% austenite, endowing it with unique “dual advantages”: – **High strength**: Its yield strength is about twice that of conventional 304/316 stainless steel, enabling the reduction of equipment wall thickness and lowering of manufacturing costs. – **Excellent corrosion resistance**: It performs exceptionally well in media containing chloride ions, sulfuric acid, sulfurous acid, etc. – **Good resistance to stress corrosion cracking (SCC)**: It is far superior to austenitic stainless steel in high-temperature, high-humidity environments containing chloride ions. – **Favorable weldability**: Reasonable welding processes can prevent sigma phase precipitation and maintain microstructural stability. II. Corrosive Environment Challenges in Desulfurization and Denitrification Systems In the wet limestone-gypsum desulfurization system, flue gas forms acidic slurry with a pH value of 1–5 after spray washing, which contains high concentrations of chloride ions (up to tens of thousands of ppm), fluoride ions, sulfate ions, as well as unreacted sulfuric acid/sulfurous acid. Meanwhile, ammonia may remain in the flue gas after denitrification, which subsequently reacts with sulfur dioxide to form ammonium bisulfate (ABS), a substance with strong corrosivity and adhesiveness. Such environments are prone to causing the following corrosion problems: – **Pitting corrosion and crevice corrosion**: Especially at welds and flange connections. – **Stress corrosion cracking (SCC)**: 304/316 stainless steel is highly susceptible to failure in chloride-containing environments above 60°C. – **Erosion-corrosion**: High-velocity slurry exerts combined effects of abrasion and corrosion on pipe elbows and nozzles. III. Practical Application Performance of 2205 Duplex Stainless Steel 1. Outstanding Corrosion Resistance A large amount of field operation data shows that the service life of 2205 duplex stainless steel in components such as FGD absorber liners, slurry circulation pipelines, demister support beams, and oxidation air pipe networks is significantly longer than that of 316L stainless steel. Its critical pitting temperature (CPT) is usually above 70°C, providing sufficient safety margin under typical desulfurization operating conditions (50–65°C). In addition, its pitting resistance equivalent number (PREN = %Cr + 3.3×%Mo + 16×%N) is approximately 34–38, much higher than the 24–26 of 316L, indicating stronger resistance to localized corrosion. 2. Strong Resistance to Stress Corrosion Cracking In coastal power plants or systems using seawater for cooling, chloride ion concentration is extremely high, and 316L often fails prematurely due to SCC. In contrast, the ferrite phase in 2205 duplex stainless steel effectively inhibits crack propagation, and it has achieved over 10 years of trouble-free operation in multiple high-chloride projects. 3. Economic Efficiency and Whole-Life Cycle Cost Advantages Although the unit price of 2205 duplex stainless steel is about 2–3 times that of 316L, its high strength allows for the design of thinner wall thicknesses, reducing material consumption. More importantly, its ultra-long service life significantly cuts down maintenance frequency, production shutdown losses, and replacement costs. A retrofit case of a large domestic power plant shows that after replacing the original 316L slurry pipelines with 2205 duplex stainless steel, the maintenance cycle was extended from 2 years to over 8 years, and the comprehensive cost was reduced by about 30%. IV. Application Precautions Despite its superior performance, the following points should be noted when applying 2205 duplex stainless steel in desulfurization and denitrification systems: – **Welding control**: Low heat input and rapid cooling processes should be adopted to avoid 475°C embrittlement or sigma phase precipitation. – **Avoid long-term high-temperature service**: Its mechanical properties and corrosion resistance may degrade when operating above 300°C. – **Not suitable for strong reducing acid environments**: Such as high-concentration hydrochloric acid, where super duplex stainless steel or nickel-based alloys should be considered instead. Conclusion With its high strength, excellent resistance to chloride ion corrosion and stress corrosion cracking, 2205 duplex stainless steel demonstrates outstanding application effects in desulfurization and denitrification systems. It not only improves the reliability and safety of environmental protection equipment but also achieves significant economic benefits throughout the whole life cycle. With the maturity and cost optimization of duplex stainless steel smelting and processing technologies, its application prospects in the field of environmental protection engineering will be broader. For newly-built or retrofitted FGD/SCR systems, 2205 duplex stainless steel is undoubtedly an ideal choice that balances performance and cost. #2205DuplexStainlessSteel #DesulfurizationDenitrification #CorrosionResistance #IndustrialMaterialApplication #FGDSystem #stainlesssteel