Corrosion resistance of metal materials to sulfuric acid

Preface: With the rapid advancement of science and technology and the gradual updating of materials used by manufacturing enterprises, the application scope of steel plates/steel pipes resistant to sulfuric acid corrosion at low temperatures is expanding continuously, and they are increasingly favored by various manufacturing companies. The development of steel is inseparable from the support of anti-corrosion technologies; in particular, the corrosion resistance of structures has become a major issue of concern in the world today. In a sense, anti-corrosion technologies for steel are key factors in ensuring the proper use and durability of structural steel. Product introduction of ND steel used in boiler air economizers. Introduction to ND steel (1): 09CrCuSb (company code: ND) – steel plates and pipes resistant to corrosion caused by low-temperature sulfuric acid dew points. This is an excellent new product of ** grade, awarded the second prize for science and technology by Sinopec and the Ministry of Machinery; it also received the gold award at the World Expo organized by the ** Science and Technology Commission. In 1997, it was included in the GB150-1998 standard. In August 1999, it received a technical evaluation certificate issued by the National Pressure Vessels Committee and the **Technical Supervision Bureau. It has been included in the standard SH/T 3096-2001, \"Guidelines for the Design and Material Selection of Key Equipment for Processing High-Sulfur Crude Oil\". It is widely used in equipment such as economizers, air preheaters, heat exchangers, and evaporators that operate in flue gases with high sulfur content, as well as in various products that possess a certain degree of resistance to corrosion caused by sulfuric acid at low temperatures. ND steel is currently the most ideal material for resisting corrosion caused by low-temperature sulfuric acid at home and abroad. For seamless pipes and sheets made of 09CrCuSb (ND steel), the key performance criterion is that the corrosion rate after immersion in a 70°50% H2SO4 solution for 24 hours should not exceed 14 mg/cm•h. Compared to carbon steel, similar steel imported from Japan, and stainless steels, its corrosion resistance is 1.84 times that of Japanese CR1R steel, 2.97 times that of 1Cr18Ni9 steel, 8.63 times that of Corten steel, and 14.11 times that of Q235B steel. 09CrCuSb (ND steel) is a type of steel used in boilers ； Hot-rolled steel plates and steel tubes with excellent resistance to sulfuric acid dew point corrosion, developed for use in electric furnace heat exchange, flue pipes, chimneys, and similar applications. Its excellent resistance to sulfuric acid dew point corrosion, combined with its very high cost-performance ratio, makes it fully capable of replacing stainless steel; it is the best material in terms of resistance to sulfuric acid dew point corrosion. ND steel holds significant economic value and aligns with today’s concepts of efficiency, longevity, energy savings, and environmental protection – as well as with the guidelines for sustainable development. Introduction to ND Steel (2) -------------------------------------------------------------------------------- Standards of the People’s Republic of China for Steel Pressure Vessels GB150—1998. The technical requirements and usage specifications for seamless steel tubes made of H4 09CrCuSb (ND steel) intended for use in resisting sulfuric acid dew point corrosion are as follows: a) The chemical composition of the steel (as determined by melting analysis) is specified in H4; b) The mechanical properties of the steel tubes are specified in Table H5. c) The steel pipes shall be subjected to acid corrosion resistance tests; one sample shall be taken from every batch of 3 steel pipes, with each sample being a steel pipe 10 mm in length. Immersed in a 50% H2SO4 solution at a constant temperature of 70°C ± 2°C for 24 hours, the average corrosion rate for each sample shall not exceed 8.14 or 14 mg/cm•h; the specific values are specified in the order contract. Table H 4: Chemical composition (%) C Si Mn Cr Cu Sb P S ≤0.12 0.20–0.40 0.36–0.65 0.70–1.1 0.25–0.45 ≤0.1 ≤0.005 ≤0.035 Table H 5: Condition of delivery, Sampling direction, Wall thickness, Tensile test values – in mm, MPa, and % Normalized, longitudinal direction ≤7 390–550 ≥245 ≥25 d) Other technical requirements for steel pipes are specified in GB9948. e) Steel pipes are used for pressure-bearing components with a design pressure of p≤6.4Mpa. f) The operating temperature of the steel pipe is 0~400°C. g) The allowable stress for steel pipes is specified in Table H6. Table H 6: Steel grades and wall thickness in mm – ≤20, 100, 150, 200, 250, 300, 350, 400. For 09CrCuSb: ≤7, 130, 130, 130, 130, 128, 125, 119, 113. Note: Refer to point (3) in the introduction to ND steel. 09CrCuSb (ND steel) is currently the most suitable material for resisting corrosion caused by low-temperature dew points in sulfuric acid environments, both domestically and internationally. Seamless pipes made of 09CrCuSb (ND steel) are widely used in the manufacture of economizers, air preheaters, heat exchangers, and evaporators that operate in environments with high sulfur content, thereby helping to prevent corrosion resulting from dew points in such gases. ND steel also possesses resistance to nitrogen ion corrosion. The main performance indicator for 09CrCuSb (ND steel) pipes is that their corrosion rate in a 70-degree Celsius solution of 50% H2SO4 after 24 hours of immersion is not more than 14 mg/cm•h. Compared to carbon steel, similar Japanese-imported steels, and stainless steels, this material exhibits better corrosion resistance. After being used by major refineries, power plants, and manufacturing units both in China and abroad, the product has received widespread praise and achieved excellent performance. The specific data are shown in the table below: Steel grade: 09CrCuSb (ND steel); CRIR (Japan): 1Cr18Ni9; Corten S-TEN (Japan): A3 (Q235B). Corrosion rate: 7.30, 13.40, 21.70, 63.00; 27.4, 103.50. Multiples: 1, 1.84, 2.97, 8.63, 3.75, 14.11. Introduction to ND steel (4): Mechanical properties of 09CrCuSb (ND steel). The 09CrCuSb (ND steel) possesses good resistance to sulfuric acid corrosion, and its conventional mechanical properties are similar to those of 20–GB3087, as shown in Table 3. Table 3 Comparison of mechanical properties between 09CrCuSb steel and 20 steel. The Cr content added (0.70%–1.10%) to improve resistance to sulfuric acid corrosion also enhances the steel’s performance at higher temperatures. GB150—1998 specifies that the operating temperature for 09CrCuSb (ND steel) can reach 400°C. Its good elongation ensures good plasticity during bending processing. In addition, 09CrCuSb (ND steel) comes with guaranteed process properties upon delivery, including hydraulic testing at 20 MPa per pipe (compared to 10 MPa for 20 steel per GB3087), eddy current or ultrasonic testing (eddy current testing is generally required per GB3087 for 20 steel), and flattening tests for pipes with an outer diameter of 22–400 mm (with exactly the same requirements as specified in GB3087 for 20 steel). Introduction to ND steel (5): After adopting ND steel, Jinan Refinery saves 3.15 million yuan per year, while Jinzhou Petrochemical Company saves 1.35 million yuan per year. The use of ND steel not only helps to reduce costs but also ensures the safe operation of equipment and reduces environmental pollution; its social benefits are substantial. Conclusion: 09CrCuSb (ND steel) is a sulfuric acid corrosion-resistant steel that has undergone extensive testing and demonstrated excellent performance in various industrial applications. Its good corrosion resistance, along with its favorable physical and chemical properties as well as machinability, fully meet the requirements for design, manufacturing, and use. At the same time, 09CrCuSb (ND steel) exhibits strong corrosion resistance to hydrochloric acid (HCl), hydrofluoric acid (HF), sodium hydroxide (NaOH), and sodium chloride (NaCl).