Alloy 20 vs Hastelloy C276 Corrosion Comparison
Alloy 20 vs Hastelloy C276 Corrosion Comparison
Alloy 20 is well-suited for use in sulfuric acid concentrations of 20-40% and general corrosive environments, but its corrosion resistance is not as good as Hastelloy C276. Due to its higher molybdenum and tungsten content, Hastelloy C276 offers superior corrosion resistance to a wider range of corrosive chemicals (hydrochloric acid, mixed acids, chlorides), making it the preferred material for the harshest environments despite its higher cost. For acidic media applications, Alloy 20 is a more cost-effective option than stainless steel, while C276 is better suited for extreme reducing/oxidizing conditions, pitting corrosion, and crevice corrosion.
Is C276 alloy a type of Hastelloy alloy?
Hastelloy C276 is one of the few alloys that can withstand corrosion from wet chlorine gas, hypochlorite, and chlorine dioxide solutions. Hastelloy C276 exhibits excellent corrosion resistance to strong oxidizing salt solutions (such as ferric chloride and cupric chloride).
Hastelloy C-276 is a nickel-molybdenum-chromium-tungsten superalloy (Hastelloy) whose core advantage is its almost universal corrosion resistance. It effectively resists extreme corrosive media such as strong oxidizing and reducing acids, mixed acids, chlorides, wet chlorine gas, and harsh acidic salt solutions, and exhibits exceptional performance in resisting pitting corrosion, crevice corrosion, and stress corrosion cracking. It is specifically designed for the most corrosive industrial environments, such as hydrometallurgy, chemical and pharmaceutical industries, flue gas desulfurization, waste incineration, and marine engineering, making it one of the top engineering materials with the broadest corrosion resistance range among commercially available alloys.
Alloy 20 is a nickel-iron-chromium austenitic stainless steel (commonly known as Carpenter 20 or CN7M). Its core characteristic is the significant improvement in resistance to reducing acids such as sulfuric acid and phosphoric acid, as well as chloride stress corrosion cracking, achieved through the addition of elements such as copper and molybdenum. It is particularly suitable for demanding conditions in the chemical, food, pharmaceutical, and nuclear fuel processing industries, especially for sulfuric acid storage equipment, chemical reactors, mixed acid environments, and high-temperature acidic media. It is a specialized acid-resistant stainless steel that balances corrosion resistance, weldability, and mechanical properties.
Chemical composition of Hastelloy C276 and Monel 400 alloys
| Element | Hastelloy C-276 (wt%) | Alloy 20 (Carpenter 20) (wt%) |
|---|---|---|
| Nickel (Ni) | Balance | 32.0 - 38.0 |
| Chromium (Cr) | 14.5 - 16.5 | 19.0 - 21.0 |
| Molybdenum (Mo) | 15.0 - 17.0 | 2.0 - 3.0 |
| Iron (Fe) | 4.0 - 7.0 | Balance |
| Tungsten (W) | 3.0 - 4.5 | - |
| Cobalt (Co) | ≤ 2.5 | - |
| Manganese (Mn) | ≤ 1.0 | ≤ 2.0 |
| Carbon (C) | ≤ 0.01 | ≤ 0.07 |
| Vanadium (V) | ≤ 0.35 | - |
| Phosphorus (P) | ≤ 0.04 | ≤ 0.045 |
| Sulfur (S) | ≤ 0.03 | ≤ 0.035 |
| Silicon (Si) | ≤ 0.08 | ≤ 1.0 |
| Copper (Cu) | - | 3.0 - 4.0 |
| Niobium (Nb) | - | ≤ 1.0 |
Comparison of corrosion resistance properties between Hastelloy C276 and Monel 400 alloys
| Environment / Condition | Hastelloy C-276 | Alloy 20 |
|---|---|---|
| General Corrosion Resistance | Excellent in both oxidizing and reducing media; outstanding overall corrosion resistance. | Good general corrosion resistance, particularly in sulfuric acid environments. |
| Oxidizing Environments | Excellent resistance (e.g., nitric acid, chromic acid, oxidizing salts). | Good resistance, especially with molybdenum and copper additions enhancing performance. |
| Reducing Environments | Excellent resistance (e.g., hydrochloric acid, dilute sulfuric acid). | Good resistance to sulfuric acid up to moderate concentrations; limited in strong reducing acids. |
| Localized Corrosion (Pitting/Crevice) | Exceptional resistance due to high Mo and Cr content; very high Pitting Resistance Equivalent Number (PREN). | Good resistance, but lower than C-276; suitable for many chloride-containing environments. |
| Stress Corrosion Cracking (SCC) | Excellent resistance to chloride-induced SCC; stable in harsh chloride environments. | Good resistance in many environments, but less resistant than C-276 in severe chloride conditions. |
| Sulfuric Acid | Excellent across a wide range of concentrations and temperatures. | Excellent, especially in medium concentrations and elevated temperatures. |
| Hydrochloric Acid | Excellent, even at elevated temperatures and concentrations. | Limited resistance; not recommended for concentrated or hot HCl. |
| Phosphoric Acid | Excellent performance in most conditions. | Good resistance, widely used in phosphoric acid production. |
| Nitric Acid | Good to excellent resistance; suitable for many applications. | Excellent resistance, often used in nitric acid service. |
| Organic Acids (e.g., acetic, formic) | Excellent resistance. | Good to excellent resistance. |
| Chlorides & Hypochlorites | Outstanding resistance in both acidic and alkaline chloride solutions. | Good resistance in many chloride environments, but not for highly oxidizing chlorides. |
| Wet Chlorine Gas | Excellent resistance; commonly used in bleach and chlorination systems. | Good resistance, often used in similar applications. |
| Seawater & Marine Environments | Excellent resistance to pitting and crevice corrosion. | Good resistance, but less suitable for high-velocity or high-temperature seawater. |
| High-Temperature Stability | Excellent oxidation resistance and thermal stability up to about 1100°C (2012°F). | Limited to lower temperatures compared to C-276; generally up to about 400°C (752°F). |
Corrosion Resistance Comparison
Sulfuric Acid
Alloy 20 is specifically designed for sulfuric acid environments. At moderate temperatures, it performs exceptionally well in sulfuric acid solutions up to approximately 60% concentration. It is a cost-effective solution in applications where sulfuric acid corrosion is the primary concern.
While Hastelloy C276 is resistant to sulfuric acid corrosion, it is not optimized for sulfuric acid environments. In sulfuric acid environments where Alloy 20 is suitable, Hastelloy C276 is generally considered too expensive and over-engineered.
Hydrochloric Acid
Hastelloy C276 is one of the few alloys capable of resisting hydrochloric acid corrosion over a wide range of concentrations and temperatures. Alloy 20 is not recommended for hydrochloric acid environments due to its susceptibility to rapid corrosion.
Chloride Environments
Alloy 20 has good resistance to chloride stress corrosion cracking, but is susceptible to pitting corrosion in high-concentration chloride solutions.
Hastelloy C276 provides excellent resistance to pitting and crevice corrosion, even under highly corrosive chloride conditions.
Mixed Chemical Environments
Alloy 20 is effective in moderately oxidizing and reducing environments, but is not suitable for strong oxidizing agents such as nitric acid.
Hastelloy C276 performs well in both oxidizing and reducing environments, making it a more versatile choice for mixed chemical applications.
Gnee Steel is a professional manufacturer of various nickel-based alloys, including Nickel 201, Nickel 202, Hastelloy C-276, Hastelloy C-22, Hastelloy B, Hastelloy C-4, Inconel Alloy 600, Inconel 625, Inconel 718, Inconel X-750, Incoloy Alloy 800, Incoloy 800H/HT, Incoloy 825, Monel Alloy 400, Monel K500, and high-temperature alloys. We specialize in the production and sales of alloy materials. Gnee Steel's products are widely used in aerospace, chemical, power, automotive, and nuclear energy industries, and we can provide customized alloy material solutions according to customer needs. For alloy material price inquiries or to request customized alloy material solutions, please feel free to contact us at ru@gneesteelgroup.com for a quote.