Overview of the corrosion resistance of metal materials

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Corrosion resistance of metal materials Category Name Corrosion resistance notes Alloy 316SST, 316LSST are commonly used austenitic stainless steels. Compared with standard 302SST stainless steel, 316SST and 316LSST exhibit better corrosion resistance to sulfuric acid, sulfide solutions, salts of sodium and manganese, hydrochloric acid solutions, and phosphoric acid solutions than 302SST; they also show good corrosion resistance to acetic acid, formic acid, methanol, and hot alkaline solutions. Such steels have a low carbon content, so heat treatment is not required after welding. In particular, 316LSST, which is known as ultra-low carbon stainless steel, has better resistance to intergranular corrosion than 316SST, and therefore exhibits superior corrosion resistance. It is resistant to corrosion by hydrofluoric acid, wet chlorine gas, hydrochloric acid gas, as well as iodine, bromine, etc. Monel alloy is one of the most resistant metals to hydrofluoric acid, aside from platinum and silver. It can also be used as a preservative in chlorides, seawater, and alkalis. It is resistant to nitric acid, hydrochloric acid, and sulfuric acid at high concentrations or in a boiling state, but it is not suitable for use in solutions containing acidic iron salts, tin salts, etc. When a large amount of oxygen enters the medium, hydrofluoric acid, the corrosion resistance decreases; it is also poor in high-concentration sodium hydroxide. Hastelloy C and Hastelloy C-276 possess a much higher corrosion resistance than ordinary austenitic stainless steels. It is suitable for use in mixtures of various corrosive media, and can operate in wet chlorine, dry chlorine, nitric acid (<50°C), hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, hypochlorites, ferric chloride, copper chloride, sodium hydroxide, seawater, and various organic acids. Pure gold and nickel are particularly resistant to corrosion by alkalis; they remain stable in both high temperatures and molten alkalis, which is why they are mainly used in the alkali industry. At room temperature, nickel is highly stable in seawater, saline solutions, and organic media such as fatty acids, phenols, alcohols, etc. It is not resistant to corrosion by inorganic acids, and it is also unstable in acetic acid and formic acid. Titanium is a pure metal with excellent corrosion resistance. It exhibits particularly strong corrosion resistance in various concentrations of nitric acid, organic acids, chlorides, wet chlorine gas, and alkalis. It is not resistant to the corrosion of relatively pure reducing acids and hydrochloric acid. Tantalum is a pure metal with high chemical stability. It exhibits excellent corrosion resistance in many corrosive media, such as inorganic acids, aqua regia, organic acids, chlorides, salts, and corrosive gases. Resistant to corrosion by hydrofluoric acid, fuming sulfuric acid, free sulfur trioxide, potassium iodide, fluoride-containing solutions, and strong alkalis at high temperatures. Note: To improve the mechanical properties of pure metals, trace amounts of other metals are added during the smelting process as needed. Reference table for the corrosion resistance of materials used in parts contacting the medium
Classification | Medium name | Concentration (%) | Temperature
---|---|---|---
Carbon steel | 316 steel | Hastelloy C | Monel | Tantalum | Nickel | Titanium
Inorganic salts | Hydrochloric acid | 5 | RT, BP | ○ | ○ | ○ | ○ | ○ | ● | ● | ○ | ○
Organic salts | Hydrofluoric acid | 5–48 | RT | RT | ○ | ○ | ○ | ○ | ○ | ● | ○ | ○ | 10 | RT, BP | ○ | ○ | ○ | ○ | ● | ● | ○ | ○
Acetic acid | 100 | RT, BP | ○ | ○ | ● | ● | ● | ● | ● | ● | ● | 20 | RT, BP | ○ | ○ | ○ | ○ | ● | ● | ○ | ○ | ○
Formic acid | 50 | RT, BP | ○ | ○ | ○ | ○ | ● | ● | ● | 35 | RT, BP | ○ | ○ | ○ | ○ | ● | ● | ○ | ○ | ○
Oxalic acid | 10 | RT, BP | ○ | ○ | ○ | ● | ● | ○ | ○ | ○
Sulfuric acid | 5 | RT, BP | ● | ○ | ● | ● | ● | ○ | ○ | ○
Citric acid | 50 | RT, BP | ○ | ○ | ● | ● | ● | ● | ● | 10 | RT, BP | ○ | ○ | ● | ○ | ● | ● | ○ | ○ | ○
Alkalis | Sodium hydroxide | 20 | RT, BP | ● | ● | ● | ● | ● | ● | ● | 60 | RT, BP | ○ | ○ | ● | ○ | ● | ● | ○ | ○ | ○
| 40 | RT, BP | ● | ● | ● | ● | ○ | ○ | ● | ● | 80 | RT, BP | ○ | ○ | ○ | ● | ○ | ● | ○ | ○ | ○
| Potassium hydroxide | 50 | BP | ● | ● | ● | ● | ○ | 95 | RT, BP | ○ | ● | ○ | ● | ○ | ● | ○ | ○ | ○ | ○
Salts | Ferric chloride | 30 | RT, BP | ○ | ○ | ○ | ○ | ○ | ● | ● | ○ | ● | ●
Nitric acid | 10 | RT, BP | ○ | ● | ● | ○ | ○ | ● | ● | ○ | ○ | ● | ●
Sodium chloride | 20°, saturated | RT, BP | ● | ○ | ● | ● | ● | ● | ● | 30 | RT, BP | ○ | ● | ● | ○ | ○ | ● | ● | ○ | ● | ○
Ammonium chloride | 25 | RT, BP | ○ | ● | ● | ● | ● | ● | 68 | RT, BP | ○ | ● | ● | ○ | ● | ● | ○ | ○ | ● | ●
Calcium chloride | 25 | RT, BP | ● | ● | ● | ● | ● | ● | Fuming | RT | ● | ○ | ○ | ○
Magnesium chloride | 42 | RT, BP | ● | ● | ● | ● | ● | ● | ● | Phosphoric acid | 30 | RT, BP | ○ | ○ | ● | ● | ○ | ○ | ● | ● | ○ | ○
Sulfides | Sulfuric acid | 20°, saturated | RT, BP | ● | ● | ● | ● | ● | ● | 50 | RT, BP | ○ | ○ | ● | ● | ○ | ○ | ● | ● | ○ | ○
Sodium sulfide | 10 | RT, BP | ● | ● | ● | ● | ● | ● | 70 | RT, BP | ○ | ○ | ● | ○ | ● | ○ | ● | ● | ○ | ○
Sodium sulfate | 50 | RT, BP | ● | ● | ● | 85 | RT, BP | ○ | ○ | ● | ○ | ● | ○ | ● | ● | ○ | ○
Nitrates | *ao acid | 10 | RT, BP | ● | ● | ● | ● | ○ | ● | ● | 35% HCl + 0.5% HNO₃ | RT | ●
Potassium nitrate | All | RT, BP | ● | ● | 90% H₂SO₄ + 10% HNO₃ | RT | ●
Corrosive gases | Chlorine gas | Dry | RT | ● | ● | ● | ○ | 70% H₂SO₄ + 30% HNO₃ | RT | ●
| Wet | RT | ○ | ● | ● | 50% H₂SO₄ + 50% HNO₃ | RT | ●
Chlorinated water | Saturated | RT | ○ | ● | Chromic acid | 20 | RT, BP | ● | ● | ● | ○ | ○
Sulfur dioxide | Wet | RT, BP | ● | ● | Aqua regia | HCl 3, HNO₃ 1 | 1 | RT, BP | ○ | ○ | ● | ○ | ● | ●
Hydrogen sulfide | Wet | RT | ● | ● | ○ | ●

Note: Markings: ● – Excellent corrosion resistance; ○ – Poor corrosion resistance. Symbols: RT – Room temperature; BP – Boiling point.
Material types and remarks: Wetted diaphragm, isolation diaphragm: 316L, Hastelloy C, Monel alloy, Tantalum. 1. Select appropriate materials based on the type and corrosiveness of the medium being handled. 2. Select a material for the liquid-contact diaphragm whose corrosion resistance is as high as possible compared to other parts. Remote control diaphragms: 316L, Hastelloy C, Monel alloy, tantalum, nickel 200, titanium. Exhaust/drain valves: 316, 316L, Hastelloy C, Monel alloy. Chambers and elbow connections: chrome-plated carbon steel, 316, Hastelloy C, Monel alloy. Sealing “O-rings”: fluororubber. Characteristics: excellent resistance to high temperatures and chemical agents. Suitable media: petroleum-based oils, diester-based oils, silicone-based oils, silicones, halogenated hydrocarbons, refined phosphates, strong acids (concentrated phosphoric acid or nitric acid), etc. Operating temperature: –29 to +260°C. Not suitable for use with ammonia-based media. Nitrile rubber. Characteristics: good oil resistance, wear resistance, tear resistance, and low permanent deformation. Suitable media: petroleum-based oils, silicones, lubricating oils, water, ethylene glycol, etc. Operating temperature: –54 to +150°C. EPDM rubber. Characteristics: heat resistance, ozone resistance, resistance to natural aging, resistance to various polar solvents and water vapor. Suitable media: water, water vapor, phosphate ester fluids, moderately strong acids, alkalis, alcohols, polar chemical agents, sulfur hexafluoride, etc. Operating temperature: –54 to +180°C (204°C for water vapor). Neoprene rubber. Characteristics: excellent ozone resistance, weather resistance, oil resistance, and electrical properties. Suitable media: petroleum-based oils, Freon, moderately strong acids, ammonia, and silicone-based lubricants. Operating temperature: –54 to +150°C. Suitable for use in synthetic ammonia systems. Electronic housings: low-copper aluminum alloys, coated with spray paint. “O-rings” on the covers: nitrile rubber. Mounting brackets and fasteners: galvanized carbon steel, 302 stainless steel. Stainless steel should be used in humid and corrosive environments.