CORROSION RESISTANCE OF HASTEllOY®AllOYS - Haynes ...

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CHLORINE AND HYPOCHLORITES HASTELLOY® alloy C-276 is one of the few metallic materials possessing adequate resistance to chlorine dioxide, hypochlorites, and other solutions containing free chlorine in appreciable concentrations, such as those used for bleaching purposes. However, the alloy may be attacked in solutions above room temperature, especially at temperatures over 150 deg. F (66 deg. C). ~ . Alloy C-276 has been successfully and extensively employed for handling chlorine, both wet and dry, in such parts as valves, piping, vessels, cracking tubes, and feed pipes. It has been used with excellent results in various types of chlorinating equipment, such as are used in swimming pools and city waterpurification units. At room temperature, the rate of penetration in wet chlorine gas is less than one mil (0.03 mm) per year; at higher temperatures, however, local attack may occur. HAYNES® alloy No. 25, a high-temperature alloy, has also shown excellent resistance to wet chlorine gas at room temperature. Tests have shown a penetration rate of less than one mil (0.03 mm) per year in this medium. SALTS Alloys B-2 and C-276 are highly resistant to acid chlorides, such as ammonium or zinc chloride. Alloy C-276 resists acid sulfates, such as aluminum or ammonium sulfate, and acid phosphates. Alloy C possesses unusual resistance at temperatures up to 150 deg. F (66 deg. C) to such strongly corrosive oxidizing salts as solutions of cupric chloride, and ferric and cupric sulfate; and also to mixtures of oxidizing salts, such as chromates and nitrates, in sulfuric or hydrochloric acid. Ferric chloride is one of the most corrosive chemicals likely to be encountered in the field of oxidizing acid salts. HASTELLOY alloy C-276 will resist this salt at room temperature and can be recommended for use with concentrations up to 40 percent at 150 deg. F (66 deg. C). SEAWATER HASTELLOY alloy C-276 has outstanding resistance to seawater, even when it is polluted. Alloy C-276 is used extensively for heat exchangers to cool hot concentrated acid in sulfuric acid plants using seawater as the cooling media because of its resistance to both seawater and sulfuric acid. Corrosion samples of HASTELLOY alloy C, a predecessor of alloy C-276, have been exposed to the sea atmosphere on an Atlantic Ocean beach for over 41 years and still retain their luster and reflectivity. Since alloy C-276 has improved resistance to pitting, crevice corrosion and stress-corrosion cracking, it should have even better resistance than alloy C under similar conditions. LOCALIZED CORROSION The good-to-excellent resistance of HASTELLOY alloys G, G-3, C-276 and CABOT® alloy No. 625 to localized corrosion attack such as pitting, crevice corrosion and stress-corrosion cracking is shown in the tables and charts which follow. 80
EFFECT OF TEMPERATURE ON PITTING RESISTANCE IN A SEVERELY OXIDIZING ENVIRONMENT* 77 DEG. F (25-DEG. C) Type 316L Stainless Steel 20 Cb-3** alloy Alloy 825 HASTELLOY® alloy G Alloy 625 HASTELLOY alloy C-276 1 158 DEG. F (70 DEG. C) (~ , ·2'.. 216 DEG. F (102 DEG. C) *24-hr. exposure in 7 Yol. % H 2S0 4 + 3 Yol. % HCI + 1% CuCI 2 + 1% FeCI 3 •• Trademark of Carpenter Technology Corporation 81
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OUR NEW NAME Haynes International,
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COMPARATIVE CHEMICAL COMPOSITIONS,
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Type 316 Concen- Temperature HASTEL
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Page 63 and 64: ISOCORROSION DIAGRAMS· HASTELLOY®
Page 65 and 66: ISOCORROSION DIAGRAMS* HASTELLOY®
Page 69 and 70: ISOCORROSION DIAGRAMS· r HASTELLOY
Page 71 and 72: PHOSPHORIC ACID ISOCORROSION DIAGRA
Page 75 and 76: ISOCORROSION DIAGRAMS· HASTELLOY®
Page 79: ACETIC AND FORMIC ACIDS Acetic and
Page 83 and 84: CREVICE-CORROSION DATA IN 10% FERRI
Page 85 and 86: CORROSION RESISTANCE OF HAYNES® AL
Page 87 and 88: TYPICAL PENETRATION RATES IN CORROS
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