CORROSION RESISTANCE OF HASTEllOY®AllOYS - Haynes ...

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).
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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.
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