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Ferritic, martensitic and duplex stainless steels tend to become brittle as the temperature is reduced, in a similar way to other ferritic / martensitic steels. The austenitics stainless steels such as 304, (1.4301), and 316, (1.4401), are however ‘tough’ at cryogenic temperatures and can be classed a ‘cryogenic steels’. The toughness of the austenitics relies on their fcc atomic structure. Ferrite or martensite phases in austenitic weld metal or castings can affect the suitability for cryogenic applications. Charpy impact tests are done to assess the toughness of materials.
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The austenitic stainless steels are impact tough at ‘cryogenic’ temperatures compared to carbon steels and so are suitable for handling and storage of liquid ammonia at temperatures around -40 deg. C. The general corrosion resistance of the 304 types should be adequate for installations at most sites, but for coastal or marine sites 316 types should be considered if the outer-casings or parts are exposed.
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Dry chlorine gas should not attack stainless steels. Damp gas or chlorine dissolved in water can be a corrosion hazard. Corrosion can take the form of localised crevice and pitting corrosion. Stress corrosion cracking, (SCC), can be an additional hazard in damp chlorine gas, if the temperature is high enough.
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Dry or liquefied sulphur dioxide gas should not be aggressive towards stainless steels. When dissolved in water it forms sulphurous acid H2SO3 and is mildly corrosive. Oxidation of the acid to sulphuric acid can be a corrosion risk to stainless steels.
