Iron-chromium-nickel steels, high-temperature corrosion

High-carbon austenitic structures can be preserved at ambient temperatures if the iron is alloyed with sufficient nickel or manganese, since these metals form solid solutions with 7-Fe but not with a-Fe. If over 11% chromium is also present, we have a typical austenitic stainless steel. Such steels are corrosion resistant, nonmagnetic, and of satisfactory hardness, but, because the a-Fe 7-Fe transition is no longer possible, they cannot be hardened further by heat treatment. Figure 5.9 summarizes these observations. 

Carbon-steel tubes and cast-iron shells are least expensive, but high-sulfur crude oils may justify the use of 5 per cent chromium or even 18-8-chrome nickel tubes" particularly in cracking service. Refer to Chap. 9, pages 276 to 284. For the acid corrosion produced by salt brine, admiralty metal or occasionally cupronickel tubes are justified. Ammonia is often used as a neutralizer for acid corrosion, and it attacks admiralty metal so rapidly that admiralty metal cannot be used for such a situation. The mechanical properties of this alloy are also impaired by temperatures above 500°F, although under favorable conditions it can be used up to tube-wall temperatures of 600 F. Recommendations are as follows ... 

---