Anhydrous environment, corrosion

Figure 13. Corrosion behavior of reduction reactor materials samples in anhydrous environment (O), Hastelloy C276 Cartech CB3 (V), Incoloy 825 (A), Inconel 625 (O), SS 310 and (0), SS 18-18-2. Furnace temperature, 482°C (900°F) anhydrous S03 12 cc/min argon 128 cc/min. Erratic erosion rate behavior of SS 310 and Cartech 20CB3 is caused by the spalling of the corrosion product. Negative values indicate weight gain per unit area.

Titanium generally shows good corrosion resistance to organic compounds. Many organic compounds are absorbed on titanium surfaces and act as inhibitors. When the temperature is high in an anhydrous environment and the organic compound dissociates, hydrogen embrittlement of the titanium is a consideration. 

Stress-corrosion cracking (Section 8.10) New metal/environment combinations which produce stress-corrosion cracking are continually being found. Combinations discovered in service in recent years include titanium in red fuming nitric acid carbon steel in liquid anhydrous ammonia and in... 

Ammonia is found in the environment as the result of natural and industrial processes. It is released into the environment by the breakdown of organic wastes, and it is a constituent of the soil, the atmosphere, and bodies of water. Ammonia is also a key intermediate in the nitrogen cycle and is a product of amino acid metabolism (WHO 1986). Anhydrous ammonia is used in the production of nitric acid, explosives, synthetic fibers, and fertilizers (Budavari 1989). It is used as a refrigerant as a corrosion inhibitor in the purification of water supplies in steel production as a catalyst for polymers as a preservative for latex and in the production of nitrocellulose, urea formaldehyde, sulfite cooking liquors, and nitroparaffins (ACGIH 1991 Lewis 1993). Ammonium hydroxide (10-35% ammonia) is a major constituent of many cleaning solutions. Ammonia... 

Above 816°C, diffusion of the nitride into titanium may cause embrittlement. Nevertheless, titanium is not corroded by liquid anhydrous ammonia at room temperature. Low corrosion rates are obtained at 40°C. Titanium also resists gaseous ammonia. However, at temperatures above 150°C, ammonia will decompose and form hydrogen and nitrogen. Under these circumstances, titanium could absorb hydrogen and become embrittled. The high corrosion rate experienced by titanium in the ammonia-steam environment at 220°C is believed to be associated with hydriding. The formation of ammonium chloride scale could result in crevice corrosion of Timetal 50A at boiling temperatures. Timetal Code-12 and 50A Pd are totally resistant under these conditions. This crevice corrosion behavior is similar to that shown for sodium chloride. 

Methanol is a clear, colorless, and volatile liquid, giving off a mild alcoholic odor at room temperature. It is polar, acid-base neutral, and generally considered non-corrosive. It is miscible with water and most organic solvents and is capable of dissolving many inorganic salts. Anhydrous methanol is hygroscopic. Methanol is toxic to human beings but is not considered particularly harmful to the environment. 

The first step in material selection is a thorough review of the corrosive environment, process parameters, and equipment operating conditions, including temperature, pressure, flow rates, liquid versus gaseous phase, aqueous verses anhydrous phase, continuous verses intermittent operation, media used for cooling or heating, etc. 

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