Stainless metallurgy corrosion resistance

The metallurgy of the cyclone equipment has in recent years focused primarily on type 304 H stainless steel. The 304 H material is durable and easy to fabricate and repair, withstands the high regenerator temperatures, and is oxidation- and corrosion-resistant. Essentially all internal surfaces of the cyclone that are subject to erosion are protected with a 2 cm layer of erosion-resistant lining. When installed and cured, most refractory linings are highly resistant to erosion. 

The basic corrosion behaviour of stainless steels is dependent upon the type and quantity of alloying. Chromium is the universally present element but nickel, molybdenum, copper, nitrogen, vanadium, tungsten, titanium and niobium are also used for a variety of reasons. However, all elements can affect metallurgy, and thus mechanical and physical properties, so sometimes desirable corrosion resisting aspects may involve acceptance of less than ideal mechanical properties and vice versa. 

The metallurgy selected for construction of a firewater pump is dependent on the properties of the water source to be used. For fresh water sources (i.e., public water mains), cast iron is normally adequate although bronze internals may be optional. Brackish or sea water utilization will require the use of highly corrosion resistance materials and possibly coatings. Typically specified metals include alloy bronze, monnel, ni-resistant, or duplex stainless steels sometime combined with a corrosion resistant paint or specialized coating. 

Condensing economizers are constructed from inexpensive, but durable, corrosion-resistant materials. Extensive materials testing has been performed for operation in this service, including for coal combustion (Lahtvee, BaU, Razgaitis, and Butcher). The metallurgy for the tube-side liquid is determined by the liquid chemistry requirements (usually water-based liquid) 304 stainless steel is typical. 

Chromium as ferrochromium is used extensively as alloying element in metallurgy to impart corrosion resistance (e.g., tool steels, stainless steels, nickel-based alloys and superalloys). 

Maahn, E, Jensen, S. K., Larsen, R. M., and Mathiesen, T, "Factors Affecting the Corrosion Resistance of Sintered Stainless Steel," Advances in Powder Metallurgy and Particulate Materials, 1994, MPIF, Princeton, NJ, Vol. 7, pp. 253-271. 

Klar, E. and Samal, P. K., "On Some Practical Aspects Related to the Corrosion Resistance of Sintered Stainless Steels, Proceedings of PM 94, Powder Metallurgy World Congress, Paris, 6-9 June 1994, pp. 2109-2112. 

Refinery management, 524-525 Refinery metallurgy, 415-429 metals used in refinery service, 415-416 stainless steel nomenclature, 416-418 corrosion resistance, 417, 419—426 embrittlement dangers, 426 rigorous service, 426-427 heat-exchanger tube fouling, 428 troubleshooting problems, 428... 

Electronic uses of selenium are related to its semiconductor and photoelectric characteristics. Selenium is used in the manufacture of semiconductors, thermoelements, photoelectric and photocells, and xerographic materials. In metallurgy selenium improves the stability and machineability of various allys, is used to color copper alloys, and is added to stainless steel to enhance the corrosion resistance [44]. 

Because alterations to equipment design can be cumbersome and expensive, a more economical approach may be to change the metallurgy of affected components. Metals used in typical cooling water environments vary in their resistance to erosion-corrosion. Listed in approximate order of increasing resistance to erosion-corrosion, these are copper, brass, aluminum brass, cupronickel, steel, low-chromium steel, stainless steel, and titanium. 

Changing the pump metallurgy to a more corrosion- and cavitation-resistant material, such as stainless steel, is a potential solution to this type of problem. Note, however, that all other cast iron pump components that have sustained graphitic corrosion should be replaced to avoid the possibility of galvanic corrosion (see Chap. 16) between retained graphitically corroded cast iron components and new components. 

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