Corrosion engineering (third edition) part 2
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Corrosion engineering (third edition) part 2
CHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2be the production, use, and effects of sulfuric, nitric, hydrochloric, hydrofluoric, and phosphoric acids. The widespread use of these acids places them in an important position with regard to costs and destruction by corrosion. In some cases corrosion increases with concentration of the acid and in Corrosion engineering (third edition) part 2 others it decreases. For these reasons it is important to have a good picture of corrosion by various acids. Sulfuric, nitric, and hydrochloric acidsCorrosion engineering (third edition) part 2
are the three most important inorganic acids. (Sulfuric and sulfamic acids exhibit about the same corrosive behavior.)SULFURIC ACIDMore sulfuric acidCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2 economy. The consumption rate of sulfuric acid, like steel production or electric power, could be used as a yardstick to judge economic conditions in our nation. The principal uses of sulfuric acid arc for production of hydrochloric acid, other chemicals, and their derivatives: pickling of steel an Corrosion engineering (third edition) part 2d other metals; manufacture of fertilizers, dyes, drugs, pigments, explosives, synthetic detergents, rayon, and other textiles; petroleum refining; stCorrosion engineering (third edition) part 2
orage batteries; metal refining; and production of rubbers. Corrosion problems occur in plants for making the acid and also in consumers' plants when CHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2 for about 70/o of total production. Figure 7-10EconomizerLEGENDC3 Sulfur --------Drying ocidf~1 Air—— Absorbing ocid - Product ocidL--J so2 gos -----OleumCZ3 SOj gosFigure 7-1 Typical contact process for producing sulfuric acid. (General Chemical Co.)MINERAL ACIDS 319show$ schematically a typical c Corrosion engineering (third edition) part 2on tact-process plant. Sulfur, or sulfur compounds such as copper sulfide ore, is burned to form so2, which is converted to so3 in the presence of oxyCorrosion engineering (third edition) part 2
gen and a catalyst. Absorption of this gas by water produces sulfuric acid. Fuming acid (oleum) is made by dissolving so 3 in 100% acid, and these aciCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2either 20% oleum or 104.5% sulfuric acid. Most of the acid produced is shipped to the customer in three concentrations, namely, 78%, 93%, and oleum.7-1 SteelOrdinary carbon steel is widely used for sulfuric acid in concentrations over 70%. Storage tanks, pipelines, tank cars, and shipping drums made Corrosion engineering (third edition) part 2 of steel commonly handle 78%, 93%, 98% acids and oleum. Most of the equipment shown in Fig. 7-1 is made of steel.Figure 7-2 shows corrosion of steelCorrosion engineering (third edition) part 2
by “strong” sulfuric acid as a function of temperature and concentration. More dilute acids attack steel very rapidly. Figure 7-2 is an isocorrosion cCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2ailable to delineate the curves.The curves in Fig. 7-2 represent corrosion rates of 5,20,50, and 200 mpy. These are isocorrosion or constant-corrosion lines. In other words, the outlined areas represent regions where corrosion rates of 0 to 5, 5 to 20. 20 to 50, 50 to 200, and over 200 mpy would be Corrosion engineering (third edition) part 2expected. The corrosion of320 CORROSION ENGINEERINGSteel by strong sulfuric acid is complicated because of the peculiar dips in the curves or the rapiCorrosion engineering (third edition) part 2
d increase in corrosion in the neighborhood of 101% acid. The narrowness of this range means that the acids must be carefully analyzed in order to obtCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2would not be suitable in concentrations below about 65% at any temperature. Above 70% strength, steel can be used, depending on the temperature involved. Steel is generally unsuitable above 175CF at concentrations up to about 100%. Applications involving corrosion rates in the range of 50 to 200 mpy Corrosion engineering (third edition) part 2 would involve relatively short life for steel and should be considered carefully; steel should be used only if economics demands the use of steel inCorrosion engineering (third edition) part 2
spite of fairly frequent replacement. Steel shows comparatively high rates of corrosion around 101% acid. Corrosion data in this region are not plentiCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2more or less conjecture, and additional data are required. The 200-mpy curve stops at 100% acid because one hesitates to guess at the shape of this curve in stronger acids.High-ưe/ơcữy acid would increase corrosion over that shown in Fig. 7-2. For example, steel pumps would not be satisfactory. Few Corrosion engineering (third edition) part 2data are available on the effects of velocity, but it seems safe to say that a few feet per second should not alter the situation. Solids in suspensioCorrosion engineering (third edition) part 2
n may also result in erosion corrosion.Aeration in itself has little effect on corrosion of steel by concentrated acids because they are inherently oxCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2ematurely because of grooving of the top inside surface of the pipe. The groove was very sharp and deep, and the other surfaces of the pipe showed practically no attack. Failure was attributed to air bubbles riding along the top of the pipe. The air was drawn into the system through the packing of t Corrosion engineering (third edition) part 2he pumps moving the acid. This rapid failure of the line was overcome by venting the air or by preventing the air from entering the pump.Occasional faCorrosion engineering (third edition) part 2
ilures have been observed in strong sulfuric acid, and the rapid attack has been attributed to spheroidized pearlite. Normal pearlitic structures showCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2ows the same picture as steel in sulfuric acid. No attempt is made to present an isocorrosion chart for cast iron because the chemical composition of “ordinary” gray irons varies consider-MINERAL ACIDS 321acids, and in very hot and very strong acid it is better than most materials, including stainle Corrosion engineering (third edition) part 2ss high alloys. However, the corrosion rates are high. The better resistance in this case is probably due to the graphite network interfering with theCorrosion engineering (third edition) part 2
reaction between the acid and the metallic matrix.A peculiar phenomenon occurs in oleum, and ordinary gray iron is not generally recommended for thisCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2te flakes, and a little corrosion in these confined areas builds up enough pressure form the corrosion products to split the iron. This is similar to the wedging action described under stress corrosion in Chap. 3. A specimen of gray iron exposed to oleum at room temperature will gain weight. If this Corrosion engineering (third edition) part 2 specimen is washed and dried and then let stand, acid will reappear on the surface. In other words, the metal acts somewhat like a sponge, it is beliCorrosion engineering (third edition) part 2
eved that interconnecting graphite flakes are required for cracking to occur. Malleable and nodular iron or ductile iron should be satisfactory for olCHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describ Corrosion engineering (third edition) part 2ay iron primarily for safety reasons in applications where line breakage would result in acid contact with personnel. Cast iron lines should be W'ell supported because of the brittleness of this material.7-3 Chemical Lead Corrosion engineering (third edition) part 2CHAPTERMINERAL ACIDSMost of the severe corrosion problems encountered involve the mineral acids or their derivatives, in this chapter we shall describGọi ngay
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