Stress is a requirement for SCC or fatigue, but can also inuence the rate of general corrosion. 3, 9th ed., Metals Park, OH: ASM International, pp. There are two basic pure nickel alloys, each containing a minimum of 99% nickel: alloy 200 and alloy 201. Many environments do not cause intergranular corrosion in sensitized austenitic stainless steels. In the 1970s, this problem was made manageable through the use of nitrogen as an alloy addition. 2004. Formation of aqueous layer. However, stagnant conditions are to be avoided when possible because they are exactly where the various forms of localized corrosion become serious, including pitting, oxygen concentration cells, and microbiologically inuenced corrosion (MIC). For applications above this temperature, alloy 201 should be used. The superferritic materials alloyed with nickel exhibit improved mechanical toughness and are less sensitive to contamination from interstitial elements. TABLE 13.1 Chemical Composition of Alloy PH-13-8Mo (S13800) Chemical Carbon Manganese Phosphorus Sulfur Silicon Chromium Nickel Molybdenum Aluminum Nitrogen Iron Weight Percent 0.05 0.10 0.010 0.008 0.10 12.513.25 7.58.50 2.002.50 0.901.35 0.010 Balance 8243CHAPTER 133/11/200617:14BSARAVANAN14193XML MODEL B pp. Stainless steels are iron-based alloys containing 10.5% or more chromium. Ferritic materials that contain more than about 18% chromium are also susceptible to an embrittlement phenomenon when exposed to temperatures in the range of 60011008F. 99108 100 Fundamentals of Metallic Corrosion: Atmospheric and Media Corrosion of Metals TABLE 5.1 Ferritic Stainless Steels AISI Type UNS Designation AISI Type UNS Designation S40500 S40900 S42900 S43000 S43020 S43023 S43400 S43600 S44200 446 439 444 26-1 26-3-3 29-4 29-4C 29-4-2 S44600 S43035 S44400 S44627 S44660 S44700 S44735 S44800 405 409 429 430 430F 430FSe 434 436 442 Numbering System and the Unied Numbering System (UNS) that were developed by ASTM and SAE to apply to all commercial metals and alloys, dene specic alloy compositions. Carbon plus nitrogen contents were maintained at levels below 0.02%. Corrosion Resistance Tables, Vols. Resistance to intergranular attack in boiling 65% nitric acid and in ferric sulfatesulfuric acid is excellent for both the annealed and sensitized conditions. Alloy 400 exhibits excellent resistance to hydrouoric acid solutions at all concentrations and temperatures, as shown in Figure 15.1. This will go a long way towards reducing or preventing iron embedment. 2. Metabolism can take place within that range. The Fe2 O3 layer is responsible for the passivity, while the Fe3O4 provides the basis for the formation of a higher oxidizing state. Under normal circumstances, this lm will form immediately upon exposure to oxygen. Alloy 20Cb3 is weldable, machinable, and cold formable, and has minimum carbide precipitation due to welding. They are also resistant to many gases provided the moisture content is below the saturation point. The CCT of an alloy is that temperature at which crevice corrosion is rst observed when immersed in a ferric chloride solution. This limits the distance that the SO2 may be transported to a few hundred kilometers. In petroleum process streams, this problem is promoted by so-called hydrogen evolution poisons such as suldes, arsenic compounds, cyanides, and phosphorus-containing ions. Typically, these alloys have carbon contents of approximately 1.84% and silicon contents of 0.53%. Documentation of this class of steel began to appear in the 1920s. The principle of precipitation hardening is that a supercooled solid solution (solutionannealed) changes its metallurgical structure on aging. During this time, Fe3O4 layer continues to form. Schweitzer. A former contract manager and material specialist for Chem-Pro Corporation, Faireld, New Jersey, he is the editor of the Corrosion Engineering Handbook and the Corrosion and Corrosion Protection Handbook, Second Edition; and the author of Corrosion Resistance Tables, Fifth Edition; Encyclopedia of Corrosion Technology, Second Edition; Metallic Materials; Corrosion Resistant Linings and Coatings; Atmospheric Degradation and Corrosion Control; What Every Engineer Should Know About Corrosion; Corrosion Resistance of Elastomers; Corrosion Resistant Piping Systems; Mechanical and Corrosion Resistant Properties of Plastics and Elastomers (all titles Marcel Dekker, Inc.); and Paint and Coatings, Applications and Corrosion Resistance (Taylor & Francis). a b Resistance applies to Duriron unless otherwise noted. Schweitzer received the BChE degree (1950) from Polytechnic University (formerly Polytechnic Institute of Brooklyn), Brooklyn, New York. Chromium is enriched in the inner rust layer, together with copper and phosphorus. 133 8243CHAPTER 83/11/200617:06BSARAVANAN14188XML MODEL B pp. Depending upon the particular corrodent being handled, the effect of carbide precipitation may or may not present a problem. 177195 190 Fundamentals of Metallic Corrosion: Atmospheric and Media Corrosion of Metals TABLE 11.5 Continued Maximum Temperature Chemical 8F 8C Sulfuric acid, 50%a Sulfuric acid, 70%a Sulfuric acid, 90%a Sulfuric acid, 98%a Sulfuric acid, 100%a Sulfuric acid, fuming Sulfurous acida Zinc chloride, 5% 210 150 180 220 230 99 66 82 104 110 370 140 X 188 60 The chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. When rst formed, the patina exhibits a dark color that gradually turns green. In this case, the dry deposition velocity if dependent on the aerodynamic processes. Erosion corrosion 7. This, however, will be ineffectual if the bacteria have previously formed protective nodules as their habitat.

1.1.8.1 Corrosion of Specic Materials Microbially induced corrosion (MIC) may occur for metallic materials in many industrial applications. Stainless steels of all grades, in general, are resistant to erosion corrosion. For many years, cobalt-based superalloys held the edge, but because of the precarious availability of cobalt from South Africa, the nickel-based superalloys have replaced many of the cobalt-based alloys. Calcium hypochlorite Calcium nitrate Calcium oxide Calcium sulfate Caprylic acid Carbon bisulde Carbon dioxide, dry Carbon dioxide, wet Carbon disulde Carbon monoxide Carbon tetrachloride Carbonic acid Cellosolve Chloracetic acid, 50% water Chloracetic acid Chlorine gas, dry Chlorine gas, wet Chlorine, liquid Chlorobenzene Chloroform 8F 8C 80 27 80 80 120 210 90 90 80 90 90 80 27 27 49 99 32 32 27 32 32 27 80 X 27 80 27 80 80 27 27 90 80 210 X 32 27 99 200 80 93 27 80 90 210 570 80 27 32 99 299 27 210 80 80 80 90 99 27 27 27 32 80 90 27 32 (continued) 8243CHAPTER 43/11/200616:57TRGANESH14184XML MODEL B pp. Dew may also form when metal products are brought into warm storage after cold transport. It has limited use in hydrochloric or hydrouoric acids. The foundation for the development of this class of materials was in the development of Carpenter No. 8398 98 Fundamentals of Metallic Corrosion: Atmospheric and Media Corrosion of Metals 6. However, the degree to which these pollutants will affect the corrosion rate will be inuenced by the other preceding factors that also have an inuence on the corrosion rate. The nature of the environment seems to have a greater effect in determining the type of attack. The exact nature of the oxyhydroxide formed seems to have only a minor inuence on the water adsorption phenomena. The FeCr phase diagram suggests that the maximum chromium content would be about 12.7%. It resists suldation, internal oxidation, scaling, and carburization. A single-step aging treatment develops exceptionally high yield strength with good ductility and toughness. Oleum 8F 8C 210 80 210 80 99 27 99 27 210 210 160 100 80 210 210 210 470 210 200 120 80 120 210 200 200 210 190 170 80 80 100 X 99 99 71 X X 38 27 99 99 X X 99 X 243 X X X X X X 99 X X X X X 93 49 27 X 49 X 99 93 93 X 99 88 77 27 27 38 (continued) 8243CHAPTER 103/11/200617:05CRCPAG14190XML MODEL B pp. In continuous service, type 430 may be operated to a maximum temperature of 15008F (8158C) and 16008F (8708C) in intermittent service. They also have excellent resistance to phosphoric, dilute sulfuric, and many other acids and salts. Anodic polarization studies, such as the examples in Figure 10.1, can be useful in understanding the benets of different alloy additions. Type 430 nds wide application in nitric acid plants. The semiaustenitic stainless steels are supplied as an unstable austenitic, which is the workable condition, and must be transformed to martensite before aging. SCC may develop at lower temperatures if the pH is low. 8243CHAPTER 13/11/200616:52TRGANESH14181XML MODEL B pp. In sufcient amounts, however, copper will reduce the pitting resistance of some alloys. It is resistant to SCC in sulfuric acid at a variety of temperatures and concentrations. Corrosion rates are expressed using a time dimension. Vessels and tanks should be designed to provide complete drainage, thereby preventing the buildup of solid deposits on the bottom. 1993. Reference 1. 221234 230 Fundamentals of Metallic Corrosion: Atmospheric and Media Corrosion of Metals have even been classied as nickel alloys. As a general rule, the higher the PREN, the better resistance to pitting. 151176 156 Fundamentals of Metallic Corrosion: Atmospheric and Media Corrosion of Metals 1000 Time to failure 100 10 1 0 10 20 30 40 50 Weight percent nickel FIGURE 10.3 Chloride stress cracking vs. nickel content. If the ller metal will not tolerate striking of an arc, then the arc must be struck adjacent to it, in it, or near the heat-affected zone when it is necessary to strike an arc between runout tabs. Consequently, nickel alloy 200 is limited to a maximum operating temperature of 6008F (3158C). Sodium sulde, to 50% Stannic chloride Stannous chloride Sulfuric acid, 10% Sulfuric acid, 50% Sulfuric acid, 70% Sulfuric acid, 90% Sulfuric acid, 98% Sulfuric acid, 100% Sulfuric acid, fuming Sulfurous acid Thionyl chloride Toluene Trichloroacetic acid White liquor Zinc chloride 8F 8C 180 186 150 80 82 86 66 27 80 80 100 210 80 100 80 150 170 60 90 212 295 386 485 538 644 X X X X X 27 27 38 99 27 38 27 66 77 16 32 100 146 197 252 281 340 X 80 27 The chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. The rate of corrosion is extremely slow but will increase as the SO2 content of the atmosphere increases. The absence of nickel reduces the cost. If this resistant, or passive, layer is damaged while in the aggressive environment, active corrosion of the freshly exposed surface will occur. 151176 Austenitic Stainless Steel Family Carbon Manganese Phosphorus Sulfur Silicon Chromium Nickel Molybdenum Columbium Vanadium Nitrogen Iron 157 0.06 4.00/6.00% 0.040% 0.030% 1.00% 20.50/23.50% 11.50/13.50% 1.50/3.00% 0.10/0.30% 0.10/0.30% 0.20/0.40% Balance It is superior in corrosion resistance to type 316 stainless steel with twice the yield strength; it can be welded, machined, and cold-worked using the same equipment and methods used for the conventional 300-series stainless steels. Values between 1000 and 2700 h/year are often reported from sites in the temperate climatic zone. These solutions should be prepared using demineralized water. The majority of such molecules will form hydrogen bubbles and oat away harmlessly. Table 9.9 shows the chemical composition. The oxygen atom bonds to the metal surface and acts as a Lewis base (donating an electron pair) because the bonding is connected with a net charge transfer from the water molecule to the surface. CF3 and CF8 are the cast equivalents of 304L and 304, respectively. An example of such an attack is that of halogens, particularly chlorides. Page iii The chemical composition is shown in Table 13.2. Table 14.2 gives examples. 8. 8243CHAPTER 143/11/200617:08CRCPAG14194XML MODEL B pp.

Figure 2.1 is a schematic illustration of processes occurring at the aqueous layer. With relatively minor changes within the system, the corrosion current could be very low when the material is in the passive state or very high when active corrosion begins. Weathering steels that contain small additions of copper, chromium, and nickel to form a more adherent oxide during atmospheric exposures. The application of antifouling paints is probably the most effective and most widely used means of preventing biofouling in seawater. As with other CTX alloys, a protective coating is required if the alloy is exposed to atmospheric conditions above 10008F (5388C). The critical relative humidity varies for different metals and pollutants. Excellent stress corrosion resistance has been exhibited by this 8243CHAPTER 133/11/200617:14BSARAVANAN14193XML MODEL B pp. The problem is rarely encountered because the alloys are supplied in the annealed condition and the service temperatures rarely approach the level required for sensitization. Calcium hypochlorite Calcium nitrate Calcium oxide Calcium sulfate Caprylic acidb Carbon bisulde Carbon dioxide, dry Carbon dioxide, wet Carbon disulde Carbon monoxide Carbon tetrachloride Carbonic acid Cellosolve Chloracetic acid, 50% water Chloracetic acid Chlorine gas, dry Chlorine gas, wet Chlorine, liquida Chlorobenzene Chloroformb Chlorosulfonic acid Chromic acid, 10% Chromic acid, 50% Chromyl chloride 210 210 210 230 210 400 90 210 150 400 99 99 99 110 99 204 32 99 66 204 180 80 200 210 180 300 210 210 80 210 200 90 90 210 210 210 210 200 210 570 210 210 210 110 210 210 200 90 210 X X X 82 27 93 99 82 149 99 99 27 99 93 X 32 32 99 99 99 99 93 99 299 99 99 99 X X X X 43 99 99 X 93 32 99 (continued) 8243CHAPTER 103/11/200617:05CRCPAG14190XML MODEL B pp. The burning of fossil fuels generates a large amount of sulfur dioxide that is converted to sulfuric and sulfurous acid in the presence of moisture. Excellent resistance is shown to oxidizing chlorides, reducing solutions, and seawater corrosion. Intergranular corrosion is not a problem because the alloy is produced to a low carbon specication and water-quenched from solution annealing, which prevents the formation of any harmful precipitates and eliminates the risk of intergranular corrosion. Halogens form lms on stainless alloys, but their efciency is limited because of the high volatility of metal chlorides. Other sources of chloride emission are coal burning and municipal 8243CHAPTER 23/11/200616:54TRGANESH14182XML MODEL B pp. Phosphorus may form layers of insoluble phosphates in the rust, acting as transportation barriers in the same manner as the basic sulfates previously mentioned. The alloy exhibits a low and relatively constant coefcient of thermal expansion over a broad temperature range, a high hot hardness, and good thermal fatigue resistance. In addition to the UNS designations previously described, there is also a series of UNS designations specically for cast materials. 9.2 Type 414 (S41400) Type 414 stainless steel is a nickel-bearing chromium stainless steel. Applications have included furnance parts, kiln linings, and annealing boxes. Schweitzer. 3966 Atmospheric Corrosion 41 vicinity of the emission source, the contents of HNO3 and nitrates are very low. Graphite is essentially an inert material and is cathodic to iron. The metal chloride formed hydrolyzes to produce metal hydroxide and hydrochloric acid: MCl C H2 O/ MOH C HCl The nascent hydrochloric acid destroys the passive lm and accelerates the rate of dissolution of the metal inside the crevice. 1.1 Forms of Corrosion There are nine basic forms of corrosion that metallic materials may be subject to: 1. Source: From P. A. Schweitzer. OHK is generated by photoinduced dissociation of O3 (ozone) and the subsequent reaction of the electronically excited, energy-rich oxygen atom O ( 0 D) and water vapor: O3 C hn/ O 0 D C O2 l! Acids or bases with tightly held valence electrons that are not easily distorted are hard acids or bases. This type of attack takes place in certain media. In strongly oxidizing environments, the lower molybdenum of CF8 provides superior corrosion resistance. Fatigue is triggered by a tensile stress that must approach the yield stress of the metal. Table 305 stainless steel has the equivalent corrosion resistance of type 304 stainless steel. For many materials, the stress range required to cause fatigue failure diminishes progressively with increasing time and with the number of cycles of applied stress. The compositions of many cast grades are modied relative to their wrought equivalents to take advantage of the casting process because little or no mechanical working of the cast component will be necessary. However, when exposed in a seacoast atmosphere it will gradually develop overall light rusting and pitting in all heat-treated conditions. 2004. By setting the standard chemical potential of the solvated proton and of the molecular hydrogen equal to zero, m0HC Z 0; m0H2 Z 0, it is possible to dene the standard potential of the partial reduction reaction of Equation (1.10) with respect to the standard hydrogen electrode.

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