Stainless high-temperature corrosion

Ferritic stainless steels depend on chromium for high temperature corrosion resistance. A Cr202 scale may form on an alloy above 600°C when the chromium content is ca 13 wt % (36,37). This scale has excellent protective properties and occurs iu the form of a very thin layer containing up to 2 wt % iron. At chromium contents above 19 wt % the metal loss owiag to oxidation at 950°C is quite small. Such alloys also are quite resistant to attack by water vapor at 600°C (38). Isothermal oxidation resistance for some ferritic stainless steels has been reported after 10,000 h at 815°C (39). Grades 410 and 430, with 11.5—13.5 wt % Cr and 14—18 wt % Cr, respectively, behaved significandy better than type 409 which has a chromium content of 11 wt %. 

M. Fukumoto, C. Tachikawame, Y. Matsuzaka, M. Hara, Formation of Si diffusion layer on stainless steels and their high temperature corrosion resistance in molten salt, Corros. Sci. 56 (2012) 105—113. 

F.J. Perez, E. Otero, M.P. Hierro, C. Gomez, F. de Pedtaza, J.L. Segovia, E. Roman, High temperature corrosion protection of austenitic AISI304 stainless steel by Si, Mo and Ce ion implantation. Surf. Coat. Tech. 108-109 (1998) 127-131. 

IRRAS can be extremely useful for studying in situ the corrosion and anticorrosion mechanisms [295]. For example, in order to understand high-temperature corrosion processes on AISI type 304 stainless steel, Guillamet et al. [284] measured the spectra by IRRAS of a steel plate exposed for 1 min to air at high temperatures. Comparison with the vlo bands of a series of oxides indicated that the main product is a-Fc203 (not Fc304, as suggested earlier for corrosion of... 

Characterisation of the High Temperature Corrosion Behaviour of the Modified 9Cr-l Mo Steel Conference Process 6 Materials Irmovation Stainless Steel. Vol. 3, Florence, Italy, 11—14 Oct.1993 Assoziatione ItaUana di Metallurgia, Milano, Italien, 1993 S. 3.133-3.138 [6 Ozaki, T Ishikawa, Y... 

Johansson, R., J. Hamer, J. Redmond and R.M. Davison, 1990, Oxidation and high-temperature corrosion resistance of REM treated stainless steels (Corrosion 90, NaCE) Paper 294. 

Chromium. Chromium is, of course, the primary element for forming the passive film or high-temperature, corrosion-resistant chromium oxide. Other elements can influence the effectiveness of chromium in forming or maintaining the film, but no other element can, by itself, create the stainless characteristics of stainless steel. The passive film is observed at about 10.5% chromium, but it affords only limited atmospheric protection at this point. As chromium content is increased, the corrosion protection increases. When the chromium level reaches the 25 to 30% level, the passivity of the protective film is very high, and the high-temperature oxidation resistance is maximized. 

Mrowec S, New generation of nanocrystaUine coating materials resistant to high temperature corrosion , High Temp Mater Proc, 2003, 22(1), 1-24 Peng X, Yan J, Zhou Y, Wang F, Effect of grain refinement on the resistance of 304 stainless steel to breakaway oxidation in wet air , Acta Mater, 2005, 53(19), 5079-... 

Weak Acid. Stainless steels (SS) have exceUent corrosion resistance to weak nitric acid and are the primary materials of constmction for a weak acid process. Low carbon stainless steels are preferred because of their resistance to corrosion at weld points. However, higher grade materials of constmction are required for certain sections of the weak acid process. These are limited to high temperature areas around the gau2e (ca 900°G) and to places in which contact with hot Hquid nitric acid is likely to be experienced (the cooler condenser and tail gas preheater). 

The fifth component is the stmcture, a material selected for weak absorption for neutrons, and having adequate strength and resistance to corrosion. In thermal reactors, uranium oxide pellets are held and supported by metal tubes, called the cladding. The cladding is composed of zirconium, in the form of an alloy called Zircaloy. Some early reactors used aluminum fast reactors use stainless steel. Additional hardware is required to hold the bundles of fuel rods within a fuel assembly and to support the assembhes that are inserted and removed from the reactor core. Stainless steel is commonly used for such hardware. If the reactor is operated at high temperature and pressure, a thick-walled steel reactor vessel is needed. 

Fatty acids are corrosive at high temperatures and selection of materials of constmction for distillation systems is critical. Stainless steels with various contents of molybdenum have proved satisfactory. For example, 316 L has 2% Mo and is satisfactory for service up to 260°C 317 L has 3% Mo and can be used satisfactorily up to 285°C, whereas 904 L can be used up to 310°C (31). 

Nickel and Nickel Alloys A wide range of ferrous and nonfer-rous nickel and nickel-bearing alloys are available. They are usually selected because of their improved resistance to chemical attack or their superior resistance to the effects of high temperature. In general terms their cost and corrosion resistance are somewhat a func tion of their nickel content. The 300 Series stainless steels are the most generally used. Some other frequently used alloys are hsted in Table 10-35 together with their nominal compositions. For metallurgical and corrosion resistance data, see Sec. 28. 

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