Steel corrosion mechanism

Key words landing gear, steel, corrosion mechanism, titanium alloy. 

Amine-Acid Gas Carbon Steel Corrosion Mechanisms... 

Attack at welds due to bacteria is possible, but it is not nearly so common as is often supposed. Because of residual stresses, microstruc-tural irregularities, compositional variation, and surface irregularities, welds show a predisposition to corrode preferentially by most corrosion mechanisms. Attack is common along incompletely closed weld seams such as at butt welds in light-gauge stainless steel tubing (Fig. 6.9A and B). Attack at carbon steel welds may occur. Figure 6.10 shows a severely corroded carbon steel pipe from a service water sys-... 

Rhodes, P. R., Mechanism of Chloride Stress-corrosion Cracking of Austenitic Stainless Steel , Corrosion, 25, 462 (1969)... 

In plain tinplate cans for acid foods, tin provides cathodic protection to steel (3,4). The slow dissolution of tin prevents steel corrosion. Many investigators (5-1I) have defined this mechanism in detail and have shown that the tin dissolution rate is a function of the cathodic activity of the base steel, the steel area exposed through the tin and the tin-iron alloy layers, and the stannous ion concentration. Kamm et al. showed that control of the growth of the tin—iron alloy layer provides a nearly continuous tin-iron alloy layer and improves the corrosion resistance of heavily coated (over 45 X 10"6 in. tin) ETP for mildly acid food products in which tin provides cathodic protection to steel (12). The controlled tin-iron alloy layer reduces the area of steel exposed to the product. ETP with the controlled alloy is designated type K, and since 1964, 75 type K ETP has been used to provide the same protection as 100 ETP provided previously (13). 

The corrosion of steel and other metals in a boiler system takes place when an electrochemical cell is established, although the rates of corrosion and the types of corrosion mechanisms involved are highly dependent on the particular circumstances that develop during the operation of individual boiler plants. A failure to adequately control corrosion ultimately leads to the failure of boiler surface components or other components and items of equipment in the system. 

Electrochemical techniques have been utilized for many years to study metal corrosion. Two of these techniques, linear polarization (LP) and cyclic voltammetry (CV), complement each other, LP providing corrosion rates under conditions where the surface is minimally altered and CV furnishing information about the corrosion mechanism. With the advent of impedance spectroscopy (IS), both kinds of information can be gleaned simultaneously and more rapidly, while leaving the surface almost intact. In this paper, we discuss the application of IS to the study of rapid steel corrosion and describe a study we undertook to elucidate the roles played by adsorption and film formation in the inhibition mechanisms of the above-named compounds. For comparison, we also investigated two quaternary nitrogen salts, which appear to adsorb electrostatically and presumably do not form macroscopic films (8). 

The mechanism of steel corrosion in acid solutions, however, is different from that in neutral solutions in that the reduction reaction is the formation of hydrogen from hydrogen ion ... 

Because of this difference in corrosion mechanism in acid solution, the usefulness of the four evaluation techniques discussed above may be different than in neutral solutions. The purpose of this work was to evaluate these four techniques for predicting the behavior of coating resins in acid solutions. In addition, the ability of several different types of coating resins to protect steel against corrosion in acid solution was evaluated. 

Miyoshi, Y. Kitayama, M. Mishimura, K. Naito, S. "Cosmetic Corrosion Mechanism of Zinc and Zinc Alloy Coated Steel Sheet for... 

Misawa,T Asami, K Hashimoto, K. Shimo-daira, S. (1974 a) The mechanism of atmospheric rusting and the protective amorphous rust on low alloy steel. Corrosion Sci. 14 279-289... 

Misawa, T. Kyuno, T. Suetaka, W. Shimodaira, S. (1971) Mechanism of atmospheric rusting and the effect of copper and phosphorus on the rust formation of low alloy steels. Corrosion Sci. 11 35-48... 

Stainless steel generally withstands polluted sea water and polluted brackish water better than copper-base alloys. Substituting an austenitic stainless screen for silicon-bronze trash racks has resulted in greatly improved service at a west coast power plant. Normally stainless steel screens, because of the crevices involved (where the wires cross), are not recommended for use in sea water. This alteration of the usual corrosion mechanism, presumably related to the hydrogen sulfide content of polluted sea water, needs to be studied. 

In situ Raman spectroscopy is being used to investigate corrosion products from zinc in a humid atmosphere and sodium chloride70 and from Type 304L stainless steel in aerated water at elevated temperatures and pressures.71 The changes in detected species over time helped identify possible corrosion mechanisms and the effect of different variables on corrosion rates and mechanisms. 

Exceptions can exist since the corrosion in a wet solution of the interior boiler drum (steel) with dilute caustic soda at high temperature and high pressure and the reaction of high temperature water with aluminum and zirconium have been found to be best interpreted in terms of a dry corrosion mechanism.1... 

Smith, F.N., C.P. Cutler, D.J. Cochrane, Stainless Steel Reinforcing Bars, Proceedings, Conference on Understanding Corrosion Mechanisms in Concrete, Massachusetts Institute of Technology, Cambridge, MA, July 1997. 

Since steel is the main structural material for bridges, buildings, and automobiles, controlling its corrosion is extremely important. To do so, we must understand the corrosion mechanism. Instead of being a direct oxidation process, as we might expect, the corrosion of iron is an electrochemical reaction, as illustrated in Fig. 11.17. 

A. Carnot, I. Frateur, S. Zanna, B. Tribollet, I. Dubois-Brugger, and P. Marcus, "Corrosion Mechanisms of Steel Concrete Moulds in Contact with a Demoulding Agent Studied by EIS and XPS," Corrosion Science, 45 (2003) 2513-2524. 

Cruz, R.P., Nishikata A., Tsum T., Pitting corrosion mechanism of stainless steel under wet- dry exposure in chloride containing environments, corrosion science, 40, pp 125-139, 1998. 

Weathering steel corrosion can be described as competing mechanisms of formation and dissolution of a protective oxide layer during periods of wetness. 

Gallagher, J. P., and Wei, R. P., Corrosion Fatigue Crack Propagation Behavior in Steels, Corrosion Fatigue Chemistry, Mechanics and Microstructure, NACE-2 (1972), 409. 

For materials like stainless steels, the mechanisms are quite different. Corrosion resistance in stainless steels is provided by a passive film that acts as a barrier between the alloy and the water. The passive film is a continuous, non-porous and insoluble film, which, if broken under normal conditions, is self-healing. Due to these characteristics, the uniform corrosion of stainless steels is usually very low and the major risk is pitting corrosion. The pitting corrosion risk of stainless steels is influenced not only ly the composition of the alloy and by water quality but also by service conditions, quality of the material and quality of the installation (fitting, soldering conditions, etc.). 

Many factors contribute to the corrosion resistance of a modern painted steel or aluminum product including the nature of organic coating, the metal substrate and/or metal coating, and the conversion layer. It is impossible to speak of the corrosion resistance afforded by the conversion layer without reference to the total product. In this section, we will briefly describe some phenomena unique to the conversion layer, which do contribute to the corrosion resistance. A detailed description of corrosion mechanisms under paint is given in Chapter 5.4. 

The situation changes when the defect is prepared just down to zinc and the kinehcs of zinc dissolution are rather slow. In this case, the cathodic delamination determines the kinetics of undermining. The delaminated area of the phosphated sample is now smaller than for the defect down to steel, whereas the just alkaline cleaned sample shows delamination that is much faster than in the case of the defect down to steel. This example shows how complex the corrosion mechanisms are and that no generally accepted mechanism can be found in the literature. 

Regarding molten chlorides, mainly KCl-ZnCl2 mixtures are present in the ashes and fast corrosion occurs at relatively low temperatures. Figure 21 presents results of a thermogravimetric measurement on 2.25Cr-lMo-steel beneath a molten 50 wt. % KCl-50 wt. % ZnCl2 mixture at different temperatures in He-5 vol.% O2 gas mixture. At 350 °C, significant corrosion occurs by the molten salt. The main corrosion mechanism is the dissolution of... 

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