Corrosion alloys, selective

Alloy selection is not made fiom only consideration of strength and conductivity. For example, the cupronickels have about the same strength as do copper—2inc brasses, and also have much lower conductivity. However, the corrosion resistance of the cupronickels far exceeds that of brass and is worth the higher cost if needed in the appHcation. Similar trade-offs exist between these properties and formabiUty, softening resistance, and other properties. 

Certain types of corrosion are selective. Thus, corrosion cracking is observed primarily in the case of alloys and only when these are in contact with particular media. Corrosion is often enhanced by various extraneous effects. Stress corrosion cracking can occur under appreciable mechanical loads or internal stresses corrosion fatigue develops under prolonged cyclic mechanical loads (i.e., loads alternating in sign). 

T. A. Danielson, Corrosion of Selected Alloys in Sub-and Supercritical Water Oxidation Environments, Thesis, University of Texas USA, (1995). 

Properties. Most of the alloys developed to date were intended for service as fuel cladding and other structural components in liquid-metal-cooled fast-breeder reactors. Alloy selection was based primarily on the following criteria corrosion resistance in liquid metals, including lithium, sodium, and NaK, and a mixture of sodium and potassium strength ductility, including fabricabiUty and neutron considerations, including low absorption of fast neutrons as well as irradiation embrittlement and dimensional-variation effects. Alloys of greatest interest include V 80, Cr 15, Ti 5... 

The selection of an alloy for a specific application is based on the cost and the corrosion resistance of the alloy in the environment of interest. It is also possible to subject the chosen alloy to a process by which the corrosion resistance of the selected material can be improved within the acceptable limits. Some of the corrosion prevention and protection strategies with respect to the aluminum-based alloys are (i) design (ii) alloy selection and joint sealants (iii) aluminum thermal spraying anodic coatings (iv) inhibitors (v) conversion and organic coatings and (vi) cathodic protection. 

Prevention of General Corrosion. Proper selection of materials. In design, a metal or alloy that forms a stable passive film should be recommended. A surface pretreatment in oxidized solutions has been adopted for stainless steels and is recommended in many circumstances. The most popular process a 300 min immersion in a 20 vol% nitric acid at 50°C is recommended for some types of stainless steels.21 The environment can be modified in the bulk and should be effective at the interface in adding oxidizing agents, such as nitrite or strong nitric acid, that maintain the passive state on some metals and alloys.8... 

When such data are available, they can be used in alloy selection. Stress corrosion situations cannot always be avoided. Under such circumstances alloys which have a low plateau maximum velocity can be chosen in preference to alloys with a high plateau velocity under circumstances where the same alloys are metallur-gically equivalent or interchangeable. Examples of this have been given in the literature ( ). ... 

The effect of H2S concentration on total corrosion of selected alloys in 1000 hr at 1800°F is illustrated in Fig. 2. A variety of different oxidation-corrosion behaviors were observed. Ferritic alloys, like AISI 446, generally showed increased corrosion rate with decreasing H2S concentration, whereas 300 series austenitics typified by AISI 310 generally exhibited maxima at both 0.1 and 1.0 v/o H2S. IN-800 had high corrosion only above 0.5 v/o H2S. Aluminized AISI 310 and IN-800, IN-671, and several high-chromium alloys did not indicate a strong dependence of H2S concentration in 1000 hr total corrosion. Cobalt-base alloys also generally performed as shown for the aluminized AISI 310 and IN-671 specimen. 

Figure 1. Effect of temperature on 1000-hour total corrosion of selected alloys in CGA environment containing 1 v/o H2S...

Bhattachar3iya, S., Bock, F. C., MacNab, A., and Cox, T. B., "Alloy Selection for Coal Gasification Quench Systems," Paper No. 51, NACE, Corrosion/77,... 

The exercise of alloy selection for agiven application takes all of the above factors into account. While other properties are mentioned from time to time, the emphasis of this book is on oxidation and corrosion behaviour. 

Weldments of nonheat-treatable alloys are resistant to corrosion. In the case of heat-treatable alloys, corrosion is selective in the weld or in the HAZ. Welding can crack because of mercury-zinc amalgam. 

R.H. Kane, Alloy selection for high temperature corrosives, in B.J. Moniz, W.I. Pollock (Eds.), Process Industries Corrosion, NACE, Houston, 1986, pp. 45—65. 

For example, Alloy Selection System for Elevated Temperature (ASSET) is an information system that combines an assessed experimental database and thermochemical computations for a given alloy and high-temperature gaseous environment to predict corrosion as a function of time and... 

Lai, G. Y., "High-Temperature Corrosion Issues in Alloy Selection, Journal of Metals, November 1991, pp. 54-60. 

Corrosion of materials in sour water stripping operations involves complex mixtures of sulfides, cyanides, carbonates, and chlorides. Corrosion control is by alloy selection. 

The RBI approach can be used to evaluate the risk reduction associated with alternative alloys. Coupled with appropriate alloy cost information, the replacement alloy selection can be optimized on a risk reduction versus cost basis. Used in this manner, the RBI program becomes a valuable tool for the corrosion engineer. This type of output from an RBI program can be used when communicating with management about the justification of the added cost of a material upgrade [3]. 

Lai GY. High-temperature corrosion Issues in alloy selection. Journal of Materials 1991 54-60. 

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