High-temperature corrosion description

Concepts of local equilibrium and charged particle motion under - electrochemical potential gradients, and the description of high-temperature -> corrosion processes, - ambipolar conductivity, and diffusion-controlled reactions (see also -> chemical potential, -> Wagner equation, -> Wagner factor, and - Wagner enhancement factor). 

The overall simulation of high-temperature corrosion processes under near-service conditions requires both a thermodynamic model to predict phase stabilities for given conditions and a mathematical description of the process kinetics, i.e. solid state diffusion. Such a simulation has been developed by integrating the thermodynamic program library, ChemApp, into a numerical finite-difference diffusion calculation, InCorr, to treat internal oxidation and nitridation of Ni-base alloys [10]. This simulation was intended to serve as a basis for an advanced computer model for internal oxidation and sulfidation of low-alloy boiler steels. 

Section V on Testing in Environments (H. Hack, Section Editor) includes chapters on outdoor and indoor atmospheres, seawater, fresh water, soils, concrete, industrial waters, industrial chemical, petroleum, high-temperature gases, organic liquids, molten salts, liquid metals, corrosion inhibitors, in-vivo, and microbiological effects. Each chapter provides a descriptive overview of the environment and factors and variables affecting corrosion rates and mechanisms. 

Description and corrosion resistance. Alloy 800 is a nickel-iron-chromium alloy with good strength and excellent resistance to oxidation and carburization in high-temperature atmospheres. It also resists corrosion by many aqueous environments. 

Description Ammonia and C02 react at synthesis pressure of 140 bar to urea and carbamate (Fig. 1). The conversion of ammonia as well as C02 in the synthesis section is 80% resulting in an extreme low recycle flow of carbamate. Because of the high-ammonia efficiency, no pure ammonia is recycled in this process. The synthesis temperature of 185°C is low, and, consequently, corrosion in the plant is negligible. 

Description Ammonia and carbon dioxide react at 155 bar to synthesize urea and carbamate. The reactor conversion rate is very high under the N/C ratio of 3.7 with a temperature of 182-185°C. Unconverted materials in synthesis solution are efficiently separated by C02 stripping. The milder operating condition and using two-phase stainless steel prevent corrosion problems. Gas from the stripper is condensed in vertical submerged carbamate condenser. Using an HP Ejector for internal synthesis recycle, major synthesis equipment is located on the ground level. 

Description Ammonia and carbon dioxide react at 150 bar to yield urea and ammonia carbamate. The conversion in the reactor is very high due to favorable NH3/CO2 ratio of 3.5 1 and operating temperature of 185°C to 190°C. These conditions prevent corrosion problems. Carbamate is decomposed in three stages at different pressures in the stripper at the same pressure as the reactor, in the medium-pressure decomposer at 18 bar and in the low-pressure decomposer at 4.5 bar. 

Details of the corrosion of these fwo phases, as well as tor YBa Cu O, are described. Finally, descriptions of electrochemical polymerization and deposition of conductive molecular films onto the high T phases, and fabrication of conductive polymer/high T supercSnductor microstructures, are provided. All of these experiments are conducted at room temperature. 

Description and corrosion resistance. This alloy s high critical pitting crevice temperatures provide more resistance to pitting and crevice corrosion than lesser-alloyed materials. The very high yield strength of this alloy combined with good ductihty allows lower wall thickness in process equipment. 

Description and corrosion resistance. Alloy 600 is a nickel-chromium alloy designed for use from cryogenic to elevated temperatures in the range of 1093°C. The high nickel content of the alloy enables it to retain considerable resistance under reducing conditions and makes it resistant to corrosion by a nmnber of organic and inorganic compounds. 

Treatment of chromia under flow conditions and at moderate temperatures with a variety of C, CFCs or hydrochlorofluorocarbons (HCFCs) or Cj HFCs is an alternative way of producing a fluorinated chromia surface that is catalytically active [24]. It has the advantage that corrosive reagents such as anhydrous HE are avoided. XPS and X-ray excited Auger electron spectroscopy (XAES) demonstrate clearly the points in the processes where activation occurs formation of amorphous highly fluorinated regions at the surface is indicated. Description of local structure is less easily made, although a... 

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