Sulfidation high-temperature corrosion

High-temperature corrosion frequently shows general corrosion, as in oxidation, sulfidation, carburization, hot corrosion and hydrogen effects, etc. It should be noted that subsurface corrosion or internal corrosion at high-temperature corrosion is a highly localized corrosion phenomenon. 

Reprinted from Computer Correlations to Estimate High Temperature Hydrogen Sulfide Corrosion in Refinery Streams," Materials Protection, January 1971.)... 

High-temperature Corrosion of Metals by Cases 643 product oxide, sulfide, or halide ... 

Vanadium in a fuel forms various metal compounds with low melting points, and causes molten-salt corrosion of steel called vanadium attack. Another example of high temperature corrosion is sulfidation. Carbon monoxide, carbon dioxide, and hydrocarbons form metal carbides at high temperatures and this is called carburization. Nitriding involves chemical reaction of nitrogen with metal. 

The melting temperature of sulfides is generally lower than that of oxides. For example, for NiS it is 797 °C, compared to 1990 °C for NiO. In addition, the sulfides of Ni, Co, Fe and Cr can form eutectics with the base metal lowering even more their melting temperature for example, in the system Ni-S the eutectic melts at 645 °C already. Nickel sulfides therefore melt easily under typical high-temperature corrosion conditions. On the other hand, chromium sulfides melt less easily the Cr-S eutectic having a melting temperature of 1350 °C. 

Lai, G. Y., Sulfidation, High Temperature Corrosion of Engineering Alloys, ASM Intemationtil, Metals Park, OH, 1990, p. 123. 

NACE Technical Committee Report, 56-7, "Collection and Correlation of High Temperature Hydrogen Sulfide Corrosion Data, Corrosion, Vol. 12, 1956, p. 213. 

The high-temperature corrosion of metals and alloys in sulfidizing-oxidizing environments has been reviewed by Stroosnij-der and Quadakkers (1986), Gesmundo et al. (1989), and Grabke et al. (1989). On the basis of equilibrium thermodynamics, the transition from oxidation to sulfidation of alloy constituent B should occur when ... 

Although all high-temperature corrosion is considered oxidation, there are other terms that are also encountered, such as oxidation-reduction, sulfidation, fuel ash corrosion, carburization, and nitridation, to name a few. 

Haynes alloy 556 exhibits useful resistance to a wide variety of high-temperature corrosive atmospheres as well as molten salts. The presence of approximately 18% cobalt results in more resistance to sulfidation than... 

Sulfidation is a common high-temperature corrosion-failure mechanism. As the name implies, it is related to the presence of sulfur compounds. When examining this form of damage microscopically, a "front" of sulfidation is often seen to penetrate into the affected alloy. Localized pitting-t5 e attack is also possible. A distinction can be made between sulfidation in gaseous environments and corrosion in the presence of salt deposits on corroding surfaces. Only the former is considered in this section, the latter being discussed in... 

Environmental corrosion and degradation of metals and alloys impose enormous losses in modem industrial societies. In Chapter 140 Hinton considers a wide variety of methods using rare-earth solutions and salts to modify advantageously the costly deterioration of metals and alloys. This topic is expanded by Ryan in Chapter 141, giving particular attention to protection against high-temperature oxidation, sulfidization and hot-salt corrosion. 

High-temperature refinery corrosion is caused by various sulfur compounds originating from crude oil. Sulfidic corrosion rate correlations are available and therefore equipment life can be predicted with some degree of reliability. Different types of high-temperature corrosion are named as follows ... 

Figure 1.4 Effect of temperature and hydrogen sulfide content on high-temperature corrosion...

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. 

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