This article examines the characteristics and behavior of scale produced by various types of oxidation. The basic models, concepts, processes, and open questions for high-temperature gaseous corrosion are presented. The article describes the development of geometrically induced growth stresses, transformation stresses, and thermal stresses in oxide scales. It discusses the ways in which stresses can be relieved. The article provides information on catastrophic oxidation, internal oxidation, sulfidation, alloy oxidation, selective oxidation, and concurrent oxidation. It illustrates the relationships between scale morphologies on binary alloys and concludes with a discussion on metal dusting and chlorine corrosion.

This article discusses two approaches for determining gaseous corrosion rates, one based on indirect (discontinuous) measurements, the other based on direct (continuous) measurements. It explains how corrosion rate data can be obtained indirectly by measuring scale thickness, scale weight per unit surface area, loss of metal thickness, loss of material weight per unit surface area, or weight change of oxidant bonded in the scale per unit surface area as a function of time. It also describes several continuous methods, including volumetric measurements, the manometric method, and thermogravimetric analysis, and the conditions under which they can be used.

When metal is exposed to an oxidizing gas at elevated temperature, corrosion can occur by direct reaction with the gas, without the need for the presence of a liquid electrolyte. This type of corrosion is referred to as high-temperature gaseous corrosion. This article describes the various forms of high-temperature gaseous corrosion, namely, high-temperature oxidation, sulfidation, carburization, corrosion by hydrogen, and hot corrosion.

This article provides a discussion on the mechanisms of wear and their interactions with gaseous corrosion. The wear mechanisms include abrasive, erosive, fretting, and sliding. The measurement of degradation on combustion walls in coal-fired boilers is discussed. The article concludes with information on the common coating techniques used for wear-corrosion control.

Metals can react chemically with oxygen when exposed to air. Essential to an understanding of the gaseous corrosion of a metal are the crystal structure and the molar volume of the metal on which the oxide builds, both of which may affect growth stresses in the oxide. This article presents crystal structures and thermal properties of pure metals and oxides in a tabular form. The free energy of reaction, which describes the oxidation process of a pure divalent metal, is presented. The article illustrates the Richardson-Jeffes diagram, which is used in the determination of the standard Gibbs energy change of formation of oxides and the corresponding dissociation pressures of the oxides as a function of temperature. It demonstrates the Kellogg diagram which shows stability range in more complicated multioxidant systems. The article explains the determination of partial pressures of gas mixtures and partial pressures of volatile oxidation products.

This article provides information on the thermodynamics and kinetics of high-temperature corrosion. The thermodynamics of high-temperature corrosion reactions reveals what reactions are possible under certain conditions and kinetics explains how fast these possible reactions will proceed. The article describes the diffusion process that plays a key role in oxidation and other gaseous reactions with metals. It discusses the development of stress in oxide layers. The article presents the sample preparation methods for high-temperature testing, and expounds the measurement methods of high-temperature degradation. It reviews a number of potential processes, which are responsible for high-temperature corrosion. The article details a wide range of coatings and coating processes for protecting components in a variety of operating conditions. It also discusses the testing methods used for materials at high temperatures, including furnace tests, burner rig testing, and thermogravimetric analysis, and the test methods conducted at high temperature and high pressure.

This article describes the Schottky defect and the Frenkel defect in oxides. It provides information on the p-type metal-deficit oxides and n-type semiconductor oxides. The article discusses diffusion mechanisms and laws of diffusion proposed by Fick. It explains the oxide texture of amorphous and epitaxy oxide layers and presents equations for various oxidation reaction rates. The article reviews different theories to describe the oxidation mechanism. These include the Cabrera-Mott, Hauffe-IIschner, Grimley-Trapnell, Uhlig, and Wagner theories.

This article provides a summary of the concepts discussed in the articles under the Section “Fundamentals of Corrosion” in ASM Handbook, Volume 13A: Corrosion: Fundamentals, Testing, and Protection. In this section, the thermodynamic aspects of corrosion are descried first followed by a group of articles discussing the fundamentals of aqueous corrosion kinetics. The fundamentals of gaseous corrosion are addressed next. The fundamental electrochemical reactions of corrosion and their uses are finally described.

Corrosion is classified into two categories: corrosion that is not influenced by any other process and corrosion that is influenced by another process such as the presence of stresses or erosion. This article discusses uniform corrosion, localized corrosion, metallurgically influenced corrosion, and microbiologically influenced corrosion, which fit under the classification of corrosion that is not influenced by any outside process. It also explains mechanically assisted degradation and environmentally induced cracking, which fit under the classification of corrosion that is influenced by an outside process.

This article provides an introduction to the fundamentals of corrosion in gases. It tabulates the structures and properties of oxides as well as the physical properties of pure metals.

This article is a pictorial guide to forms of corrosion that draws attention to common pitfalls or situations that have caused premature corrosion, sometimes with expensive consequences. The examples used are not exhaustive; they highlight the necessity to fully examine materials, conditions, and specific circumstances that together can reduce the anticipated service life of a component or plant. The color images in this article are categorized according to the type of corrosion following the general order that is adopted in Volume 13A of ASM Handbook. The first table of the article provides a categorization of the forms of corrosion. It also provides a reference to articles or sections of articles in Volume 13A that detail the particular corrosion form or mechanism. The second table is a guide listing the figures in this article by material and by the corrosion form or mechanism illustrated.

This article reviews general corrosion of uranium and its alloys under atmospheric and aqueous exposure as well as with gaseous environments. It describes the dependence of uranium and uranium alloy corrosion on microstructure, alloying, solution chemistry, and temperature as well as galvanic interactions between uranium, its alloys, and other metals. The article provides information on the atmospheric corrosion of uranium based on oxidation in dry air or oxygen, water vapor, and oxygen-water vapor mixtures depending upon particular storage conditions. The mechanism and morphology of hydride corrosion of uranium are discussed. The article provides information on environmentally assisted cracking, protective coatings, and surface modification of uranium and its alloys. It also summarizes the environmental, safety, and health considerations for their use.

Steel storage tanks are the primary means for storing large volumes of liquids and gaseous products. The stored fluid could be water, but it could also be volatile, corrosive, and flammable fluid requiring special precautions for storage as well. Corrosion is generally worst where the tank is in contact with the soil. This article describes the soil characteristics and addresses cathodic protection (CP) criteria for submerged metallic piping systems. It provides information on the data required for designing a CP system, alone or in conjunction with a protective coating system. These data are collected from predesign site assessments, tank electrical characteristics, and soil-resistivity measurements. The article addresses NACE Standard RP0169, which gives requirements and desired characteristics for coating in conjunction with CP. It also explains the methods of protecting aboveground storage tanks and underground storage tanks.

Understanding the high-temperature corrosion behavior of alloys is an important step toward the selection of appropriate alloys for process equipment. This article briefly describes the high-temperature corrosion modes that are frequently encountered in the chemical process industry. These modes include oxidation, carburization, metal dusting, nitridation, halogen corrosion, and sulfidation.

High-temperature exposure of materials occurs in many applications such as power plants (coal, oil, natural gas, and nuclear), land-based gas turbine and diesel engines, gas turbine engines for aircraft, marine gas turbine engines for shipboard use, waste incineration, high-temperature fuel cells, and missile components. This article discusses high-temperature corrosion in boilers, diesel engines, gas turbines, and waste incinerators. Boilers are affected by stress rupture failures, waterside corrosion failures, fireside corrosion failures, and environmental cracking failures. Contamination of combustion fuel in diesel engines can cause high-temperature corrosion. Gas turbine engines are affected by hot corrosion. Refractory-lined incinerators and alloy-lined incinerators are discussed. The article provides case studies for each component failure.

This article discusses the corrosion of metals and nonmetals by dry chlorine, refrigerated liquid chlorine, dry gaseous chlorine, moist chlorine, selected mixed gases with chlorine, and chlorine-water. It also provides information on the handling of commercial chlorine.

Nitriding is a general term for all processes based on the addition of nitrogen to the surface of steel. When carbon is added along with the nitrogen, the process is called nitrocarburizing. This article provides a detailed discussion on the functional and structural properties of nitrided layers. It describes the structural changes on the surface of carbon steels, alloy steels, and austenitic stainless steels. The article explains the effects of the various nitriding processes, namely, gaseous nitriding, plasma nitriding, gaseous nitrocarburizing, and salt bath nitrocarburizing, on the structure and properties of nitrided layers.

Surface modification is the alteration of the surface composition or structure using energy or particle beams. This article discusses two different surface modification methods. The first, ion implantation, is the introduction of ionized species into the substrate using kilovolt to megavolt ion accelerating potentials. The second method, laser processing, is high-power laser melting with or without mixing of materials precoated on the substrate, followed by rapid melt quenching. The article also describes the advantages and disadvantages of the surface modification approach to promote corrosion resistance.

Low-temperature surface hardening is mostly applied to austenitic stainless steels when a combination of excellent corrosion performance and wear performance is required. This article provides a brief history of low-temperature surface hardening of stainless steel, followed by a discussion on physical metallurgy, including crystallographic identity, thermal stability and decomposition, nitrogen and carbon solubility in expanded austenite, and diffusion kinetics of interstitials. It provides a description of low-temperature nitriding and nitrocarburizing processes for primarily austenitic and, to a lesser extent, other types of stainless steels along with practical examples and industrial applications of these steels.