Steels with chromium contents above 12% show high resistance to oxidation and corrosion and are generally designated as stainless steels. This chapter discusses the compositions, microstructures, heat treatments, and properties of martensitic, ferritic, austenitic, ferritic-austenitic (duplex), and precipitation hardening stainless steels. It also describes solidification sequences and explains how chromium carbides may segregate to grain boundaries at certain temperatures, making grain boundary regions susceptible to intercrystalline or intergranular corrosion.

Stainless steels and nickel-base alloys are recognized for their resistance to general corrosion and other categories of corrosion. This chapter examines the effects of specific alloying elements, metallurgical structure, and mechanical conditioning on the corrosion resistance of these alloys. Some categories of corrosion covered are pitting, crevice, intergranular, stress-corrosion cracking, general, and high-temperature corrosion.

This chapter outlines the step-by-step processes by which materials are selected in order to prevent or control corrosion and includes information on materials that are resistant to the various forms of corrosion. The various forms of corrosion covered are general (uniform) corrosion, localized corrosion, galvanic corrosion, intergranular corrosion, stress-corrosion cracking, hydrogen damage, and erosion-corrosion. In addition, the economic importance of cost-effective materials selection is also considered.

This chapter discusses common forms of corrosion, including uniform corrosion, galvanic corrosion, pitting, crevice corrosion, dealloying corrosion, intergranular corrosion, and exfoliation. It describes the factors that contribute to stress-corrosion cracking, hydrogen embrittlement, and corrosion fatigue and compares and contrasts their effects on mechanical properties, performance, and operating life. It also includes information on high-temperature oxidation and corrosion prevention techniques.

This chapter focuses on the applications of stainless steels in chemical and process industry, covering what data are necessary and how they can be found. It begins with an overview of single- and dual-environment systems and the corrosion issues they face. This is followed by a discussion on the causes of the various forms of corrosion associated with liquids, namely pitting corrosion, crevice corrosion, intergranular corrosion, stress corrosion cracking, and erosion corrosion. The chapter also contains tables listing corrosion rates of sulfuric acid and fuming sulfuric acid. It ends with a section providing information on specific environments against which stainless steels are resistant to select for use in the chemical process industries.

This chapter first covers some basic principles of electrochemical corrosion and then some of the various types of corrosion. Some of the more common types of corrosion discussed include uniform corrosion, galvanic corrosion, pitting, crevice corrosion, erosion-corrosion, cavitation, fretting corrosion, intergranular corrosion, exfoliation, dealloying corrosion, stress-corrosion cracking, and corrosion fatigue. The chapter discusses the processes involved in corrosion control by retarding either the anodic or cathodic reactions. The rate of corrosion is reduced by conditioning of the metal, by conditioning the environment, and by electrochemical control. Finally, the chapter deals with high-temperature oxidation that usually occurs in the absence of moisture.

Austenitic stainless steels exhibit a single-phase, face-centered cubic structure that is maintained over a wide range of temperatures. This chapter provides a basic understanding of grade designations, properties, and welding considerations of austenitic stainless steels. It also discusses general types of corrosive attack and their effects on service integrity as well as detection and control measures. The five corrosive attack mechanisms covered are intergranular corrosion, preferential attack associated with weld metal precipitates, pitting and crevice corrosion, stress-corrosion cracking, and microbiologically influenced corrosion.

Ferritic stainless steels are essentially iron-chromium alloys with body-centered cubic crystal structures. Chromium content is usually in the range of 11 to 30%. The primary advantage of the ferritic stainless steels, and in particular the high-chromium, high-molybdenum grades, is their excellent stress-corrosion cracking resistance and good resistance to pitting and crevice corrosion in chloride environments. This chapter provides information on the classifications, properties, and general welding considerations of ferritic stainless steels. The emphasis is placed on intergranular corrosion, which is the most common cause of failure in ferritic stainless steel weldments. Two case histories involving intergranular corrosion failures of ferritic stainless steel weldments are included. A brief discussion on hydrogen embrittlement is also provided.

This chapter addresses in-service monitoring and corrosion testing of weldments. Three categories of corrosion monitoring are discussed: direct testing of coupons, electrochemical techniques, and nondestructive testing techniques. The majority of the test methods for evaluating corrosion of weldments are used to assess intergranular corrosion of stainless steels and high-nickel alloys. Other applicable tests evaluate pitting and crevice corrosion, stress-corrosion cracking, and microbiologically influenced corrosion. Each of these test methods is reviewed in this chapter.

This chapter lays the groundwork for understanding electrode kinetics associated with corrosion. It presents a simple but useful theory relating kinetics to the polarization behavior of half-cell reactions. The theory is based on the observation that electrode potentials vary as a function of current density or charge transfer in a given area. The chapter explains how to measure and plot electrode potentials and currents and how to interpret the resulting polarization curves. It also discusses the effects of concentration gradients, explaining how they cause diffusion and, in some cases, produce changes in electrode potential.

This chapter develops a corrosion model that accounts for solution potentials and the effects of coupling between cathodic and anodic reactions. It begins by examining potential differences at various points (in the solution) along a path from the anode to the cathode area. It then presents a simple model of a galvanically coupled electrode, in which the metal is represented as an array of anode and cathode reaction surfaces. The chapter goes on to develop the related theory of mixed electrodes, showing how it can be used to predict corrosion rates based on measured potentials and current densities, polarization characteristics, and physical variables such as anode-to-cathode area ratios and fluid velocity. It also discusses the effect of corrosion inhibitors, galvanic coupling, and external currents, making extensive use of polarization curves.

This chapter discusses the principles and procedures of electrochemical measurements used to investigate corrosion behaviors. It begins by presenting a diagram of a basic potentiostatic circuit, which consists of a working electrode and an auxiliary or counter electrode suspended in an electrolytic solution. It describes how corrosion potentials and current densities are measured and explains how to deal with various sources of error. It also explains how electrochemical impedance measurements are used and describes the underlying theory and procedures in some detail.

This chapter familiarizes readers with the basic concepts of corrosion, discussing chemical reactions, ion transfer mechanisms, electrochemical processes and variables, and the formation of solid corrosion products. It presents a simple but effective teaching tool, the elementary electrochemical corrosion circuit, using it to explain how electric potential differences drive the corrosion process and how corrosion rates vary in proportion to current density. The chapter concludes with a discussion on the importance of corrosion products, such as oxides and hydroxides, and how their formation can be a major factor in controlling corrosion.

This chapter provides a thorough introduction to the electrochemical thermodynamics that govern electrode reactions associated with corrosion. It begins with a review of the thermodynamic criteria for the stability of chemical reactions based on Gibbs free energy and explains how energies of formation are determined using the oxidation of iron as an example. It then considers how iron reacts with hydrochloric acid, explaining how it can be expressed as two half reactions modeled as electrodes in an electrochemical cell. It goes on to describe the chemical reactions occurring at each electrode, accounting for different variables, mechanisms, and electrochemical effects. The chapter concludes with an in-depth review of Pourbaix diagrams, explaining what they reveal about the stability of metal-water systems and the formation of corrosion products.

This chapter discusses the complex polarization characteristics of active-passive metals and addresses related problems in interpreting their corrosion behavior. It begins by presenting several experimentally derived polarization curves for iron, comparing and contrasting them with the iron-water Pourbaix diagram. It then explains how anodic polarization is extremely sensitive to the environment and, as a result, a reasonably complete curve for a given metal-environment system usually can only be inferred. It goes on to describe how such curves are constructed, demonstrating the procedures for a wide range of alloys and environments. The examples also show how factors such as alloy concentration, crystal lattice orientation, temperature, and dissolved oxygen affect corrosion behavior.

This chapter is a detailed study of the localized corrosion behavior of steel, copper, and aluminum alloys. It applies the basic principles of electrochemistry, as well as materials science and solid and fluid mechanics, to explain the causes and effects of pitting, crevice corrosion, stress corrosion cracking, and corrosion fatigue. It describes the underlying mechanisms associated with each process and how they relate to the microstructure of the metal or alloy, the physical condition of the surface, and other factors such as the coupling of the metal to a dissimilar metal or surface film.

This appendix is a comprehensive collection of selected sources related to corrosion properties of materials and corrosion testing.

Corrosion problems can be divided into eight categories based on the appearance of the corrosion damage or the mechanism of attack: uniform or general corrosion; pitting corrosion; crevice corrosion, including corrosion under tubercles or deposits, filiform corrosion, and poultice corrosion; galvanic corrosion; erosion-corrosion, including cavitation erosion and fretting corrosion; intergranular corrosion, including sensitization and exfoliation; dealloying; environmentally assisted cracking, including stress-corrosion cracking, corrosion fatigue, and hydrogen damage (including hydrogen embrittlement, hydrogen-induced blistering, high-temperature hydrogen attack, and hydride formation). All these forms are addressed in this chapter in the context of aqueous corrosion. For each form, a general description is provided along with information on the causes and the list of metals that can be affected, with particular emphasis on the recognition and prevention measures.

Aluminum is the second most widely used metal in the world. It is readily available, offers a wide range of properties, and can be shaped, coated, and joined using a variety of methods. This chapter discusses some of the key attributes of wrought and cast aluminum alloys and the classifications, designations, and grades of available product forms. It also explains how aluminum alloys are used in aerospace, automotive, rail, and marine applications as well as in building and construction, electrical products, manufacturing equipment, packaging, and consumer durables such as appliances and furniture.