Corrosion testing and monitoring are powerful tools in the fight to control corrosion. This chapter provides a general overview of three major categories of corrosion tests, namely laboratory tests, pilot-plant tests, and field tests. It begins with brief sections describing the purposes of corrosion tests, the logical steps in a test program, and the preparation and cleaning of test specimens. The focus then moves on to discuss the types and applications of these test categories and the associated evaluation procedures. Excluding electrochemical tests which are addressed separately in this chapter, the other laboratory tests covered under this category are simulated atmosphere tests, salt-spray tests, and immersion tests. Only corrosion testing in the atmosphere is discussed in the section on field tests. Corrosion monitoring techniques are finally considered, covering the characteristics of corrosion monitoring techniques, the factors to be considered in selecting a corrosion-monitoring method, and the strategies in corrosion monitoring.

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.

Anodic protection is used on a smaller scale than other corrosion control techniques due to the fundamental electrochemistry involved. This chapter provides a brief history of the technique, discusses anodic protection use, and compares anodic and cathodic protection. The background and theory of anodic protection are summarized. In addition to briefly describing the various items used for each component of an anodic protection system, the chapter presents design concerns as well as applications of the system. Factors concerning the economic justification of anodic protection are also described.

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 article describes in detail the process of corrosion control by cathodic and anodic protection. The discussion covers the basic concept of cathodic and anodic protection systems, their types and equipment used, and the advantages, limitations, and applications of these protection systems. The types of cathodic protection systems include sacrificial cathodic protection and impressed-current cathodic protection systems. Some of the technical problems associated with cathodic protection include the effects of stray currents on the corrosion of adjacent metal structures, the effects of the chemical reactions occurring at the surface of the protected structure, and the effects of cathodic protection on coatings.

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.

Corrosion is a key subject for more or less all classes of alloys that fall within the broad definition of stainless steels because these alloys were developed with the intention of preventing corrosion. This chapter provides an introduction to the fundamentals of electrochemical theory as it pertains to corrosion resistance of stainless steels. The discussion provides an overview of electrochemical reactions, Faraday's law, the Nernst equation, galvanic versus electrochemical cells, corrosion tendency, and Pourbaix diagrams.

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.

Corrosion can be defined as a chemical or electrochemical reaction between a material and its environment that causes the material and its properties to degrade. In most cases, it refers to the electrochemical oxidation of metals accompanied by the production of oxides or salts of the base material. This chapter discusses the process of corrosion and how to prevent or mitigate its effects. It describes several forms of corrosion, including uniform, intergranular, pitting, crevice, and stray-current corrosion, and the effects of stress-corrosion cracking, corrosion fatigue, and selective leaching. It discusses the use of corrosion inhibitors, cathodic and anodic protection, pH control, and Pourbaix diagrams.

This chapter provides a detailed account of cathodic protection. It begins by discussing the fundamentals of cathodic protection followed by a description of the various types of cathodic protection. It then describes the origins, types, and alleged failures of cathodic protection criteria. This is followed by a section providing information on anode materials that are used for cathodic protection applications. General guidelines for designing the cathodic protection systems are also listed. Finally, the chapter presents various examples on cathodic protection of steel structures. The examples are selected to familiarize the design engineer with the steps to follow in selecting a specific corrosion-control method.

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 describes the factors that affect the corrosion performance of aluminum assemblies joined by methods such as welding, brazing, soldering, and adhesive bonding. The factors covered include galvanic effects, crevices, and assembly stresses in products susceptible to stress-corrosion cracking.

This chapter discusses some of the metallurgical factors that affect corrosion of weldments and describes a few considerations for selected nonferrous alloy systems: aluminum, titanium, tantalum, and nickel.

This chapter discusses corrosion prevention methods used with aluminum and its alloys. The methods range from relatively straightforward measures, such as proper handling and storage, to advanced early warning corrosion monitoring systems for military aircraft. The chapter summarizes the basic factors that influence design for corrosion resistance and discusses the use of conversion coatings, organic coatings, porcelain enameling, and electroplating. It also discusses corrosion monitoring methods used in chemical processing and refining industries.

This chapter discusses the corrosion behavior of titanium, the types of corrosion that can occur, and the effect of alloying on corrosion resistance. It explains that, due to its tenacious oxide film, titanium has excellent corrosion resistance in oxidizing environments and that the resistance can be extended into the “reducing-acid” region by adding a small amount of palladium. It describes how different grades of titanium respond to different forms of attack, including uniform, crevice, and galvanic corrosion. It also identifies applications where corrosion is often a concern.

This chapter concentrates on the better-known and widely studied phenomenon of pitting corrosion of passive metals. The discussion focuses on different parameters that influence pitting corrosion, namely environment, metal composition, potential, temperature, surface condition, and inhibitors. It also provides information on various stages of pitting: passive film breakdown, metastable pitting, pit growth, and pit stifling or death.

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.