This chapter discusses the effects of corrosion on boiler tube surfaces exposed to water and steam. It describes the process of corrosion, the formation of scale, and the oxides of iron from which it forms. It addresses the primary types of corrosion found in boiler environments, including general corrosion, under-deposit corrosion, microbially induced corrosion, flow-accelerated corrosion, stress-assisted corrosion, erosion-corrosion, cavitation, oxygen pitting, stress-corrosion cracking, and caustic embrittlement. The discussion is supported by several illustrations and relevant case studies.

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.

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 major types of corrosion, their interactions, their complicating effects on fracture and wear, and some possible prevention methods. The types of corrosion considered in the chapter are galvanic corrosion, uniform corrosion, pitting corrosion, crevice corrosion, microbiologically influenced corrosion, stress-corrosion cracking, and corrosion fatigue.

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.

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 covers the corrosion behavior of beryllium in aqueous environments. It describes the chemical reactions that drive the corrosion process, the conditions required for equilibrium, and the factors that affect corrosion resistance. It discusses the stability of the native oxides that form on the surface of beryllium and their ability to withstand acids, bases, and corrosive agents found in rain and seawater. It explains how carbides, inclusions, ions, and impurities contribute to corrosion damage, particularly pitting, and how corrosion reduces the ductility and fracture strength of certain beryllium alloys.

This chapter explores the behavior of stainless steel in media that promote corrosion. The forms of corrosion covered are uniform corrosion, atmospheric corrosion, localized corrosion, pitting corrosion, crevice corrosion, and grain boundary corrosion. The chapter discusses the influence of material and environmental variables on stress-corrosion cracking (SCC) and the mechanisms proposed for SCC in stainless steel, comparing the mechanism of SCC with hydrogen embrittlement. In addition, it provides information on biocorrosion and microbiologically induced corrosion in ambient aqueous environments.

This chapter provides information on the structure, design aspects, mechanical properties, forming, machining, and corrosion resistance characteristics of duplex stainless steels. The different types of corrosion covered are general corrosion, pitting corrosion, crevice corrosion, and stress corrosion cracking.

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 provides information on various contributors to failure of carburized and carbonitrided components, with the primary focus on carburized components. The most common contributors covered include component design, selection of proper hardenability, increased residual stress, dimensional stability, and generation of quenching and grinding cracks. They also include insufficient case hardness and improper core hardness, influence of surface carbon content and grain size, internal oxidation, structure of carbides, and inclusion of noncarbide. Details on micropitting, macropitting, case crushing, pitting corrosion, and partial melting are also provided.

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.

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.

A first-stage compressor blade failed prematurely in an aircraft engine, fracturing at the midpoint of the root transition region. An examination of the fracture surface revealed beach marks, striations, and pitting, indicating that the blade failed by fatigue due to a crack initiated by corrosion pits in the root transition region. The chapter recommends further investigations to determine the cause of pitting, which appears to be confined to the dovetail region.

This chapter discusses the failure of a first-stage compressor blade in an aircraft engine and explains how investigators determined that it was caused by fatigue, with a crack originating from corrosion pits that developed in the root transition region on the convex side of the airfoil.

The tail rotor blade of a helicopter developed a visible crack during service. The cracked region was removed from the blade and the fracture surface was examined in a SEM, revealing shallow pitting on the inside surface of the skin and a corresponding reduction in thickness. Based on these findings, investigators concluded that the failure was due to a fatigue crack initiated from a corrosion pit, which may have been caused by chemicals released by the burning of bonding resin.

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.