Skip to main content
main-content
Top

About this book

This textbook discusses the latest advances in the corrosion of metals and related protection methods, and explores all corrosion-related aspects used in natural and industrial environments, including monitoring and testing. Throughout the textbook, the science and engineering of corrosion are merged to help readers perform correct corrosion assessments in both the design phase and plant management phase, and to define the optimal protection technique. In addition, the book addresses basic aspects of corrosion science, including the electrochemical mechanism, thermodynamic and kinetic aspects, the use of Pourbaix and Evans diagrams, and various forms of corrosion (from uniform to localised to stress corrosion phenomena); as well as the protection systems adopted to combat corrosion, including inhibitors, coatings and cathodic protection. Such basic knowledge is fundamental to understanding the “corrosion engineering” approach applied to the durability of metals immersed in water, buried in soil, exposed to the atmosphere, used in reinforced concrete, in the human body and in petrochemical plants, or at risk of high-temperature corrosion. A final chapter is dedicated to the use of statistics in corrosion. All chapters include exercises and practical examples to help students understand, predict, evaluate and mitigate corrosion problems. As such, the book offers the ideal learning resource for all students of corrosion courses in chemical, mechanical, energy and materials engineering at the graduate and advanced undergraduate level, as well as a valuable reference guide for engineers whose work involves real-world applications.

Table of Contents

Frontmatter

Chapter 1. General Principles of Corrosion

Abstract
This introductory chapter presents the general aspects of corrosion: its origins, the main forms it can take, the general mechanism and corrosion rate involved, and the impact it has on society, with particular reference to the economic aspects. All technical information here briefly mentioned will be addressed in more details in specific chapters.
Pietro Pedeferri (Deceased)

Chapter 2. Electrochemical Mechanism

Abstract
Wet corrosion is based on an electrochemical mechanism in which two reactions sum up to give the overall corrosion process; a cathodic reaction that consumes electrons and an anodic one, where electrons are released by the metal oxidation. In this chapter, the electrochemical mechanism is examined in details, and the most important anodic and cathodic processes are described. From these basic principles stoichiometric considerations will be drawn, leading to the correlation between corrosion rate and current density by the use of Faraday law.
Pietro Pedeferri (Deceased)

Chapter 3. Thermodynamics of Aqueous Corrosion

Abstract
This chapter addresses the thermodynamic aspects of corrosion, starting from the concept of free energy: indeed, corrosion can take place only if the free energy variation associated with the reaction is negative, i.e., the reaction is thermodynamically favoured. This translates in terms of variation of potential, outlined as driving voltage, or electromotive force, for the reaction. Standard potentials and equilibrium potentials of anodic and cathodic reactions are defined, together with conditions for corrosion and for immunity. Reference electrodes are presented, which allow to measure the potential as difference between a given electrode and a well defined reference electrode that has the property of maintaining its potential constant. Finally, electrochemical cells, as Daniell or concentration cells, are introduced.
Pietro Pedeferri (Deceased)

Chapter 4. Pourbaix Diagrams

Abstract
In 1945, Marcel Pourbaix (1904–1998) proposed in the Atlas of Electrochemical Equilibria in Aqueous Solutions the potential-pH diagram of elements in the presence of water, which is now called “Pourbaix diagram”. It uses thermodynamic considerations to define potentials corresponding to the equilibrium states of all possible reactions between a given element, its ions, and its solid and gaseous compounds in aqueous solutions as a function of pH. This Chapter illustrates the basis of Pourbaix diagrams, how they are obtained, and shows examples for the most important metals. Three areas can be identified in the diagrams: immunity, corrosion and passivation, representing the fields of thermodynamic stability of the metal, of its ions and of its oxides and hydroxides, respectively.
Pietro Pedeferri (Deceased)

Chapter 5. Kinetics of Aqueous Corrosion

Abstract
This chapter presents the forms of energy dissipation involved in a corrosion process when a positive driving voltage is available for corrosion to take place, as defined by thermodynamics, and how they concur to determine the overall corrosion rate. Dissipations are described in terms of overvoltage of the different processes involved, which are classified as activation overvoltage (metal corrosion, hydrogen evolution), represented by Tafel law, concentration overvoltage (oxygen diffusion) and ohmic drop (electrolyte resistivity). The trend of the overvoltage for an active-passive metal is also described in the different potential ranges, corresponding to immunity, activity, passivity and transpassivity (or localised corrosion).
Pietro Pedeferri (Deceased)

Chapter 6. Evans Diagrams

Abstract
This chapter deals with the potential-current density diagrams, also called Evans diagrams, which relate the variation of potential of a reaction—either anodic or cathodic—with the current density exchanged in the process, starting from its equilibrium potential in the corresponding environmental conditions. These diagrams allow to identify the corrosion working conditions, Ecorr and icorr, where the anodic and cathodic processes proceed with the same rate. The cases of active and active–passive metals are described. Ohmic drop can also be represented on the diagram, modifying corrosion rate. Both corrosion conditions and the imposition of a polarization are discussed with reference to the modification of the electrode working condition that they cause. Finally, experimental polarisation curves are introduced.
Pietro Pedeferri (Deceased)

Chapter 7. Corrosion Factors

Abstract
Corrosion processes involve metal and environment properties through a variety of factors. From the metal side, chemical composition and microstructure play a major role. Chemical composition is also fundamental to define the electrolyte aggressiveness, together with its pH, temperature and the possible presence of bacteria. Other relevant operating conditions are pressure, fluid velocity, presence of mechanical stresses and exposure time. Even though is not easy to depict a general trend on how these factors influence corrosion, a rational approach is proposed for the interpretation, based on thermodynamics (equilibrium potential) and kinetics (Evans diagrams).
Pietro Pedeferri (Deceased)

Chapter 8. Uniform Corrosion in Acidic and Aerated Solutions

Abstract
In this Chapter, the causes and consequences of uniform (or generalized) corrosion are described. This is the simplest form of corrosion, which affects the whole metal surface, and is characterized by the spatial coincidence of anodic and cathodic areas. Corrosion rates range in a very large interval, depending on the environmental conditions, and the phenomenon is easily observed and easily predictable, especially if compared with localized corrosion forms. Here the main conditions leading to uniform corrosion are detailed, from acidic environments to aerated neutral solutions, with reference to the different classes of active and active–passive metals. Moreover, examples of algorithms used to express corrosion rate are provided.
Pietro Pedeferri (Deceased)

Chapter 9. Macrocell Corrosion Mechanism

Abstract
When a macrocell is formed in a corrosion process, an electrical field is established in the environment because a net current flows from the anode to the cathode, which are physically separated. This situation occurs in galvanic corrosion, differential aeration, localized attacks such as pitting and crevice, and cathodic protection. Potential and current distributions are extremely important because they determine the corrosion rate. Analytical solutions of electric fields exist only for very simple geometry and simplified conditions. In the last two decades, the use of numerical calculations based on Finite Element Methods (FEM) has overcome these difficulties. This Chapter gives an overview of macrocell electrical field and current distribution, giving analytical solutions for both quantities in simple geometries, such as inside and outside a pipe. In some of these geometries the throwing power is also evaluated.
Pietro Pedeferri (Deceased)

Chapter 10. Galvanic Corrosion

Abstract
Galvanic corrosion occurs when two or more metals with different practical nobility are electrically connected and immersed in the same environment: the less noble metal experiences an increase in corrosion rate due to the presence of the more noble one. The effects of this coupling on the less noble and the more noble metal are discussed in this chapter and represented by Evans diagram. The main factors influencing the extent of corrosion rate increase are analysed: availability of a driving force for galvanic corrosion, its possible dissipation in cathodic overvoltage and ohmic drop in the electrolyte, ratio between cathodic and anodic areas. Finally, prevention of this localized corrosion phenomenon is briefly described.
Pietro Pedeferri (Deceased)

Chapter 11. Pitting Corrosion

Abstract
This chapter describes a localized corrosion attack called pitting, which is typical of active-passive metals in oxidizing chloride-containing environments: the passive film breaks locally, then corrosion proceeds at the damaged spot, few millimetres wide or even less, creating a macrocell with the surrounding intact passive metal. The influence of metal composition and environmental parameters on corrosion, pitting and repassivation potential for stainless steel in chloride containing environments is shown. Empirical parameters such as Pitting Resistance Equivalent Number (PREN) are discussed and correlated to the likelihood of pitting occurrence. The use of Pedeferri’s diagram, a potential vs chloride content diagram, is also introduced, as a tool to assess corrosion conditions of an active passive metal in chloride-containing environments.
Pietro Pedeferri (Deceased)

Chapter 12. Crevice Corrosion

Abstract
Crevice corrosion is a form of localized corrosion related to the presence of sub-millimetric interstices (gaps, screens, deposits) on the surface of a metal. The mechanism involves the consumption of oxygen in the gap and the impossibility to restore it, with consequent setup of a differential aeration macrocell. This chapter presents the main aspects of metal and environment composition affecting the onset of crevice corrosion and—like in the previous chapter—proposes empirical parameters, as Critical Crevice Gap Size (CCGS), which help predict it.
Pietro Pedeferri (Deceased)

Chapter 13. Stress Corrosion Cracking and Corrosion-Fatigue

Abstract
When a susceptible metal is in contact with a specific environment, in presence of a tensile stress exceeding a threshold, the corrosion-enhanced formation of cracks and catastrophic failure is called stress corrosion cracking (SCC). Although infrequent, consequences are so dangerous that it deserves to be described in details: in this chapter, after the introduction of the SCC mechanism, mechanical, metallurgical and environmental factors at its basis are explained, and specific preventative measurements are suggested. Another form of degradation that links mechanical stress and corrosion, i.e., corrosion-fatigue, is also described.
Pietro Pedeferri (Deceased)

Chapter 14. Hydrogen-Induced Damage

Abstract
Hydrogen induced damage (HID) can occur at high temperature (HT-HID) and at low temperature, (LT-HID). Hydrogen attack, affects steels operating at temperatures typically above 400 °C in high pressure hydrogen atmosphere. The interaction of atomic hydrogen and metals at low temperature occurs in different way. Atomic hydrogen is produced during electroplating processes (as chrome plating, galvanizing and phosphating), chemical and electrochemical pickling treatments, in welding if the humidity of consumables is too high, or by the cathodic process in corrosive fluids: in this last case, so called cathodic poisons, as H2S, inhibit molecular hydrogen formation and promote atomic hydrogen diffusion into the metal. Once entered the metal, atomic hydrogen interacts with the metal structure and may produce a “damage” of various forms, such as delayed fracture, HIC (hydrogen induced cracking) and blistering, hydrogen embrittlement (HE). All of these forms of damage are discussed in this chapter.
Pietro Pedeferri (Deceased)

Chapter 15. Intergranular and Selective Corrosion

Abstract
Metals consist of micrometric size crystalline grains. The border between these grains, called grain boundary, is a peculiar and delicate region, due to a distorted crystallographic structure and possible segregation of impurities and second phases. These characteristics of non-equilibrium make grain boundaries particularly reactive, and weaker in terms of corrosion resistance, so that in some cases a localized corrosion, called intergranular corrosion, can occur. This corrosion-type attack is very severe because it leads to grain detachment, then to a reduced mechanical resistance, despite the negligible metal consumption; in some environments and in the presence of tensile stresses it triggers stress corrosion cracking. In this chapter the most common intergranular corrosion forms are described, including stainless steel sensitization, knife-line attack, exfoliation of aluminium, and selective corrosion of brass and cast iron.
Pietro Pedeferri (Deceased)

Chapter 16. Erosion-Corrosion and Fretting

Abstract
This chapter presents the forms of corrosion related to the contact of a metallic surface with something moving on it, be it a fluid or another material. In the former case, erosion-corrosion phenomena may onset due to the rapid flow of a fluid on a metal, which combines corrosion with physical-mechanical interactions as turbulence, cavitation or impingement of particles on its surface. On the other hand, if a solid body slides on a metal surface, typically in the form of cyclic micrometric slips such as those created by vibration, fretting corrosion establishes, causing a range of damages from simple loss of brightness to the formation of craters that then trigger fatigue cracks.
Pietro Pedeferri (Deceased)

Chapter 17. Corrosion Prevention by Coatings

Abstract
This chapter deals with the method of corrosion prevention based on the use of a physical barrier to separate the metal surface from the environment. This barrier consists of a coat that can be classified, as often generally agreed, into four types, namely: metallic coatings, conversion coatings, inorganic coatings and paints. In this Chapter, only corrosion protection related coatings are considered, although other characteristics, such as mechanical strength, hardness, wear resistance, appearance, and electrical, optical or thermal properties are also of remarkable importance.
Pietro Pedeferri (Deceased)

Chapter 18. Environmental Control

Abstract
An effective and widely used corrosion prevention method is obtained through a modification, often called conditioning, of the aggressive environment. The rationale of the approach is to influence cathodic or anodic processes or both, in order to decrease the corrosion rate below an acceptable limit to meet the design requirement about design life and safety. The main actions, illustrated in the following, are based on the modification of pH, the reduction of oxygen content to slow down the cathodic process, the use of biocides to control microbiological activity, or on the injection of specific chemicals, as scaling agents and corrosion inhibitors, to slow down both anodic and cathodic processes. In particular, for corrosion inhibitors, the mechanism (anodic, cathodic, mixed) is described and the effectiveness is discussed.
Pietro Pedeferri (Deceased)

Chapter 19. Cathodic and Anodic Protection

Abstract
As Volta already observed in early 1800s, a current that is exchanged between a metal surface and the electrolyte to which it is exposed modifies the behaviour of the metal, increasing the corrosion rate or reducing it. Some years later, Davy put in practice such concept demonstrating the possible implications, which, after about a dormant century, started to have effective industrial use: with Davy, cathodic protection was born. A century and a half from Volta’s observations, Edeleanu showed that Hickling potentiostat could control corrosion by making an anodic polarization and Riggs made the first commercial application of anodic protection: hence, anodic protection was also born. Both techniques are set up by establishing a cathodic or anodic current
that is exchanged with the electrolyte, which means supplying or taking electrons. The following chapter deals with these techniques from a theoretical and practical point of view: mechanism, protection criteria, protection potential and current density, applications, monitoring.
Pietro Pedeferri (Deceased)

Chapter 20. Corrosion in Waters

Abstract
All natural and industrial waters are corrosive toward common construction metals if a cathodic process can occur. Oxygen reduction is the most typical cathodic process, for about 95% of dealings, then followed by slightly acidic conditions, the presence of oxidizing species as chlorine and more rarely by bacteria. An important factor that reduces water corrosiveness is the tendency to form protective scales. The main damages due to corrosion are alteration of water quality, especially for drinking water requirements, reduction of components service life, due to wall perforation or other localized corrosion forms, and obstruction inside small pipes due to the high volume of corrosion products. The performance of most used metals are reported with reference to their use in freshwater, brackish and seawater.
Pietro Pedeferri (Deceased)

Chapter 21. Corrosion in Soil

Abstract
Soil can be defined as a complex agglomeration composed of an aqueous solution with solid particles dispersed in, originated from the fragmentation of rock. Its pores entrap either water or air as competitors: these situations determine different corrosion mechanisms, related to the presence (or absence) of oxygen. In this Chapter, the corrosion forms in soil will be described, divided in three main groups: oxygen-related corrosion (general and localized, differential aeration), microbiologically influenced corrosion (MIC) and stray current corrosion, by DC and AC. For these last conditions, acceptance criteria of interference are highlighted.
Pietro Pedeferri (Deceased)

Chapter 22. Atmospheric Corrosion

Abstract
Metallic structures exposed to the atmosphere undergo corrosion when a thin liquid film forms at their surface. The extent of corrosion depends on chemical-physical properties of this film, hence on the parameters they are determined by, such as relative atmospheric humidity, temperature, composition as well as time of wetness. Many of these factors are difficult to quantify, and often have complex, contrasting effects on the corrosion process: this is the case of rain, wind and temperature. All of these factors are discussed in the chapter, together with the classification of atmospheric environments according to the ISO standards. The characteristics of most used metals are also reported with reference to their use in atmosphere.
Pietro Pedeferri (Deceased)

Chapter 23. Corrosion in Concrete

Abstract
This chapter deals with corrosion of rebars in concrete, specifying the types of corrosion forms with particular attention to the two most common ones, carbonation induced corrosion and chloride induced corrosion, due to the penetration in concrete of CO2 and chloride ions, respectively. Hydrogen embrittlement of high strength steels and stray current corrosion are also introduced. The preventative and protection methods that can be adopted are discussed, starting with concrete quality and dealing with additional protection methods, namely cathodic prevention, stainless steel and galvanised steel reinforcements, concrete coatings and corrosion inhibitors. Finally, an outline on inspection and diagnosis is presented.
Pietro Pedeferri (Deceased)

Chapter 24. Corrosion in Petrochemical Plant

Abstract
Production fluids extracted and transported in the oil and gas industry are multi-phase systems (oil, water and gas) with a variety of compositions. A necessary condition for corrosion is the metal wetting by an aqueous phase, which in turn depends on the fluid composition (water content) and on flow regime. If water wetting is effective on the metal surface, corrosiveness of the environment depends on its specific composition, for instance, on the presence or absence of CO2 and H2S in the gas phase, or oxygen in the liquid water phase that can accompany oil. The chapter deals with on corrosion problems concerning CO2 and H2S for both upstream, midstream and downstream, with a brief mention to some peculiar forms of corrosion occurring in the refinery plant. The behaviour of most relevant metals in the different environments is also summarized.
Pietro Pedeferri (Deceased)

Chapter 25. Corrosion in the Human Body

Abstract
Metallic materials can find many kinds of applications in the human body: for example, in orthopaedics, for hip and knee prostheses, for osteosynthesis devices, in the cardiovascular sector, for endovascular prostheses, cardiac valves, pace-makers; in stomatological areas and for osteointegrated dental implants. Herein, some corrosion problems linked to the metallic materials used in the human body are examined, focusing in particular on orthopaedic materials. Failure mechanisms of these materials is briefly revised, dealing with fatigue, general and localised corrosion, fretting. Finally, a brief outline of the surface finishing treatments is presented.
Pietro Pedeferri (Deceased)

Chapter 26. High Temperature Corrosion

Abstract
A metal in contact with a hot gas, typically at temperatures above 400 °C, in absence of liquid water phase, can suffer corrosion, also called hot corrosion. While aqueous (wet) corrosion processes are of electrochemical nature, hot corrosion is a chemical process, i.e., governed by chemical process kinetics in gas phase. Nevertheless, the oxide layer that forms at the metal surface is influenced by ionic diffusion and electronic conductivity within the oxide, as typical of an electrochemical mechanism. Corrosion attacks include: thinning due to the formation of non-protective scale, corrosion products and metal evaporation, metal degradation by molten salts, erosion-corrosion assisted by entrained solid particles, localized attack at grain boundaries, embrittlement. In this Chapter, the properties of oxides, as morphology, conductivity, protectiveness are described, together with the oxidation behaviour of metals and alloys; other processes (sulphidation, carburisation) and different environments, like steam and combustion gases, are briefly outlined.
Pietro Pedeferri (Deceased)

Chapter 27. Prevention of Corrosion in Design

Abstract
This chapter deals with the principles that should guide the design of a structure based on corrosion prevention. This includes a series of preventative measures that can be chosen once the environment and its criticalities are identified, as well as a careful metal selection. Information on the main classes of metallic alloys and their corrosion resistance are provided, as a help to guide the selection. The main preventative methods that should be adopted in the construction, storage and operating phases are also examined.
Pietro Pedeferri (Deceased)

Chapter 28. Monitoring and Inspections

Abstract
Corrosion of industrial equipment can lead to risk conditions for economic losses and safety of personnel. To minimize that risky, besides the correct selection of material and the use of proper preventative methods, the design of a corrosion monitoring system plays an important role, followed by programmed inspections during operation. The analysis of monitoring and inspection results is also important to plan maintenance activities. This Chapter deals with the selection of the correct monitoring strategy and its application to operating systems: the most common monitoring techniques, as the use of corrosion coupon, electrical probes, linear polarisation resistance, galvanic probes, corrosion potential are presented. A brief outline of the most important non-destructive techniques is also reported.
Pietro Pedeferri (Deceased)

Chapter 29. Testing

Abstract
Corrosion tests are an important instrument used to clarify the mechanisms of corrosion process, to develop new materials and new methods of protection, to carry out quality control tests, to follow the behaviour of materials in operation and, finally, when corrosion has occurred, to study the causes and the remedies. The classification of corrosion tests adopted in this chapter provides the division in two macro categories: exposure tests and electrochemical tests. This chapter wants to give some examples of the many possibilities of existing corrosion tests.
Pietro Pedeferri (Deceased)

Chapter 30. Statistical Analysis of Corrosion Data

Abstract
Statistical analysis—from data sampling to interpretation of results—is fundamental to all branches of science and engineering, as well as in the field of corrosion. Once corrosion data are obtained from testing (i.e. laboratory and/or field investigation), monitoring and inspection activities, statistical analysis can be very helpful to interpret such results, providing a rational, engineering approach. Nowadays, the amount of corrosion data has continuously increased. In spite of this, the statistical approach is not widely used in corrosion science and engineering even if proper methodologies are available to organize corrosion information and to improve industrial plant design and maintenance. In this chapter, the basic concepts of corrosion probability and statistical treatment of corrosion data are discussed. The chapter does not cover detailed description of statistical methods, rather considers a range of approaches with applications in corrosion testing.
Pietro Pedeferri (Deceased)

Backmatter

Additional information

Premium Partner

    Image Credits