Principles of Corrosion Engineering and Corrosion Control

Zaki Ahmad

• Publisher: Butterworth-Heinemann
• Year: 2006
• ISBN:
  9780080480336
• Topic: Technology & Engineering
• Subtopic: Mining Engineering
• Index: Technology & Engineering

Corrosion is a huge issue for materials, mechanical, civil and petrochemical engineers. With comprehensive coverage of the principles of corrosion engineering, this book is a one-stop text and reference for students and practicing corrosion engineers. Highly illustrated, with worked examples and definitions, it covers basic corrosion principles, and more advanced information for postgraduate students and professionals. Basic principles of electrochemistry and chemical thermodynamics are incorporated to make the book accessible for students and engineers who do not have prior knowledge of this area. Each form of corrosion covered in the book has a definition, description, mechanism, examples and preventative methods. Case histories of failure are cited for each form. End of chapter questions are accompanied by an online solutions manual.* Comprehensively covers the principles of corrosion engineering, methods of corrosion protection and corrosion processes and control in selected engineering environments* Structured for corrosion science and engineering classes at senior undergraduate and graduate level, and is an ideal reference that readers will want to use in their professional work* Worked examples, extensive end of chapter exercises and accompanying online solutions and written by an expert from a key pretochemical university

CHAPTER 1

INTRODUCTION TO CORROSION

Publisher Summary

This chapter describes corrosion. The term “corrosion” now encompasses all types of natural and man-made materials, including biomaterials and nanomaterials, and it is not confined to metals and alloys alone. The chapter also discusses the historical background of corrosion. Corrosion cannot be defined without a reference to environment. All environments are corrosive to some degree. The chapter discusses the consequences and costs of corrosion. Corrosion has a serious impact on defense equipment. The petroleum, chemical, petrochemical, construction, manufacturing, pulp and paper, and transportation (railroad, automotive, and aerospace) industries are the largest contributors to corrosion expenditure. The cost of corrosion differs from country to country..Corrosion engineering is the application of principles evolved from corrosion science to minimize or prevent corrosion. Corrosion engineering involves designing of corrosion-prevention schemes and implementation of specific codes and practices. Corrosion may severely affect the functions of metals, plants, and equipment. The chapter also discusses the health hazard involved with corroded structures.

1.1 HISTORICAL BACKGROUND

’Lay not up for yourselves treasures upon earth where moth and rust doth corrupt and where thieves breakthrough and steal.’

(Mathew 6:14)

The word corrosion is as old as the earth, but it has been known by different names. Corrosion is known commonly as rust, an undesirable phenomena which destroys the luster and beauty of objects and shortens their life. A Roman philosopher, Pliny (AD 23–79) wrote about the destruction of iron in his essay ‘Ferrum Corrumpitar.’ Corrosion since ancient times has affected not only the quality of daily lives of people, but also their technical progress. There is a historical record of observation of corrosion by several writers, philosophers and scientists, but there was little curiosity regarding the causes and mechanism of corrosion until Robert Boyle wrote his ‘Mechanical Origin of Corrosiveness.’

Philosophers, writers and scientists observed corrosion and mentioned it in their writings:

Pliny the elder (AD 23–79) wrote about spoiled iron.

Herodotus (fifth century BC) suggested the use of tin for protection of iron.

Lomonosov (1743–1756).

Austin (1788) noticed that neutral water becomes alkaline when it acts on iron.

Thenard (1819) suggested that corrosion is an electrochemical phenomenon.

Hall (1829) established that iron does not rust in the absence of oxygen.

Davy (1824) proposed a method for sacrificial protection of iron by zinc.

De la Rive (1830) suggested the existence of microcells on the surface of zinc.

The most important contributions were later made by Faraday (1791–1867) [1] who established a quantitative relationship between chemical action and electric current. Faraday’s first and second laws are the basis for calculation of corrosion rates of metals. Ideas on corrosion control started to be generated at the beginning of nineteenth century. Whitney (1903) provided a scientific basis for corrosion control based on electrochemical observation. As early as in eighteenth century it was observed that iron corrodes rapidly in dilute nitric acid but remains unattacked in concentrated nitric acid. Schönbein in 1836 showed that iron could be made passive [2]. It was left to U. R. Evans to provide a modern understanding of the causes and control of corrosion based on his classical electrochemical theory in 1923. Considerable progress towards the modern understanding of corrosion was made by the contributions of Evans [3], Uhlig [4] and Fontana [5]. The above pioneers of modern corrosion have been identified with their well known books in the references given at the end of the chapter. Corrosion laboratories established in M.I.T., USA and University of Cambridge, UK, contributed significantly to the growth and development of corrosion science and technology as a multi disciplinary subject. In recent years, corrosion science and engineering has become an integral part of engineering education globally.

1.2 DEFINITIONS

Corrosion is a natural and costly process of destruction like earthquakes, tornados, floods and volcanic eruptions, with one major difference. Whereas we can be only a silent spectator to the above processes of destruction, corrosion can be prevented or at least controlled. Several definitions of corrosion have been given and some of them are reproduced below:

(A) Corrosion is the surface wastage that occurs when metals are exposed to reactive environments.

(B) Corrosion is the result of interaction between a metal and environments which results in its gradual destruction.

(C) Corrosion is an aspect of the decay of materials by chemical or biological agents.

(D) Corrosion is an extractive metallurgy in reverse. For instance, iron is made from hematite by heating with carbon. Iron corrodes and reverts to rust, thus completing its life cycle. The hematite and rust have the same composition (Fig. 1.1).

Figure 1.1 Refining-corrosion cycle

(E) Corrosion is the deterioration of materials as a result of reaction with its environment (Fontana).

(F) Corrosion is the destructive attack of a metal by chemical or electrochemical reaction with the environment (Uhlig).

Despite different definitions, it can be observed that corrosion is basically the result of interaction between materials and their environment. Up to the 1960s, the term corrosion was restricted only to metals and their alloys and it did not incorporate ceramics, polymers, composites and semiconductors in its regime. The term corrosio...