Basic Overview of Corrosion Theory - a PDH Online Course for Engineers

Basic Overview of Corrosion Theory

Course Outline

Corrosion is the primary means by which metals deteriorate. Most metals corrode on contact with water (and moisture in the air), acids, bases, salts, oils, aggressive metal polishes, and other solid and liquid chemicals. The objective of this course is to introduce the readers to the underlying science of corrosion engineering principles developed from thermodynamic, kinetic, mass transfer and potential theory.

This 2-hour course material is based entirely on US Department of Energy training materials DOE-HDBK-1015/1-92, Fundamentals Handbook, Chemistry, Module 2, and Volume 1 of 2

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will:

Develop a sound understanding of corrosion theory and applications;
Understand the basic types and mechanisms of corrosion;
Understand what happens to metal during the reduction step of the oxidation-reduction process;
Describe the affects of passivity and polarization on the corrosion process;
Learn the engineering design of corrosion prevention systems; and
Understand the conditions necessary for stress corrosion to occur.

Intended Audience

This course is aimed at students, mechanical, material science and process engineers, contractors, estimators, energy auditors, safety personnel, plant layout professionals and general audience.

Course Introduction

Corrosion specifically refers to any process involving the deterioration or degradation of metal components. The best known case is that of the rusting of steel. Corrosion processes are usually electrochemical in nature, having the essential features of a battery. When metal atoms are exposed to an environment containing water molecules they can give up electrons, becoming themselves positively charged ions, provided an electrical circuit can be completed. This effect can be concentrated locally to form a pit or, sometimes, a crack, or it can extend across a wide area to produce general wastage.

Course Content

In this course, you are required to study following US Department of Energy training materials:

The DOE-HDBK-1015/1-92, Fundamentals Handbook, Chemistry, Module 2, and Volume 1 of 2

You need to open or download this document to study this course.

Course Summary

Corrosion is the disintegration of metal through an unintentional chemical or electrochemical action, starting at its surface. All metals exhibit a tendency to be oxidized, some more easily than others. A tabulation of the relative strength of this tendency is called the galvanic series. Knowledge of a metal's location in the series is an important piece of information to have in making decisions about its potential usefulness for structural and other applications.

The corrosion process is an anodic reaction of the metal dissolving as ions. The process generates some electrons, which are consumed by a secondary process (cathodic reaction) in close proximity to the corrosion reaction itself. The electrons and the hydrogen ions react to first form atomic hydrogen, and then molecular hydrogen gas. As hydrogen forms, it will inhibit further corrosion by forming a very thin gaseous film at the surface of the metal. This "polarizing" film is effective in reducing water to metal contact and thus reducing corrosion. Anything which breaks down this barrier film will tend to increase the rate of corrosion. Dissolved oxygen in the water will react with the hydrogen, converting it to water, and destroying the film.

variety of natural and environmental factors can have significant effects on the corrosion rate of metals. These include:

High water velocities tend to sweep the film away, exposing fresh metal to the water
Solid particles in the water can brush the hydrogen film from the metal
High concentrations of free hydrogen ions (low pH) speed the release of the electrons
High water temperatures, increase virtually all chemical reaction rates

All the above factors accelerate the corrosion process even when no other special conditions are involved.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.