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Metal Corrosion - Causes and Types

John Poullain, P.E.

Course Outline

This one-hour online course discusses the causes and types of metal corrosion and methods available to mitigate corrosion. Proper handling and connections of metal can avoid the conditions that tend to promote corrosion. Basic methods used to mitigate corrosion such as design considerations, cathodic protection, protective coatings and inhibitors are briefly discussed. Repair and rehabilitation of corroded surfaces are not discussed here.

This 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:

Intended Audience

This course is intended for civil engineers, planners and contractors.

Benefit to Attendees

The student will become familiar with the basic theory and causes of corrosion and the methods and materials commonly used to mitigate corrosion. Components necessary for corrosion, anode, cathode, electrolyte and electrical current are discussed. The student will also have an understanding of the types of corrosion and the galvanic series of metals. Methods used to prevent corrosion for the types of corrosion are described. Advantages of the methods and materials used for mitigation are briefly discussed.

Course Introduction

This course deals primarily with the causes of corrosion of metals. Other materials however will also corrode when exposed to certain environments. Alkaline solutions can corrode glass and sulfate groundwater can corrode concrete. Aluminum, lead and zinc are subject to corrosion but are protected to an extent by the oxide films that develop on the surface. Bacteria are also agents of metal corrosion particularly on metals containing iron.

The annual cost of corrosion in the US is estimated to be in the billions of dollars. Corrosion is the destruction of a metal by electrochemical reaction with its environment and specifically applies to the action of agents such as air or water on metals. For corrosion to take place these three conditions must exist:

1. An anode and cathode - this will occur when two dissimilar metals or two regions of differential electrolyte concentration create a difference in electrical potential.
2. A metallic connector between the anode and cathode.
3. An electrolyte such as water ( environment)

Eliminating these three conditions may not always be feasible or practical. Dissimilar metal contact for instance cannot always be avoided but corrosion can be minimized by such measures as surface treatments, plating, painting, sealing and design practices. Water may not be avoided but it can be controlled with drainholes, sealents and inhibitors. This is a problem dealt with in the airplane industry where dissimilar metals cannot be avoided because of weight factors and water is one of the biggest corrosion problems.

Water control may be the best means for corrosion prevention in many areas. Moisture and water are especially corrosive for concrete structures. Reinforced concrete bridges, dams, piers and industrial facilities are under attack and destroyed without corrosion control. Steel reinforcement is subjected to corrosion after chloride and carbonation disrupts the natural passive protection. Certain coating form a protective layer on the steel.

Course Content

This course is based on Chapter 2 of the US Army Corps of Engineers Manual, "Painting: New Construction and Maintenance", EM 1110-2-3400 (1995 Edition, 8 pages), PDF file.
The course is also based on Chapter 2, "Causes of Structural deterioration" of the US Army Corps of Engineers Manual EM 1110-2-6054 (2001 Edition, 2 pages)

The link to the above course materials are:

The US Army Corps of Engineers Manual, "Painting: New Construction and Maintenance", EM 1110-2-3400 - Chapter 2 (1995 Edition, 8 pages)

The US Army Corps of Engineers Manual, "Causes of Structural deterioration", EM 1110-2-6054 - Chapter 2 (2001 Edition, 2 pages)

You need to open or download above documents to study this course.

Course Summary

This course considers the electrochemical causes of metal corrosion and components required for corrosion to take place, anode-cathode, electrolyte and anode to cathode connectors are discussed. The galvanic series of metals, the metals position and the possibility under certain conditions of reversing positions between active and passive states are discussed. The types of corrosion and condition causing the different types of corrosion are presented. Methods for mitigating corrosion are briefly discussed since it is not always practical or feasible to eliminate the conditions causing corrosion.

Related Links

For additional technical information related to this subject, please refer to:
The technology for reduction of rusting, treatment methods and theory of corrosion.
Corrosion, electrochemical theory, resistance to corrosion, treatments such as cathodic protection, seals and paints are described.
Paints, coatings metal alloys and various problem areas are discussed.

"Corrosion and Corrosion Control" by H. H. Uhlig, 3rd edition, Wiley

Why Metals Corrode


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.