Metal Corrosion - Causes and Types
John Poullain, P.E.
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.
At the conclusion of this course, the student will:
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.
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.
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.
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:
You need to open or download above documents to study this course.
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
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.
and Corrosion Control" by H. H. Uhlig, 3rd edition, Wiley
Why Metals Corrode