Corrosion is the destructive attack of a material by reaction with its
environment. The serious consequences of the corrosion process have
become a problem of worldwide significance. In addition to our everyday
encounters with this form of degradation, corrosion causes plant
shutdowns, waste of valuable resources, loss or contamination of product,
reduction in efficiency, costly maintenance, and expensive overdesign;
it also jeopardizes safety and inhibits technological progress.
The multidisciplinary aspect of corrosion problems combined with the
distributed responsibilities associated with such problems only
increase the complexity of the subject. Corrosion control is achieved by
recognizing and understanding corrosion mechanisms, by using corrosion-
resistant materials and designs, and by using protective systems,
devices, and treatments. Major corporations, industries, and government
agencies have established groups and committees to look after
corrosion-related issues, but in many cases the responsibilities are
spread between the manufacturers or producers of systems and their
users. Such a situation can easily breed negligence and be quite costly
in terms of dollars and human lives.
I.1 The Cost of Corrosion
Although the costs attributed to corrosion damages of all kinds have
been estimated to be of the order of 3 to 5 percent of industrialized
countries’ gross national product (GNP), the responsibilities associated
with these problems are sometimes quite diffuse. Since the first significant
report by Uhlig1 in 1949 that the cost of corrosion to nations
is indeed great, the conclusion of all subsequent studies has been that
corrosion represents a constant charge to a nation’s GNP.2 One conclusion
of the 1971 UK government-sponsored report chaired by Hoar3
was that a good fraction of corrosion failures were avoidable and that
improved education was a good way of tackling corrosion avoidance.
Corrosion of metals cost the U.S. economy almost $300 billion per
year at 1995 prices.4 Broader application of corrosion-resistant materials
and the application of the best corrosion-related technical practices
could reduce approximately one-third of these costs. These
estimates result from a recent update by Battelle scientists of an earlier
study reported in 1978.5 The initial work, based upon an elaborate
model of more than 130 economic sectors, had revealed that metallic
corrosion cost the United States $82 billion in 1975, or 4.9 percent of
its GNP. It was also found that 60 percent of that cost was unavoidable.
The remaining $33 billion (40 percent) was said to be “avoidable”
and incurred by failure to use the best practices then known.
In the original Battelle study, almost 40 percent of 1975 metallic corrosion
costs were attributed to the production, use, and maintenance
of motor vehicles. No other sector accounted for as much as 4 percent
of the total, and most sectors contributed less than 1 percent. The 1995
Battelle study indicated that the motor vehicles sector probably had
made the greatest anticorrosion effort of any single industry. Advances
have been made in the use of stainless steels, coated metals, and more
protective finishes. Moreover, several substitutions of materials made
primarily for reasons of weight reduction have also reduced corrosion.
Also, the panel estimated that 15 percent of previously unavoidable
corrosion costs can be reclassified as avoidable. The industry is estimated
to have eliminated some 35 percent of its “avoidable” corrosion
by its improved practices. Table I.1 summarizes the costs attributed to
metallic corrosion in the United States in these two studies.
I.2 Examples of Catastrophic
Corrosion Damage
I.2.1 Sewer explosion, Mexico
An example of corrosion damages with shared responsibilities was the
sewer explosion that killed over 200 people in Guadalajara, Mexico, in
April 1992.6 Besides the fatalities, the series of blasts damaged 1600
buildings and injured 1500 people. Damage costs were estimated at 75
million U.S. dollars. The sewer explosion was traced to the installation
of a water pipe by a contractor several years before the explosion that
leaked water on a gasoline line laying underneath. The subsequent
corrosion of the gasoline pipeline, in turn, caused leakage of gasoline
into the sewers. The Mexican attorney general sought negligent homicide
charges against four officials of Pemex, the government-owned oil
company. Also cited were three representatives of the regional sewer
system and the city’s mayor.
I.2.2 Loss of USAF F16 fighter aircraft
This example illustrates a case that has recently created problems in
the fleet of USAF F16 fighter aircraft. Graphite-containing grease is a
very common lubricant because graphite is readily available from steel
industries. The alternative, a formulation containing molybdenum
disulphide, is much more expensive. Unfortunately, graphite grease is
well known to cause galvanically induced corrosion in bimetallic couples.
In a fleet of over 3000 F16 USAF single-engine fighter aircraft,
graphite grease was used by a contractor despite a general order from
the Air Force banning its use in aircraft.7 As the flaps were operated,
lubricant was extruded into a part of the aircraft where control of the
fuel line shutoff valve was by means of electrical connectors made from
a combination of gold- and tin-plated steel pins. In many instances corrosion
occurred between these metals and caused loss of control of the
valve, which shut off fuel to the engine in midflight. At least seven aircraft
are believed to have been lost in this way, besides a multitude of
other near accidents and enormous additional maintenance.
I.2.3 The Aloha aircraft incident
The structural failure on April 28, 1988, of a 19-year-old Boeing 737,
operated by Aloha airlines, was a defining event in creating awareness
of aging aircraft in both the public domain and in the aviation community.
This aircraft lost a major portion of the upper fuselage near the
front of the plane in full flight at 24,000 ft.8 Miraculously, the pilot managed
to land the plane on the island of Maui, Hawaii. One flight attendant
was swept to her death. Multiple fatigue cracks were detected
in the remaining aircraft structure, in the holes of the upper row of rivets
in several fuselage skin lap joints. Lap joints join large panels of
skin together and run longitudinally along the fuselage. Fatigue cracking
was not anticipated to be a problem, provided the overlapping panels
remained strongly bonded together. Inspection of other similar
aircraft revealed disbonding, corrosion, and cracking problems in the
lap joints. Corrosion processes and the subsequent buildup of voluminous
corrosion products inside the lap joints, lead to “pillowing,” whereby
the faying surfaces are separated. Special instrumentation has been
developed to detect this dangerous condition. The aging aircraft problem
will not go away, even if airlines were to order unprecedented numbers
of new aircraft. Older planes are seldom scrapped, and the older
planes that are replaced by some operators will probably end up in service
with another operator. Therefore, safety issues regarding aging
aircraft need to be well understood, and safety programs need to be
applied on a consistent and rigorous basis.
I.2.4 The MV KIRKI
Another example of major losses to corrosion that could have been prevented
and that was brought to public attention on numerous occasions
since the 1960s is related to the design, construction, and
operating practices of bulk carriers. In 1991 over 44 large bulk carriers
were either lost or critically damaged and over 120 seamen lost
their lives.9 A highly visible case was the MV KIRKI, built in Spain in
1969 to Danish designs. In 1990, while operating off the coast of
Australia, the complete bow section became detached from the vessel.
Miraculously, no lives were lost, there was little pollution, and the vessel
was salvaged. Throughout this period it seems to have been common
practice to use neither coatings nor cathodic protection inside
ballast tanks. Not surprisingly therefore, evidence was produced that
serious corrosion had greatly reduced the thickness of the plate and
that this, combined with poor design to fatigue loading, were the primary
cause of the failure. The case led to an Australian Government
report called “Ships of Shame.” MV KIRKI is not an isolated case.
There have been many others involving large catastrophic failures,
although in many cases there is little or no hard evidence when the
ships go to the bottom.
I.2.5 Corrosion of the infrastructure
One of the most evident modern corrosion disasters is the present state
of degradation of the North American infrastructure, particularly in
the snow belt where the use of road deicing salts rose from 0.6M ton in
1950 to 10.5M tons in 1988. The structural integrity of thousands of
bridges, roadbeds, overpasses, and other concrete structures has been
impaired by corrosion, urgently requiring expensive repairs to ensure
public safety. A report by the New York Department of Transport has
stated that, by 2010, 95 percent of all New York bridges would be deficient
if maintenance remained at the same level as it was in 1981.
Rehabilitation of such bridges has become an important engineering
practice.10 But the problems of corroding reinforced concrete extend
much beyond the transportation infrastructure. A survey of collapsed
buildings during the 1974 to 1978 period in England showed that the
immediate cause of failure of at least eight structures, which were 12
to 40 years old, was corrosion of reinforcing or prestressing steel.
Deterioration of parking garages has become a major concern in
Canada. Of the 215 garages surveyed recently, almost all suffered varying
degrees of deterioration due to reinforcement corrosion, which was
a result of design and construction practices that fell short of those
required by the environment. It is also stated that almost all garages
in Canada built until very recently by conventional methods will
require rehabilitation at a cost to exceed $3 billion. The problem surely
extends to the northern United States. In New York, for example, the
seriousness of the corrosion problem of parking garages was revealed
dramatically during the investigation that followed the bomb attack on
the underground parking garage of the World Trade Center.
