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. 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.
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. 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.
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.
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. 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.
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. 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
Fontes:
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