Corrosion engineering is an engineering specialty that applies scientific, technical, engineering skills, and knowledge of natural laws and physical resources to design and implement materials, structures, devices, systems, and procedures to manage corrosion. From a holistic perspective, corrosion is the phenomenon of metals returning to the state they are found in nature. The driving force that causes metals to corrode is a consequence of their temporary existence in metallic form. To produce metals starting from naturally occurring minerals and ores, it is necessary to provide a certain amount of energy, e.g. Iron ore in a blast furnace. It is therefore thermodynamically inevitable that these metals when exposed to various environments would revert to their state found in nature. Corrosion and corrosion engineering thus involves a study of chemical kinetics, thermodynamics, electrochemistry and materials science.
General background
Generally related to metallurgy or materials science, corrosion engineering also relates to non-metallics including ceramics, cement, composite material, and conductive materials such as carbon and graphite. Corrosion engineers often manage other not-strictly-corrosion processes including (but not restricted to) cracking, brittle fracture, crazing, fretting, erosion, and more typically categorized as Infrastructure asset management. In the 1990s, Imperial College London even offered a Master of Science degree entitled "The Corrosion of Engineering Materials". UMIST – University of Manchester Institute of Science and Technology and now part of the University of Manchester also offered a similar course. Corrosion Engineering master's degree courses are available worldwide and the curricula contain study material about the control and understanding of corrosion. Ohio State University has a corrosion center named after one of the more well known corrosion engineers Mars G Fontana.
Corrosion costs
In the year 1995, it was reported that the costs of corrosion nationwide in the United States were nearly $300 billion per year. This confirmed earlier reports of damage to the world economy caused by corrosion.
Zaki Ahmad, in his book Principles of corrosion engineering and corrosion control, states that "Corrosion engineering is the application of the principles evolved from corrosion science to minimize or prevent corrosion". Shreir et al. suggest likewise in their large, two volume work entitled Corrosion. Corrosion engineering involves designing of corrosion prevention schemes and implementation of specific codes and practices. Corrosion prevention measures, including Cathodic protection, designing to prevent corrosion and coating of structures fall within the regime of corrosion engineering. However, corrosion science and engineering go hand-in-hand and they cannot be separated: it is a permanent marriage to produce new and better methods of protection from time to time. This may include the use of Corrosion inhibitors. In the Handbook of corrosion engineering, the author Pierre R. Roberge states "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."
Costs are not only monetary. There is a financial cost and also a waste of natural resources. In 1988 it was estimated that one tonne of metal was converted completely to rust every ninety seconds in the United Kingdom. There is also the cost of human lives. Failure whether catastrophic or otherwise due to corrosion has cost human lives.
Corrosion engineering and corrosion societies and associations
Corrosion engineering groups have formed around the world to educate, prevent, slow, and manage corrosion. These include the National Association of Corrosion Engineers (NACE), the European Federation of Corrosion (EFC), and the Australasian Corrosion Association. The corrosion engineer's main task is to economically and safely manage the effects of corrosion of materials.
Notable contributors to the field
Some of the most notable contributors to the Corrosion Engineering discipline include among others:
Michael Faraday (1791–1867) Marcel Pourbaix (1904–1998) Herbert H. Uhlig (1907–1993) Ulick Richardson Evans (1889–1980) Mars Guy Fontana (1910–1988) Melvin Romanoff ( -1970)
Types of corrosion situations Corrosion engineers and consultants tend to specialize in Internal or External corrosion scenarios. In both, they may provide corrosion control recommendations, failure analysis investigations, sell corrosion control products, or provide installation or design of corrosion control and monitoring systems. Every material has its weakness. Aluminum, galvanized/zinc coatings, brass, and copper do not survive well in very alkaline or very acidic pH environments. Copper and brasses do not survive well in high nitrate or ammonia environments. Carbon steels and iron do not survive well in low soil resistivity and high chloride environments. High chloride environments can even overcome and attack steel encased in normally protective concrete. Concrete does not survive well in high sulfate and acidic environments. And nothing survives well in high sulfide and low redox potential environments with corrosive bacteria. This is called Biogenic sulfide corrosion.
External corrosion
Underground soil side corrosion Underground corrosion control engineers collect soil samples to test soil chemistry for corrosive factors such as pH, minimum soil resistivity, chlorides, sulfates, ammonia, nitrates, sulfide, and redox potential. They collect samples from the depth that infrastructure will occupy, because soil properties may change from strata to strata. The minimum test of in-situ soil resistivity is measured using the Wenner four pin method if often performed to judge a site's corrosivity. However, during a dry period, the test may not show actual corrosivity, since underground condensation can leave soil in contact with buried metal surfaces more moist. This is why measuring a soil's minimum or saturated resistivity is important. Soil resistivity testing alone does not identify corrosive elements. Corrosion engineers can investigate locations experiencing active corrosion using above ground survey methods and design corrosion control systems such as cathodic protection to stop or reduce the rate of corrosion.OFFICIAL EXHIBIT – ENT000391-00-BD01 – M. Romanoff, Underground Corrosion, National Bureau of Standards Circular (1957). (nrc.gov)
Geotechnical engineers typically do not practice corrosion engineering, and refer clients to a corrosion engineer if soil resistivity is below 3,000 ohm-cm or less, depending the soil corrosivity categorization table they read. Unfortunately, an old dairy farm can have soil resistivities above 3,000 ohm-cm and still contain corrosive ammonia and nitrate levels that corrode copper piping or grounding rods. A general saying about corrosion is, "If the soil is great for farming, it is great for corrosion."
Underwater external corrosion Underwater corrosion engineers apply the same principals used in underground corrosion control but use specially trained and certified scuba divers for condition assessment, and corrosion control system installation and commissioning. The main difference being in the type of reference cells used to collect voltage readings. Corrosion of piles and the legs of oil and gas rigs are of particular concern. This includes rigs in the North Sea off the coast of the United Kingdom and the Gulf of Mexico.
Atmospheric corrosion Atmospheric corrosion generally refers to general corrosion in a non-specific environment. Prevention of atmospheric corrosion is typically handled by use of materials selection and coatings specifications. The use of zinc coatings also known as galvanization on steel structures is a form of cathodic protection where the zinc acts as a sacrificial anode and also a form of coating. Small scratches are expected to occur in the galvanized coating over time. The zinc being more active in the galvanic series corrodes in preference to the underlying steel and the corrosion products fil the scratch preventing further corrosion. As long as the scratches are fine, condensation moisture should not corrode the underlying steel as long as both the zinc and steel are in contact. As long as there is moisture, the zinc corrodes and eventually disappears. Impressed current cathodic protection is also used.
Splash zone and water spray corrosion
The usual definition of a splash zone is the area just above and just below the average water level of a body of water. It also includes areas that may be subject to water spray and mist.Creamer E.V. "Splash Zone Protection of Marine Structures" Paper number 1274, Offshore Technology Conference, Houston TX, 1970
A significant amount of corrosion of fences is due to landscaper tools scratching fence coatings and irrigation sprinklers spraying these damaged fences. Recycled water typically has a higher salt content than potable drinking water, meaning that it is more corrosive than regular tap water. The same risk from damage and water spray exists for above ground piping and backflow preventers. Fiberglass covers, cages, and concrete footings have worked well to keep tools at an arm's length. Even the location where a roof drain splashes down can matter. Drainage from a home's roof valley can fall directly down onto a gas meter causing its piping to corrode at an accelerated rate reaching 50% wall thickness within 4 years. It is the same effect as a splash zone in the ocean, or in a pool with lot of oxygen and agitation that removes material as it corrodes.
Tanks or structural tubing such as bench seat supports or amusement park rides can accumulate water and moisture if the structure does not allow for drainage. This humid environment can then lead to internal corrosion of the structure affecting the structural integrity. The same can happen in tropical environments leading to external corrosion. This would include Corrosion in ballast tanks on ships.
Pipeline corrosion Hazardous materials are often carried in pipelines and thus their structural integrity is of paramount importance. Corrosion of a pipeline can thus have grave consequences.Control of Pipeline Corrosion A.W.Peabody published 1967 NACE Library of Congress catalog number 76-27507 One of the methods used to control pipeline corrosion is by the use of Fusion bonded epoxy coatings. DCVG is used to monitor it. Impressed current cathodic protection is also used.
Corrosion in the petrochemical industry The Petrochemical industry typically encounters aggressive corrosive media. These include sulfides and high temperatures. Corrosion control and solutions are thus necessary for the world economy. Scale formation in injection water presents its own problems with regard to corrosion and thus for the corrosion engineer.
Corrosion in ballast tanks
Ballast tanks on ships contain the fuels for corrosion. Water is one and air is usually present too and the water can become stagnant. Structural integrity is important for safety and to avoid marine pollution. Coatings have become the solution of choice to reduce the amount of corrosion in ballast tanks. Impressed current cathodic protection has also been used. Likewise sacrificial anode cathodic protection is also used. Since chlorides vastly accelerate corrosion, ballast tanks of marine vessels are particularly susceptible.
Corrosion in the railway industry