Corrosion engineering

Corrosion Engineering is the specialist discipline of applying scientific knowledge, natural laws and physical resources in order to design and implement materials, structures, devices, systems and procedures to manage the natural phenomenon known as corrosion. Generally related to Metallurgy or Materials Science, Corrosion Engineering also relates to non-metallics including ceramics, cement, and conductive materials such as carbon / 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 asset management. In the 1990s, Imperial College London even offered a Master of Science degree entitled "The Corrosion of Engineering Materials".

In the year 1995, it was reported that the costs nationwide in the U.S of corrosion were nearly $300 billion per year. [4]

Corrosion engineering groups have formed around the world in order to prevent, slow and manage the effects of corrosion. Examples of such groups are the National Association of Corrosion Engineers (NACE) and the European Federation of Corrosion (EFC), see Corrosion societies. The corrosion engineers main task is to economically and safely manage the effects of corrosion on materials. Corrosion Engineering master's degree courses are available worldwide and are concerned with the control and understanding of corrosion.

Zaki Ahmad in his book "Principles of corrosion engineering and corrosion control"(10)states that "Corrosion engineering is the application of the principles evolved from corrosion science to minimize or prevent corrosion. Corrosion engineering involves designing of corrosion prevention schemes and implementation of specific codes and practices. Corrosion prevention measures, like 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". In the "Handbook of corrosion engineering" (4) 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".

Most notable contributors to Corrosion Engineering education have been:

•Michael Faraday (1791–1867)

•Marcel Pourbaix (1904–1998)

•Melvin Romanoff

•Pierre R. Roberge

•Mars G. Fontana (1910–1988)

•Dr. Herbert H. Uhlig (1907–1993)

•Ulick Richardson Evans (1889–1980)

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 environments. And nothing survives well in high sulfide and low redox potential environments with corrosive bacteria.

External corroding

Underground soil side corrosion

Underground corrosion control engineers will collect soil samples to test soil chemistry for corrosive factors such as pH, minimum soil resistivity, chlorides, sulfates, ammonia, nitrates, sulfide, and redox potential. The soil samples are collected from the depth from which the infrastructure will be installed because soil properties can change from strata to strata. The minimum test of in-situ soil resistivity is measured using the Wenner 4 pin method if often performed to judge a site's corrosivity, but if the test is performed during a dry period, the soil's actual corrosivity may not be properly reported since underground condensation can occur on buried metals leaving the soil touching the metal surfaces in a more moist status. This is why measuring a soil's minimum or saturated resistivity is so important. Soil resistivity testing alone will also not identify corrosive elements.^[1] 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.

Geotechnical engineers typically do not practice corrosion engineering and will refer their clients to a corrosion engineer if the soil resistivity is measured to be below 3,000 ohm-cm or less depending which soil corrosivity categorization table they are reading. Unfortunately, an old dairy farm can have soil resistivities above 3,000 ohm-cm and still contain corrosive ammonia and nitrate levels which will lead to corrosion of 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 will 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.

Atmospheric corrosion

Atmospheric corrosion is typically handled by use of materials selection and coatings specifications. The use of zinc coatings also known as galvanizing on steel structures is a form of cathodic protection in which small scratches are expected to occur in the coating over time. 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 with the moisture, but if the scratch or uncoated area is larger than the droplets, then corrosion can occur. As long as there is moisture, the zinc will corrode and eventually disappear.

Humid and splash zone corrosion

'Pile jackets' encasing old concrete bridge pilings to combat the corrosion that occurs when cracks in the pilings allow saltwater to contact internal steel reinforcement rods

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 your 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 which has a lot of oxygen and agitation that can remove 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.

References

(1) Corrosion for students of science and engineering Tretheway K R & Chamberlain J

(2) Corrosion Vols 1 and 2 Metal Environment Reactions, Edited by L. L. Shrier Pub Butterworth-Heinemann Ltd

(3) Corrosion engineering Mars Guy Fontana McGraw-Hill, 1986

(4) Handbook of corrosion engineering By Pierre R. Roberge

(5) Corrosion engineering: principles and practice Pierre R. Roberge McGraw-Hill Prof Med/Tech, 2008

(6) The Corrosion Handbook, Uhlig, H. H. (Ed.), Wiley, New York and Chapman and Hall, London (1948)

(7) Corrosion and Corrosion Control, Uhlig, H. H., Wiley, New York (1971)

(8) Corrosion Engineering, Fontana, M. G. and Greene, N. D., McGraw-Hill (1967)

(10) Principles of corrosion engineering and corrosion control Zaki Ahmad, Institution of Chemical Engineers (Great Britain)

(11) Corrosion Engineering by Volkan Cicek (Author) Publisher: Wiley-Scrivener; 1 edition (2 April 2014) Inc.ASIN: B00JJUL8LC

(12) Corrosion Engineering: Principles and Practice [Kindle Edition] Pierre Roberge (Author) Publisher: McGraw-Hill Professional; 1 edition (25 March 2008) ASIN: B0018G4HEK

External links

Wikimedia Commons has media related to Corrosion.

• NACE (formerly known as the National Association of Corrosion Engineers).NACE International NACE
• European Federation of Corrosion http://www.efcweb.org/