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The formation of a monomolecular layer of a compound between the metal's surface atoms. This layer separates the metal's atoms thereby weakening the metal and allowing any existing defects to propagate when a stress is applied.
Chemisorption
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What is stainless steel’s biggest vulnerability at a plant (type of corrosion)
Chloride stress corrosion is a particularly significant problem in the operation of nuclear plants and industrial facilities using austenitic stainless steel under high tensile stress associated with pressurization
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Describe pitting corrosion
A type of corrosion that occurs when a small anodic site becomes fixed in a small area and the formation of holes (deep attack) in an otherwise unaffected area takes place
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Describe Caustic stress corrosion
Caustic stress corrosion, or caustic embrittlement, is another form of intergranular corrosion cracking. The mechanism is similar to that of chloride stress corrosion. Mild steels (steels with low carbon and low alloy content) and stainless steels will crack if they are exposed to concentrated caustic (high pH) environments with the metal under a tensile stress
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List the effects of corrosion
- Leaks in the RCS
- Leak in the Fuel Cladding
- Radioactive material created from corrosion
- Fouling
- Component Wear
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List the causes of corrosion
- Effective electrode potential of a metal in a solution
- Overvoltage of hydrogen on the metal
- Chemical and physical homogeneity of the metal surface
- Inherent ability to form an insoluble protective film
Influence of oxygen in solution adjacent to the metal
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Compare hematite and magnetite as well as their properties
- HEM = Fe2O3 - mineral form of iron - black in color has a rust red streak - trigonal - hexagonal
- MAG = Fe3O4 - octcahedral - black grey with brownish tint 1 part wustite 1 part hematite
Note wustite is FeO which is also called IronOxide
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What are the two conditions that contribute to General Corrosion
- Metal & Water in the same enviroment
- A chemical reaction between the metal and water that forms oxide
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Describe general corrosion
General corrosion is the process whereby the surface of a metal undergoes a slow, relatively uniform, removal of material
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Describe Galvanic corrosion
Galvanic corrosion is the corrosion that results when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte
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Define Oxidation
Oxidation occurs at the anode and it means the giving up of electrons (up the wire)
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Define Reduction
Reduction occurs at the cathode and it means the taking on of electrons (from the wire)
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What type of corrosion results from the presence of elevated oxygen
General Corrosion
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Explain the use of Cathodic Protection
- Electricity, Zinc
- The use of cathodic protection, supplying an external electric current to the iron so that it acts as a cathode and has no anodic areas, is another method of preventative chemical control. This can be accomplished by the use of an external voltage source or by the use of a sacrificial anode (e.g., zinc), a more reactive metal. The sacrificial anode undergoes an oxidation reaction more readily than the metal to be protected
- Helps prevent Galvanic and General Corrosion
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Discuss the corrosion activation cycle or CRUD cycle
- Peroxide is added to the reactor coolant during let down to the CVCS system.
- The CRUD or Chalk River Unidentified Deposits is filtered by demins
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A measure of the ability of a substance to allow electron flow
Conductivity
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The deterioration of a material due to interaction with its environment
Corrosion
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A type of localized pitting corrosion that occurs specifically within the low flow region of a crevice.
Crevice corrosion
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Corrosion and wear products in the form of finely divided, insoluble oxide particles suspended in the reactor coolant or loosely adhered to metal surfaces or activated corrosion and wear products
Crud
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Decomposition by electric current
Electrolysis
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A type of corrosion that results when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte
Galvanic corrosion
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A type of corrosion process whereby the surface of a metal undergoes a slow, relatively uniform, removal of material
General corrosion
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The process of adding electrons to or removing electrons from atoms or molecules that creates ions
Ionization
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The buildup of a stable, tenacious layer of metal oxide on the surface of the metal that acts as a barrier separating the metal surface from the environment.
Passivity
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A type of corrosion that occurs when a small anodic site becomes fixed in a small area and the formation of holes (deep attack) in an otherwise unaffected area takes place
Pitting corrosion
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A decrease in cell potential caused by the operation of an electrochemical cell.
Polarization
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The deposition on the surfaces of the piping from the formation of insoluble compounds from normally soluble salts
Scale
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A type of intergranular attack corrosion that occurs at the grain boundaries under tensile stress
Stress corrosion cracking
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