Term
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Definition
| Process of adding electrons to or removing electrons from atoms or molecules, creating ions |
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Definition
| Measure of the ability of a substance to allow electron flow |
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Term
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Definition
| Deterioration of a material due to interaction with its environment. Electrochemical in nature because the corrosive chemical reactions involve transfer of charge. (Oxidation) |
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Definition
| Decomposition by electric current |
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Term
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Definition
| Process whereby the surface of a metal undergoes a slow, relatively uniform; removal of material. (Rust) |
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Term
| DESCRIBE an electrochemical cell with respect to the corrosion of metals |
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Definition
| Potential difference, or voltage, is established |
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Term
| STATE what happens to a metal during the oxidation step of the oxidation-reduction process |
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Definition
Metal Corrosion – oxidation of the overall oxidation-reduction process.
Oxidation – Process of Losing Electrons
Reduction – Process of Gaining Electrons |
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Term
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Definition
| Characteristic of a metal exhibited when that metal does not become active in the corrosion reaction. Caused by the buildup of a metal oxide layer which acts as a barrier. |
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Term
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Definition
| In electrochemical cells, the decrease in cell potential caused by the operation of the cell (current flow) is called polarization. |
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Term
| DESCRIBE the affects of passivity and polarization on the corrosion process |
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Definition
| Reduces/eliminates corrosion |
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Term
| LIST the two conditions that contribute to general corrosion. |
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Definition
Metal & water in the same environment.
Chemical reaction between two forming an oxide. |
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Term
| DESCRIBE how the rate of corrosion occurring in the plant is affected by Temperature |
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Definition
| Corrosion rates increase as temperature increase. |
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Term
| DESCRIBE how the rate of corrosion occurring in the plant is affected by Water Velocity |
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Definition
| High flow rate, 30 to 40 ft/sec, tends to remove the oxide film (exposing metal) allowing corrosion rate to increase. |
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Term
| DESCRIBE how the rate of corrosion occurring in the plant is affected by Oxygen |
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Definition
| Increases the corrosion rate due to the rapid reaction between the oxygen and polarizing layer of hydrogen absorbed on the oxide layer. |
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Term
| DESCRIBE how the rate of corrosion occurring in the plant is affected by pH |
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Definition
| A pH between 4 and 10 results in minimal corrosion rate. If the pH falls below or above this range, the corrosion will normally increase. |
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Term
| DESCRIBE how the rate of corrosion occurring in the plant is affected by Condition & Composition of the metal surface |
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Definition
| Deposits, scale, or irregular surfaces create areas on the metal where local corrosion can initiate and proceed at a faster rate than normal. Dissolved solids tend to make it easier for current to flow, which results in a higher corrosion rate. |
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Term
| LIST the three products that are formed from the general corrosion of iron. |
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Definition
FeO – First layer off the bare metal
Fe3O4 – Ferric Oxide – Second layer
Fe2O3 – Ferris Oxide – Final layer |
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Term
| STATE the four methods used to chemically control general plant corrosion. |
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Definition
1.) Pretreatment, or Passivation
2.) Add Chemical Substances – Passivators and Inhibitors
a. Example: Potassium Chromate Consist of a Naturally Active Metal That Corrodes at a Very Low Rate
3.) Cathodic Protection - External application of an external electric current to the iron so that it acts as a cathode and has no anodic areas.
b. Accomplished by using either an external electrical source or the use of a sacrificial anode to provide the electrical current (zinc).
4.) Water purity - Removing corrosive agents to reduce the dissolved oxygen and lesser extent carbon dioxide. Reduces the dissolved solids and conductivity. Chemical addition to alter the chemical reaction or tie up a particular corrodant. |
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Term
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Definition
| Corrosion 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. |
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Term
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Definition
| Corrosion byproduct deposited on the surfaces of the piping from the formation of insoluble compounds from normally soluble salts. (Most common-calcium or magnesium carbonates) |
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Term
| Define Galvanic Corrosion |
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Definition
| Results when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte |
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Term
| IDENTIFY the five problems associated with the presence or release of crud into reactor coolant. |
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Definition
1.) Fouling of Coolant Flow Paths
2.) Fouling of Heat Transfer Surfaces
3.) High General Background (Ambient) Radiation Levels
4.) Radiation Hot Spots
5.) Radioactive Waste Disposal |
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Term
| STATE the four causes of crud bursts. |
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Definition
1.) Increased oxygen concentration
2.) Reduced (or significantly changed) pH
3.) Large temperature change
4.) Physical shock (for example, starting and stopping pumps, changing speeds of pumps, reactor scram, or relief valve lift) |
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Term
| EXPLAIN the mechanism for galvanic corrosion. |
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Definition
| Electron flow through metals. Can be caused by two dissimilar metals with two different potentials or impure water. |
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Term
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Definition
| An accelerated localized attack requiring two conditions –low flow areas and high/low oxygen concentration. |
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Term
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Definition
| Pitting corrosion occurring specifically in low flow region. |
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Term
| Define Stress corrosion cracking |
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Definition
| Intergranular attack corrosion occurring at the grain boundaries under tensile stress. |
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Term
| STATE the two conditions necessary for pitting corrosion to occur. |
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Definition
1.) Low flow area.
2.) High or low oxygen concentration. |
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Term
| STATE the particular hazard associated with pitting corrosion. |
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Definition
| Hazard due to the possible rapid penetration of the metal with little overall loss of mass. |
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Term
| STATE the four controls used to minimize pitting corrosion. |
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Definition
1.) Avoiding stagnant conditions
2.) Using metals/alloys less susceptible to corrosion
3.) Avoiding agents that cause pitting
4.) Designing system/components with no crevices present |
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Term
| IDENTIFY the conditions necessary for intergranular stress corrosion cracking to occur. |
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Definition
1.) Alloy susceptible to stress corrosion cracking.
2.) Alloy exposed to specific environment.
3.) Alloy is in a stressed condition (Tensile stress) |
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Term
| STATE the hazard of intergranular stress corrosion cracking (IGSCC) |
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Definition
1.) Readily Crack Metal
Component or System Failure Causing:
a. Contamination
b. Loss of coolant
c. Loss of pressure |
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Term
| STATE the three controls used to prevent stress corrosion cracking. |
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Definition
1.) Maintain Low Chloride Ion Concentration
2.) Maintain Low Oxygen Content
3.) Use of Low Carbon Steels. |
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