This set of Corrosion Engineering MCQs focuses on “Eight Forms – Cavitation and Fretting Corrosion”.
1. Which of the following type of corrosion is caused by the formation and collapse of vapor bubbles in a liquid near the metal surface?
a) Filiform corrosion
b) Fretting corrosion
c) Cavitation damage
d) Crevice corrosion
View Answer
Explanation: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface.
2. Which of the following equipment encounters cavitation damage in the service?
a) Hydraulic turbines
b) Ship propellers
c) Pump impellers
d) Hydraulic turbines, ship propellers, and pump impellers
View Answer
Explanation: Cavitation damage occurs in hydraulic turbines, ship propellers, pump impellers, and other surfaces where high-velocity liquid flow and pressure changes are encountered.
3. Which of the following condition is/are correct regarding the boiling point of a liquid with an increase in pressure?
a) Decreases up to triple point
b) Increases up to triple point
c) Increases up to the critical point
d) Decreases up to the critical point
View Answer
Explanation: As the pressure of a liquid decreases, its boiling point decreases up to its triple point. As the pressure increases its increases up to a critical point.
Example: At higher altitudes boiling point of liquids reaches low as atmospheric pressure decreased.
4. Which of the following will result due to cavitation damage of a metal?
a) Mechanical action
b) Chemical dissolution
c) Both mechanical action and chemical dissolution
d) Neither mechanical action nor chemical dissolution
View Answer
Explanation: Cavitation damage is the special form of erosion-corrosion that occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. It results in the mechanical and chemical dissolution of metal.
5. Cavitation damaged can be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow.
a) False
b) True
View Answer
Explanation: Cavitation damaged can indeed be reduced by changing the design to minimize hydrodynamic pressure differences in process streamflow. It reduces the impingement area and force of the stream.
6. Which of the following type of corrosion is depicted in the given figure?
a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
View Answer
Explanation: Cavitation damage is depicted in the given figure. It occurs by the formation and collapse of vapor bubbles in a liquid near a metal surface. And it results in mechanical action and chemical dissolution of metal.
7. Which of the following type of corrosion that occurs at contact areas between materials under load subjected to vibration or relative motion?
a) Fretting corrosion
b) Crevice corrosion
c) Cavitation damage
d) Pitting corrosion
View Answer
Explanation: Fretting corrosion is the special type of erosion-corrosion that occurs at the contact areas between materials under load subjected to vibration or relative motion.
8. Which of the following is/are the other names of fretting corrosion?
a) Friction oxidation
b) Wear oxidation
c) False brinelling
d) Friction oxidation, wear oxidation and false brinelling
View Answer
Explanation: Fretting corrosion is one of the special types of erosion-corrosion. It also called friction oxidation, wear oxidation, chafing, and false brinelling. Because it gets initiated with wear or friction and oxides debris are formed during corrosion.
9. Which of the following is/are the classic cases of fretting corrosion?
a) Bolted tie plates on railroad rails
b) Press-fitted ball bearing race on a shaft
c) On ball bearings
d) Bolted tie plates on railroad rails and press-fitted ball bearing race on a shaft
View Answer
Explanation: Fretting corrosion occurs at contact areas between materials under load subjected to vibration or repeated relative motion. And it doesn’t occur on materials in continuous motion such as on ball bearings.
10. Which of the following is/are the basic requirements for the occurrence of fretting corrosion?
a) The interface must be under load
b) Vibration or repeated relative motion between the two surfaces
c) The interface must be under load and vibration or repeated relative motion between the two surfaces
d) The relative motion should be high
View Answer
Explanation: The basic requirements for the occurrence of fretting corrosion are:
i. The interface must be under load
ii. Vibration or repeated relative motion between the two surfaces
iii. The load and the relative motion of the interface must be sufficient to produce deformation.
11. Which of the following is/are the preventive measures of fretting corrosion?
a) Lubricate with low-viscosity, high-tenacity oil
b) Increasing surface hardness by shot-peening or cold working
c) Use gaskets to absorb vibrations
d) Lubricate with low-viscosity, high-tenacity oil, increasing surface hardness by shot-peening and use gaskets to absorb vibrations
View Answer
Explanation: Preventive measures to minimize fretting corrosion:
i. Lubricate with low-viscosity, high-tenacity oil, and greases
ii. Increasing surface hardness by shot-peening or cold working
iii. Use gaskets to absorb vibrations and exclude oxygen at bearing surfaces
iv. Increase the load to decrease slip between two metals.
Sanfoundry Global Education & Learning Series – Corrosion Engineering.
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