# Corrosion Engineering Questions and Answers – Testing – Exposure Techniques and its Factors – 2

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This set of Corrosion Engineering Multiple Choice Questions & Answers focuses on “Testing – Exposure Techniques and its Factors – 2”.

1. The Corrodibility of the metal in a corrosion test may decrease or increase as a function of time.
a) True
b) False

Explanation: Corrodibility of the metal is defined as the capability of being corroded. It may decrease or increase during the corrosion test as a function of time. It increases as it owing to the formation of a protective layer or it decreases as it owing removal of the more resistant surface layer.

2. Which of the following is/are the factors that affect corrosion testing?
a) Temperature
b) Dissolved oxygen
c) Nature of metal
d) Temperature, dissolved oxygen, and nature of metal

Explanation: The factors that affect corrosion testing are:
i. Temperature
ii. Dissolved oxygen
iii. Nature of metal
iv. The concentration of the corrosive solution
v. Specifications of the specimen (Fabrication history, metallurgical history).

3. Which of the following metals in which corrosion decreases with an increase in temperature in oxygenated corrosive solutions?
a) Copper and its alloys
b) Steels
c) Cast irons
d) Aluminum and its alloys

Explanation: Temperature is one of the important factors of corrosion. In many cases, an increase in temperature increases the corrosion rate of metals. Whereas it decreases in copper alloys due to the removal of dissolved oxygen.
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4. Which of the following standard expression is used to measure the corrosion rate of a metal?
a) Mils per year = W/DAT
b) Mils per year = 534W/DAT
c) Milligrams decimeter per day = 534W/DAT
d) Milligrams decimeter per day = W/DAT

Explanation: Standard expression to measure the corrosion rate in mils per year = 534W/DAT.
Where D is the density of metal, W is weight loss in milligrams, A is the area of exposure in sq. inches, T is time in hours.

5. Which of the following units are used in terms of penetration of pits on a metal?
a) Milligram sq. decimeter per day (MDD)
b) Mils per year (MPY)
c) Both MDD and MPY
d) Neither MDD nor MPY

Explanation: Mils per year is commonly used corrosion rate expression as it measures corrosion rate in terms of depth of penetration of pit. Whereas milligram sq. decimeter per day (MDD) measures the corrosion rate in terms of weight loss of metal.

6. Which of the following expression is used for electrochemical techniques to determine the corrosion penetration rate?
a) Corrosion penetration rate = K (ai/D)
b) Corrosion penetration rate = K (ai/nD)
c) Corrosion penetration rate = (ai/nD)
d) Corrosion penetration rate = (ai/nD)

Explanation: The corrosion rate expression that is used for electrochemical techniques to determine corrosion penetration rate is K (ai/nD) where a is the atomic weight of the metal, i is current density (in microamperes per sq. centimeters), n is the number of electrons lost, D is the density of metal, K is constant depends on the penetration rate desired.

7. Calculate the corrosion penetration rate of iron that corroding at an electrochemical corrosion rate of 1 microampere/sq. centimeters?
a) 0.212 mpy
b) 0.11 mpy
c) 0.46 mpy
d) 0.64 mpy

Explanation: Corrosion penetration rate = K (ai/nD)
a = atomic weight of iron = 55.8 g
i = current density = 1 micrometer/sq. Centimeters
n = valency change = 2
D = density of iron = 7.86 g/cm3
K = 0.129 for steel
Corrosion penetration rate = 0.129 * [(55.8) / (2*7.86)] = 0.46 mpy.

8. Which of the following is/are the corrosion testing’s for stainless steels?
a) Warren test
b) Streicher test
c) Huey test
d) Warren test, Streicher test and huey test

Explanation: Warren test, Streicher test and huey test are the corrosion testing’s for stainless steel. The primary function of these testing’s is to find out the sensitized stainless-steel metal specimens.

9. Which of the following method is the best approach to report the results of the pitting corrosion test?
a) Reporting the number of pits per unit area
b) Reporting maximum depth of a pit
c) Reporting average depth of pits
d) Reporting weight loss of a metal

Explanation: Pitting corrosion is one of the types of corrosion in which perforated metal is formed due to the formation of holes on the metal surface. The best way to report the corrosion testing of pitting is to report the maximum depth of a pit.

10. Which of the following factors are considered to evaluate the paint test?
a) Appearance of coating
b) Presence and extent of corrosion
c) Under film corrosion
d) The appearance of coating, presence, and extent of corrosion and under film corrosion

Explanation: The factors that are considered to evaluate the paint test are:
i. Appearance of coating
ii. Presence and extent of corrosion
iii. Under film corrosion.

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