06 Corrosion Problem Set

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CORROSION | PRACTICE PROBLEMS Complete the following to reinforce your understanding of the concept covered in this module.

PROBLEM 1: Wrought iron coated with magnesium is left to the elements. Over enough time what will happen? A. ๐‘‡โ„Ž๐‘’ ๐‘–๐‘Ÿ๐‘œ๐‘› ๐‘Ž๐‘›๐‘‘ ๐‘กโ„Ž๐‘’ ๐‘š๐‘Ž๐‘”๐‘›๐‘’๐‘ ๐‘–๐‘ข๐‘š ๐‘ค๐‘–๐‘™๐‘™ ๐‘“๐‘œ๐‘Ÿ๐‘š ๐‘Ž๐‘› ๐‘–๐‘Ÿ๐‘Ÿ๐‘’๐‘ฃ๐‘’๐‘Ÿ๐‘ ๐‘–๐‘๐‘™๐‘’ ๐‘โ„Ž๐‘’๐‘š๐‘–๐‘๐‘Ž๐‘™ ๐‘๐‘œ๐‘›๐‘‘ B. ๐‘€๐‘Ž๐‘”๐‘›๐‘’๐‘ ๐‘–๐‘ข๐‘š ๐‘ค๐‘–๐‘™๐‘™ ๐‘Ž๐‘๐‘ก ๐‘Ž๐‘  ๐‘Ž๐‘› ๐‘Ž๐‘›๐‘œ๐‘‘๐‘’ ๐‘Ž๐‘›๐‘‘ ๐‘๐‘œ๐‘Ÿ๐‘Ÿ๐‘œ๐‘‘๐‘’ C. ๐‘€๐‘Ž๐‘”๐‘›๐‘’๐‘ ๐‘–๐‘ข๐‘š ๐‘ค๐‘–๐‘™๐‘™ ๐‘Ž๐‘๐‘ก ๐‘Ž๐‘  ๐‘Ž ๐‘๐‘Ž๐‘กโ„Ž๐‘œ๐‘‘๐‘’ ๐‘Ž๐‘›๐‘‘ ๐‘๐‘œ๐‘Ÿ๐‘Ÿ๐‘œ๐‘‘๐‘’ D. ๐ผ๐‘Ÿ๐‘œ๐‘› ๐‘ค๐‘–๐‘™๐‘™ ๐‘Ž๐‘๐‘ก ๐‘Ž๐‘  ๐‘Ž๐‘› ๐‘Ž๐‘›๐‘œ๐‘‘๐‘’ ๐‘Ž๐‘›๐‘‘ ๐‘๐‘œ๐‘Ÿ๐‘Ÿ๐‘œ๐‘‘๐‘’

SOLUTION 1: The TOPIC OF CORROSION CONTROL is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. Therefore, we must memorize these concepts and understand their application independent of the NCEES Supplied Reference Handbook. Magnesium (๐‘€๐‘”) is anodic to steel (which is essentially iron, ๐น๐‘’). Thus, magnesium becomes the anode and corrodes and steel becomes the cathode and is protected. In this case, โ€œ๐‘€๐‘”โ€ is known as a SACRIFICIAL ANODE.

Therefore, the correct answer choice is B. Magnesium will act as anode and corrode.

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PROBLEM 2: In regards to corrosion, which of the following is NOT true? A. ๐‘‡โ„Ž๐‘’ ๐‘๐‘Ž๐‘กโ„Ž๐‘œ๐‘‘๐‘’ ๐‘™๐‘œ๐‘ ๐‘ ๐‘’๐‘  ๐‘š๐‘Ž๐‘ ๐‘  B. ๐‘‚๐‘ฅ๐‘–๐‘‘๐‘Ž๐‘ก๐‘–๐‘œ๐‘› ๐‘œ๐‘๐‘๐‘ข๐‘Ÿ๐‘  ๐‘Ž๐‘ก ๐‘กโ„Ž๐‘’ ๐‘Ž๐‘›๐‘œ๐‘‘๐‘’ C. ๐‘‡โ„Ž๐‘’ ๐‘Ž๐‘›๐‘œ๐‘‘๐‘’ ๐‘Ž๐‘›๐‘‘ ๐‘๐‘Ž๐‘กโ„Ž๐‘œ๐‘‘๐‘’ ๐‘š๐‘ข๐‘ ๐‘ก ๐‘๐‘’ ๐‘’๐‘™๐‘’๐‘๐‘ก๐‘Ÿ๐‘–๐‘๐‘Ž๐‘™๐‘™๐‘ฆ ๐‘๐‘œ๐‘›๐‘›๐‘’๐‘๐‘ก๐‘’๐‘‘ D. ๐‘Š๐‘Ž๐‘ก๐‘’๐‘Ÿ ๐‘ข๐‘ ๐‘ข๐‘Ž๐‘™๐‘™๐‘ฆ ๐‘๐‘™๐‘Ž๐‘ฆ๐‘  ๐‘Ž๐‘› ๐‘–๐‘š๐‘๐‘œ๐‘Ÿ๐‘ก๐‘Ž๐‘›๐‘ก ๐‘Ÿ๐‘œ๐‘™๐‘’

SOLUTION 2: The EQUATIONS FOR POSSIBLE CATHODE REACTIONS (REDUCTION) OF A TYPICAL METAL can be referenced under the topic of CORROSION on page 60 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. REDUCTION is the process by which metals conserve electrons. In the chemical reaction below, electrons are consumed: ๐‘€>? + ๐‘› โ†’ ๐‘€ A reduction occurring at the cathode is characterized by the plating of metal ions that form the electrolyte or the generation of hydrogen gas from dissolved hydrogen ions in the electrolyte.

Therefore, the correct answer choice is A. ๐‘ป๐’‰๐’† ๐’„๐’‚๐’•๐’‰๐’๐’…๐’† ๐’๐’๐’”๐’†๐’” ๐’Ž๐’‚๐’”๐’”



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PROBLEM 3: A copper hook is attached to a plain carbon steel chain below the surface in a saltwater bay. If galvanic corrosion occurs, what will be the anodic reaction? A. ๐ถ๐‘ขN? + 2๐‘’ P โ†’ ๐ถ๐‘ข B. ๐ถ๐‘ข โ†’ ๐ถ๐‘ขN? + 2๐‘’ P C. ๐น๐‘’ โ†’ ๐น๐‘’ N? + 2๐‘’ P D. ๐‘๐‘Ž๐ถ๐‘™ โ†’ ๐‘๐‘Ž? + ๐ถ๐‘™ P

SOLUTION 3: The TABLE LISTING THE STANDARD ELECTROMOTIVE POTENTIALS OF METALS can be referenced under the topic of ELECTROCHEMISTRY on page 59 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. Using the table of standard electromotive potentials of metals, we can determine the behavior of dissimilar metals in salt water. Iron is anodic with respect to copper. Therefore, the anodic oxidation half-cell reaction for iron will occur.

Therefore, the correct answer choice is C. ๐‘ญ๐’† โ†’ ๐‘ญ๐’†๐Ÿ? + ๐Ÿ๐’†P



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PROBLEM 4: All but which of the following statements about the rusting of iron are correct? A. ๐ถ๐‘œ๐‘›๐‘ก๐‘Ž๐‘๐‘ก ๐‘ค๐‘–๐‘กโ„Ž ๐‘ค๐‘Ž๐‘ก๐‘’๐‘Ÿ ๐‘œ๐‘Ÿ ๐‘œ๐‘ฅ๐‘ฆ๐‘”๐‘’๐‘› ๐‘–๐‘  ๐‘Ÿ๐‘’๐‘ž๐‘ข๐‘–๐‘Ÿ๐‘’๐‘‘ ๐‘“๐‘œ๐‘Ÿ ๐‘Ÿ๐‘ข๐‘ ๐‘ก๐‘–๐‘›๐‘” ๐‘ก๐‘œ ๐‘œ๐‘๐‘๐‘ข๐‘Ÿ B. ๐ป๐‘Ž๐‘™๐‘–๐‘‘๐‘’๐‘  ๐‘Ž๐‘”๐‘”๐‘Ÿ๐‘Ž๐‘ฃ๐‘Ž๐‘ก๐‘’ ๐‘Ÿ๐‘ข๐‘ ๐‘ก๐‘–๐‘›๐‘”, ๐‘Ž ๐‘๐‘Ÿ๐‘œ๐‘๐‘’๐‘ ๐‘  ๐‘คโ„Ž๐‘–๐‘โ„Ž ๐‘–๐‘›๐‘ฃ๐‘œ๐‘™๐‘ฃ๐‘’๐‘  ๐‘’๐‘™๐‘๐‘ก๐‘Ÿ๐‘œ๐‘โ„Ž๐‘’๐‘š๐‘–๐‘๐‘Ž๐‘™๐‘  ๐‘œ๐‘ฅ๐‘–๐‘‘๐‘Ž๐‘ก๐‘–๐‘œ๐‘› โˆ’ ๐‘Ÿ๐‘’๐‘‘๐‘ข๐‘๐‘ก๐‘–๐‘œ๐‘› ๐‘Ÿ๐‘’๐‘Ž๐‘๐‘ก๐‘–๐‘œ๐‘›๐‘  C. ๐ถ๐‘œ๐‘›๐‘ก๐‘Ž๐‘๐‘ก ๐‘ค๐‘–๐‘กโ„Ž ๐‘Ž ๐‘š๐‘œ๐‘Ÿ๐‘’ ๐‘’๐‘™๐‘๐‘ก๐‘Ÿ๐‘œ๐‘๐‘œ๐‘ ๐‘–๐‘ก๐‘–๐‘ฃ๐‘’ ๐‘š๐‘’๐‘ก๐‘Ž๐‘™ ๐‘Ÿ๐‘’๐‘ ๐‘ก๐‘Ÿ๐‘–๐‘๐‘ก๐‘  ๐‘Ÿ๐‘ข๐‘ ๐‘ก๐‘–๐‘›๐‘” D. ๐ถ๐‘œ๐‘Ÿ๐‘Ÿ๐‘œ๐‘ ๐‘–๐‘œ๐‘› ๐‘œ๐‘๐‘๐‘ข๐‘Ÿ๐‘  ๐‘–๐‘› ๐‘œ๐‘ฅ๐‘ฆ๐‘”๐‘’๐‘› โˆ’ ๐‘Ÿ๐‘–๐‘โ„Ž ๐‘Ž๐‘Ÿ๐‘’๐‘Ž๐‘ 

SOLUTION 4: The TOPIC OF RUSTING is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. Therefore, we must memorize these concepts and understand their application independent of the NCEES Supplied Reference Handbook. Since oxygen is required for rust formation, oxygen-depleted areas become the anode and are corroded. This may lead to pitting, particularly if rust or other corrosion products are accumulated locally to prevent the access of oxygen. Iron and other metals may be protected from corrosion by the presence of a more electropositive metal such as magnesium or zinc. This is the reason for coating steel with zinc to produce galvanized sheet.

Therefore, the correct answer choice is D. ๐‘ช๐’๐’“๐’“๐’๐’”๐’Š๐’๐’ ๐’๐’„๐’„๐’–๐’“๐’” ๐’Š๐’ ๐’๐’™๐’š๐’ˆ๐’†๐’ โˆ’ ๐’“๐’Š๐’„๐’‰ ๐’‚๐’“๐’†๐’‚๐’”.



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PROBLEM 5: Why is aluminum more rust-resistance than steel? A. ๐‘‡โ„Ž๐‘’ ๐‘Ÿ๐‘’๐‘Ž๐‘๐‘ก๐‘–๐‘œ๐‘› ๐‘Ÿ๐‘Ž๐‘ก๐‘’ ๐‘ค๐‘–๐‘กโ„Ž ๐‘Ž๐‘ก๐‘š๐‘œ๐‘ ๐‘โ„Ž๐‘’๐‘Ÿ๐‘–๐‘ ๐‘œ๐‘ฅ๐‘ฆ๐‘”๐‘’๐‘› ๐‘–๐‘  โ„Ž๐‘–๐‘”โ„Ž๐‘’๐‘Ÿ ๐‘“๐‘œ๐‘Ÿ ๐‘ ๐‘ก๐‘’๐‘’๐‘™ B. ๐‘‡โ„Ž๐‘’ ๐‘Ÿ๐‘’๐‘Ž๐‘๐‘ก๐‘–๐‘œ๐‘› ๐‘Ÿ๐‘Ž๐‘ก๐‘’ ๐‘ค๐‘–๐‘กโ„Ž ๐‘Ž๐‘ก๐‘š๐‘œ๐‘ ๐‘โ„Ž๐‘’๐‘Ÿ๐‘–๐‘ ๐‘œ๐‘ฅ๐‘ฆ๐‘”๐‘’๐‘› ๐‘–๐‘  โ„Ž๐‘–๐‘”โ„Ž๐‘’๐‘Ÿ ๐‘“๐‘œ๐‘Ÿ ๐‘Ž๐‘™๐‘ข๐‘š๐‘–๐‘›๐‘ข๐‘š C. ๐ผ๐‘Ÿ๐‘œ๐‘› ๐‘Ž๐‘ก๐‘œ๐‘š๐‘  ๐‘Ž๐‘Ÿ๐‘’ ๐‘™๐‘Ž๐‘Ÿ๐‘”๐‘’๐‘Ÿ ๐‘กโ„Ž๐‘Ž๐‘› ๐‘Ž๐‘™๐‘ข๐‘š๐‘–๐‘›๐‘ข๐‘š ๐‘Ž๐‘ก๐‘œ๐‘š๐‘ , ๐‘Ž๐‘›๐‘‘ ๐‘กโ„Ž๐‘ข๐‘ , ๐‘กโ„Ž๐‘’ ๐‘–๐‘›๐‘ก๐‘’๐‘Ÿ๐‘ ๐‘ก๐‘–๐‘ก๐‘–๐‘Ž๐‘™ ๐‘ ๐‘๐‘Ž๐‘๐‘’๐‘  ๐‘Ž๐‘Ÿ๐‘’ ๐‘™๐‘Ž๐‘Ÿ๐‘”๐‘’๐‘Ÿ D. ๐ผ๐‘Ÿ๐‘œ๐‘› โ„Ž๐‘Ž๐‘  ๐‘”๐‘Ÿ๐‘’๐‘Ž๐‘ก๐‘’๐‘Ÿ ๐‘š๐‘Ž๐‘”๐‘›๐‘’๐‘ก๐‘–๐‘ ๐‘๐‘Ÿ๐‘œ๐‘๐‘’๐‘Ÿ๐‘ก๐‘–๐‘’๐‘  ๐‘กโ„Ž๐‘Ž๐‘› ๐‘Ž๐‘™๐‘ข๐‘š๐‘–๐‘›๐‘ข๐‘š

SOLUTION 5: The TOPIC OF CORROSION CONTROL is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. Therefore, we must memorize these concepts and understand their application independent of the NCEES Supplied Reference Handbook. Aluminum (๐ด๐‘™) has a higher oxidation potential than Iron (๐น๐‘’). Yet, aluminum has better corrosion resistance than iron. This is because aluminum reacts readily with oxygen to form a stable coating of aluminum oxide, which protects the base metal. This phenomenon is known as PASSIVITY and also accounts for the excellent corrosion resistance of stainless steel due to the presence of chromium oxide protective film.

Therefore, the correct answer choice is B. The reaction rate with atmospheric oxygen is higher for aluminum.



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PROBLEM 6: What is the electrical potential of the chemical reactions of potassium gaining an electron? A. โˆ’0.788 B. โˆ’0.337 C. +2.363 D. +2.925

SOLUTION 6: The PERIODIC TABLE OF ELEMENTS can be referenced under the topic of CHEMISTRY on page 55 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The first thing we must do in this problem is identify the atomic symbol used to represent the element of potassium. Looking at the periodic table, we know that potassium is represented by the symbol โ€œ๐พโ€. The TABLE LISTING THE STANDARD ELECTROMOTIVE POTENTIALS OF METALS can be referenced under the topic of ELECTROCHEMISTRY on page 59 of the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. The next step in this problem is to look at the table in reference handbook that lists out the standard oxidation potential for corrosion reactions, and the associated electrical potential for each reaction.



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In the problem statement we are asked for the electrical potential of a chemical reaction when potassium gains an electron. We realize that the chemical reaction must use the symbol โ€œ๐พโ€ to represent potassium, as well as have the addition or subtraction of electrons, represented by the symbol ๐‘’ P . Looking at the table in the reference handbook, we find the chemical reaction for potassium gaining an electron listed as: ๐พ โ†’ ๐พ? + ๐‘’P



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Looking at the associated electrical potential for this reaction, we find the electrical potential of potassium gaining an electron is +2.925 Volts.

Therefore, the correct answer choice is D. +๐Ÿ. ๐Ÿ—๐Ÿ๐Ÿ“ PROBLEM 7: If you were to design a transmission line steel structure and place it in a humid environment, you would need to be wary of corrosion control due to the environmental constrains. Which of the following answer choices would help prevent rusting of the structure? A. ๐‘ˆ๐‘ ๐‘–๐‘›๐‘” ๐‘๐‘œ๐‘™๐‘ก๐‘  ๐‘“๐‘œ๐‘Ÿ ๐‘ ๐‘ก๐‘Ÿ๐‘ข๐‘๐‘ก๐‘ข๐‘Ÿ๐‘Ž๐‘™ ๐‘๐‘œ๐‘›๐‘›๐‘’๐‘๐‘ก๐‘–๐‘œ๐‘›๐‘  B. ๐บ๐‘Ž๐‘™๐‘ฃ๐‘Ž๐‘›๐‘–๐‘ง๐‘’ ๐‘กโ„Ž๐‘’ ๐‘ ๐‘ก๐‘Ÿ๐‘ข๐‘๐‘ก๐‘ข๐‘Ÿ๐‘’ ๐‘ค๐‘–๐‘กโ„Ž ๐‘Ž ๐‘ง๐‘–๐‘›๐‘ ๐‘๐‘œ๐‘Ž๐‘ก๐‘–๐‘›๐‘” C. ๐ด๐‘™๐‘™๐‘œ๐‘ค ๐‘กโ„Ž๐‘’ ๐‘ ๐‘ก๐‘Ÿ๐‘ข๐‘๐‘ก๐‘ข๐‘Ÿ๐‘’ ๐‘ก๐‘œ ๐‘๐‘’ ๐‘’๐‘ฅ๐‘๐‘œ๐‘ ๐‘’๐‘‘ ๐‘ก๐‘œ ๐‘กโ„Ž๐‘’ ๐‘’๐‘›๐‘ฃ๐‘–๐‘Ÿ๐‘œ๐‘›๐‘š๐‘’๐‘›๐‘ก D. ๐‘๐‘œ๐‘›๐‘’ ๐‘œ๐‘“ ๐‘กโ„Ž๐‘’ ๐‘Ž๐‘๐‘œ๐‘ฃ๐‘’

SOLUTION 7: The TOPIC OF CORROSION CONTROL is not provided in the NCEES Supplied Reference Handbook, Version 9.4 for Computer Based Testing. Therefore, we must memorize these concepts and understand their application independent of the NCEES Supplied Reference Handbook.



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Structural steel is commonly galvanized with zinc to prevent rusting. If the Zinc coating is punctured, the steel becomes the cathode and is protected. On the other hand, if a tin coating on steel is punctured, the steel underneath corrodes very rapidly because it is anodic to tin.

Therefore, the correct answer choice is B. ๐‘ฎ๐’‚๐’๐’—๐’‚๐’๐’Š๐’›๐’† ๐’•๐’‰๐’† ๐’”๐’•๐’“๐’–๐’„๐’•๐’–๐’“๐’† ๐’˜๐’Š๐’•๐’‰ ๐’‚ ๐’›๐’Š๐’๐’„ ๐’„๐’๐’‚๐’•๐’Š๐’๐’ˆ



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