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Questions and Answers

EASY What is a necessary condition for galvanic corrosion to occur?

When two identical metals contact each other

When two dissimilar metals contact each other and are surrounded by an electrolyte (correct)

When a metal is exposed to water

When a metal is exposed to air

What happens to the anodic metal in a galvanic corrosion process?

It loses electrons and soluble metal ions are left behind (correct)

It gains electrons and becomes more noble

It remains unchanged

It becomes more reactive

What is the role of the electrolyte in galvanic corrosion?

To provide an electric field

To accelerate the corrosion process

To provide a pathway for electrons to flow (correct)

To separate the two metals

What determines the rate of corrosion in galvanic corrosion?

The potential difference between the two metals Signup and view all the answers

What is the electromotive series?

A list of metals in order of their electrochemical potential Signup and view all the answers

What happens when a metal is under stress, such as in a bend or dent?

It becomes more anodic Signup and view all the answers

Why do noble metals not readily corrode?

Because they have a high electrochemical potential Signup and view all the answers

What is stress corrosion cracking?

A type of corrosion that occurs in areas under stress, such as bends or dents Signup and view all the answers

Which metal has the highest electrochemical potential?

Gold Signup and view all the answers

What is the purpose of a sacrificial anode?

To protect other metals from corrosion Signup and view all the answers

What is the electrochemical potential of hydrogen?

0.00 V Signup and view all the answers

What is the result of the reaction at the cathode in a zinc-copper galvanic cell?

Formation of H2 gas Signup and view all the answers

What is the rule of thumb for the electrochemical potential difference between two materials to minimize galvanic corrosion?

Less than 0.15 V Signup and view all the answers

What is the purpose of monitoring closed loop corrosion?

To identify areas of high corrosion Signup and view all the answers

What is the purpose of corrosion coupons?

To monitor corrosion rates Signup and view all the answers

What is the result of the reaction at the anode in a zinc-copper galvanic cell?

Formation of Zn2+ cations Signup and view all the answers

What is the purpose of using borescopes in closed system corrosion monitoring?

To inspect the inside of tubes and shells for signs of corrosion Signup and view all the answers

MEDIUM What is the purpose of checking pressure drops and flow rates across heat exchangers and strainers?

To identify corrosion or deposition Signup and view all the answers

What is the reason for galvanic corrosion occurrence even when there is only one type of metal present?

All of the above Signup and view all the answers

What happens to the anodic metal in a galvanic corrosion process when it loses electrons?

Soluble metal ions are left behind Signup and view all the answers

What determines the direction of electron flow between two metals in a galvanic cell?

Electrochemical potential difference Signup and view all the answers

What is the purpose of the electromotive series?

To show the voltage difference between metals in a galvanic cell Signup and view all the answers

What happens in stress corrosion cracking?

The area under stress becomes more anodic Signup and view all the answers

Why do noble metals not readily corrode?

Because they receive electrons from anodic metals Signup and view all the answers

What is the correlation between the electrochemical potential difference and the rate of corrosion?

The greater the potential difference, the faster the rate of corrosion Signup and view all the answers

What is the role of the electrolyte in galvanic corrosion?

To provide a pathway for ions to move Signup and view all the answers

In a galvanic corrosion process, which of the following ions are involved in the reaction at the cathode?

H+ and OH- Signup and view all the answers

What is the primary reason for using sacrificial anodes in a galvanic corrosion process?

To reduce the corrosion rate of the cathode Signup and view all the answers

Which of the following metals would be the most effective sacrificial anode in a galvanic corrosion process?

Lithium Signup and view all the answers

What is the purpose of monitoring pH in closed system corrosion monitoring?

To adjust the corrosion inhibitor residual in the system Signup and view all the answers

What is the result of the reaction at the anode in a zinc-copper galvanic cell?

Formation of zinc hydroxide Signup and view all the answers

Which of the following is a common method for preventing galvanic corrosion in industrial applications?

Electrically insulating dissimilar metals Signup and view all the answers

What is the purpose of checking pipes and piping connections for leaks in closed system corrosion monitoring?

To identify areas where corrosion is most likely to occur Signup and view all the answers

What is the role of oxygen scavengers in closed system corrosion monitoring?

To remove oxygen from the system to prevent corrosion Signup and view all the answers

Which of the following is a common method for monitoring corrosion in closed systems?

Using corrosion coupons Signup and view all the answers

What is the primary reason for replacing dissimilar piping with piping of similar materials in closed system corrosion monitoring?

To prevent galvanic corrosion Signup and view all the answers

HARD What is the primary reason why a pipe made of a single material can still undergo galvanic corrosion?

Surface imperfections and crystal misalignment create differences in electrochemical potential Signup and view all the answers

What happens to the anodic metal when it loses electrons in a galvanic corrosion process?

Soluble metal ions are left behind and enter the electrolyte Signup and view all the answers

What is the primary reason why zinc is often used as a sacrificial anode in galvanic corrosion prevention?

Because it has a low electrochemical potential Signup and view all the answers

What is the role of conductivity testing in closed system corrosion monitoring?

To detect corrosion potential Signup and view all the answers

What is the primary reason why noble metals do not readily corrode?

They have a low electrochemical potential and are less reactive Signup and view all the answers

What is the correlation between the electrochemical potential difference and the rate of corrosion in galvanic corrosion?

The greater the electrochemical potential difference, the faster the rate of corrosion Signup and view all the answers

What is the purpose of using borescopes in closed system corrosion monitoring?

To inspect the inside of tubes and shells for signs of corrosion or deposition Signup and view all the answers

What is the correlation between the electrochemical potential difference and the rate of corrosion?

A higher electrochemical potential difference results in faster corrosion Signup and view all the answers

What is the primary reason why a metal under stress, such as in a bend or dent, is more susceptible to corrosion?

The metal is more anodic and has a higher electrochemical potential difference with the surrounding metal Signup and view all the answers

What is the primary purpose of the electromotive series?

To compare the electrochemical potential of different metals Signup and view all the answers

Why is it important to replace dissimilar piping with piping of similar materials in closed system corrosion monitoring?

To prevent galvanic corrosion Signup and view all the answers

What is the purpose of monitoring oxygen scavenger residuals in closed system corrosion monitoring?

To prevent oxygen-related corrosion Signup and view all the answers

What is the role of the electrolyte in galvanic corrosion?

To provide a pathway for ions to move between the anode and cathode Signup and view all the answers

What is the primary reason why a scratch or dent can cause galvanic corrosion in a metal?

The scratch or dent creates a area of low electrochemical potential Signup and view all the answers

What is the primary reason for using corrosion coupons in closed system corrosion monitoring?

To monitor corrosion rates Signup and view all the answers

What is the role of corrosion inhibitors in closed system corrosion monitoring?

To reduce the corrosion rate Signup and view all the answers

What is the purpose of checking pipes and piping connections for leaks in closed system corrosion monitoring?

To detect potential corrosion sites Signup and view all the answers

What is the result of the reaction at the cathode in a zinc-copper galvanic cell?

The release of hydrogen gas Signup and view all the answers

Study Notes

Galvanic Corrosion

Occurs when two dissimilar metals contact each other in an electrolyte (an aqueous solution)
Each metal has a characteristic electrochemical potential, causing electrons to flow from the more negative metal (anode) to the more positive metal (cathode)

Anode and Cathode

Anode loses electrons, leaving behind soluble metal ions that enter solution with the electrolyte, causing corrosion
Cathode receives electrons, resulting in a build-up of hydrogen gas

Electrochemical Potential

The difference in electrochemical potential between two metals causes galvanic corrosion
Electrochemical potential is listed in the electromotive series (Table 2)
Metals at the top of the table are the most cathodic (noble) and do not readily corrode

Galvanic Cell

A galvanic cell consists of two metals with different electrochemical potentials, surrounded by an electrolyte
The greater the potential difference between the two metals, the greater the rate of corrosion

Corrosion Process

Electrons flow from the anode to the cathode, creating ions that enter solution with the electrolyte
At the cathode, electrons combine with hydrogen ions to form hydrogen gas
At the anode, metal ions combine with hydroxide ions to form a precipitate

Preventing Galvanic Corrosion

Use materials with similar electrochemical potentials
Electrically insulate dissimilar metals
Use sacrificial anodes to protect more noble metals
Regularly replace sacrificial anodes

Monitoring Closed Loop Corrosion

Use instruments to monitor corrosion or system corrosiveness
Perform visual inspections and checks to determine active corrosion sites
Remove and examine corrosion coupons on a regular basis
Inspect the integrity of sacrificial anodes
Perform tests on closed system water to determine pH, oxygen scavenger residual, conductivity, and corrosion inhibitor residual

Preventing Closed System Corrosion

Replace dissimilar piping with piping of similar materials
Install special dielectric pipe fittings if piping connections between dissimilar metals are unavoidable
Install sacrificial anodes and replace them regularly
Add corrosion inhibitor and oxygen scavenger according to plant water treatment recommendations

Galvanic Corrosion

Occurs when two dissimilar metals contact each other in an electrolyte (an aqueous solution)
Each metal has a characteristic electrochemical potential, causing electrons to flow from the more negative metal (anode) to the more positive metal (cathode)

Anode and Cathode

Anode loses electrons, leaving behind soluble metal ions that enter solution with the electrolyte, causing corrosion
Cathode receives electrons, resulting in a build-up of hydrogen gas

Electrochemical Potential

The difference in electrochemical potential between two metals causes galvanic corrosion
Electrochemical potential is listed in the electromotive series (Table 2)
Metals at the top of the table are the most cathodic (noble) and do not readily corrode

Galvanic Cell

A galvanic cell consists of two metals with different electrochemical potentials, surrounded by an electrolyte
The greater the potential difference between the two metals, the greater the rate of corrosion

Corrosion Process

Electrons flow from the anode to the cathode, creating ions that enter solution with the electrolyte
At the cathode, electrons combine with hydrogen ions to form hydrogen gas
At the anode, metal ions combine with hydroxide ions to form a precipitate

Preventing Galvanic Corrosion

Use materials with similar electrochemical potentials
Electrically insulate dissimilar metals
Use sacrificial anodes to protect more noble metals
Regularly replace sacrificial anodes

Monitoring Closed Loop Corrosion

Use instruments to monitor corrosion or system corrosiveness
Perform visual inspections and checks to determine active corrosion sites
Remove and examine corrosion coupons on a regular basis
Inspect the integrity of sacrificial anodes
Perform tests on closed system water to determine pH, oxygen scavenger residual, conductivity, and corrosion inhibitor residual

Preventing Closed System Corrosion

Replace dissimilar piping with piping of similar materials
Install special dielectric pipe fittings if piping connections between dissimilar metals are unavoidable
Install sacrificial anodes and replace them regularly
Add corrosion inhibitor and oxygen scavenger according to plant water treatment recommendations

Galvanic Corrosion

Occurs when two dissimilar metals contact each other in an electrolyte (an aqueous solution)
Each metal has a characteristic electrochemical potential, causing electrons to flow from the more negative metal (anode) to the more positive metal (cathode)

Anode and Cathode

Anode loses electrons, leaving behind soluble metal ions that enter solution with the electrolyte, causing corrosion
Cathode receives electrons, resulting in a build-up of hydrogen gas

Electrochemical Potential

The difference in electrochemical potential between two metals causes galvanic corrosion
Electrochemical potential is listed in the electromotive series (Table 2)
Metals at the top of the table are the most cathodic (noble) and do not readily corrode

Galvanic Cell

A galvanic cell consists of two metals with different electrochemical potentials, surrounded by an electrolyte
The greater the potential difference between the two metals, the greater the rate of corrosion

Corrosion Process

Electrons flow from the anode to the cathode, creating ions that enter solution with the electrolyte
At the cathode, electrons combine with hydrogen ions to form hydrogen gas
At the anode, metal ions combine with hydroxide ions to form a precipitate

Preventing Galvanic Corrosion

Use materials with similar electrochemical potentials
Electrically insulate dissimilar metals
Use sacrificial anodes to protect more noble metals
Regularly replace sacrificial anodes

Monitoring Closed Loop Corrosion

Use instruments to monitor corrosion or system corrosiveness
Perform visual inspections and checks to determine active corrosion sites
Remove and examine corrosion coupons on a regular basis
Inspect the integrity of sacrificial anodes
Perform tests on closed system water to determine pH, oxygen scavenger residual, conductivity, and corrosion inhibitor residual

Preventing Closed System Corrosion

Replace dissimilar piping with piping of similar materials
Install special dielectric pipe fittings if piping connections between dissimilar metals are unavoidable
Install sacrificial anodes and replace them regularly
Add corrosion inhibitor and oxygen scavenger according to plant water treatment recommendations

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Description

Learn about the process of galvanic corrosion, where two dissimilar metals in contact with an electrolyte cause electrons to flow, resulting in corrosion.