AMPP CP3 — Cathodic Protection Technologist Exam
Corrosion Theory, CP Design, Anodes, Rectifiers, Surveys, Interference &
Coatings
Actual Questions with Answers
1. Define corrosion.
Answer: The deterioration of a material, usually a metal, resulting from a chemical
or electrochemical reaction with its environment.
Rationale: Corrosion is fundamentally an electrochemical process in which a metal
reverts toward its more thermodynamically stable, oxidized (ore-like) state.
2. What four components must be present to form a corrosion cell?
Answer: An anode, a cathode, an electrolyte, and a metallic (electron) path
connecting the anode and cathode.
Rationale: Without all four elements, the electrochemical circuit cannot be
completed and corrosion current cannot flow; removing any one element stops the
corrosion cell from functioning.
3. At the anode of a corrosion cell, what reaction occurs?
Answer: Oxidation occurs — metal atoms lose electrons and go into solution as
metal ions (e.g., Fe → Fe2+ + 2e-).
Rationale: The anode is, by definition, the electrode where oxidation (loss of
electrons) takes place; this is also where metal loss (corrosion) physically occurs.
4. At the cathode of a corrosion cell, what reaction occurs?
Answer: Reduction occurs — electrons are consumed, typically through reactions
such as oxygen reduction or hydrogen evolution, and no metal loss occurs at the
cathode.
Rationale: The cathode is protected from corrosion because it is the site of the
reduction reaction; this principle is the basis for cathodic protection, which forces the
structure to behave as a cathode.
5. What is the difference between oxidation and reduction in electrochemical terms?
Answer: Oxidation is the loss of electrons; reduction is the gain of electrons.
Rationale: The mnemonic 'OIL RIG' (Oxidation Is Loss, Reduction Is Gain) summarizes
this fundamental electrochemical relationship that underlies all corrosion and
cathodic protection reactions.
,6. What is an electrolyte in the context of corrosion?
Answer: A medium (such as soil, water, or concrete pore water) that conducts
electric current through the movement of ions.
Rationale: The electrolyte completes the ionic portion of the corrosion circuit,
allowing current to flow between the anode and cathode through the surrounding
environment rather than through metal alone.
7. What is meant by the term 'half-cell reaction'?
Answer: A chemical equation representing either the oxidation or reduction reaction
occurring at one electrode of an electrochemical cell.
Rationale: Corrosion reactions are often analyzed by separating the overall reaction
into its two half-cell reactions (anodic and cathodic) to better understand electron
transfer.
8. What is the galvanic series, and how is it used?
Answer: A ranked list of metals and alloys according to their relative nobility
(corrosion potential) when immersed in a specific electrolyte (commonly seawater);
it is used to predict which metal will act as the anode when dissimilar metals are
coupled.
Rationale: When two dissimilar metals are electrically connected in the same
electrolyte, the less noble (more active) metal in the galvanic series will corrode
preferentially as the anode.
9. What is galvanic corrosion?
Answer: Accelerated corrosion of a less noble (more active) metal that occurs when
it is electrically coupled to a more noble metal in the presence of an electrolyte.
Rationale: The potential difference between the dissimilar metals drives current flow,
with the more active metal corroding faster than it would alone, while the more
noble metal is cathodically protected.
10. What is the difference between the galvanic series and the electromotive force (EMF)
series?
Answer: The EMF series ranks pure metals under standardized laboratory conditions
based on theoretical standard electrode potentials, while the galvanic series ranks
actual metals and alloys as they behave in a specific real-world electrolyte, such as
seawater.
, Rationale: The galvanic series is more practically useful for corrosion engineering
because it reflects the influence of passive films, alloying, and the actual environment,
which the theoretical EMF series does not capture.
11. What is polarization in the context of corrosion and cathodic protection?
Answer: A change in electrode potential caused by current flow across the
electrode/electrolyte interface, moving the potential away from its natural (open-
circuit) value.
Rationale: Polarization is central to cathodic protection because applying protective
current polarizes the structure's potential in the negative (cathodic) direction, which
is measured to verify protection.
12. Differentiate between activation polarization and concentration polarization.
Answer: Activation polarization results from the energy required to drive the
electrochemical reaction at the electrode surface, while concentration polarization
results from a depletion of reactants (such as oxygen) near the electrode surface
limiting the reaction rate.
Rationale: Understanding which type of polarization dominates helps explain
observed field behavior, such as why oxygen-reduction-controlled cathodic reactions
are strongly influenced by mass transport (concentration polarization) near the metal
surface.
13. What is passivity (a passive film) in corrosion science?
Answer: A thin, adherent, protective oxide film that forms on certain metals (such as
stainless steel or aluminum) and significantly reduces the corrosion rate despite
thermodynamically favorable conditions for corrosion.
Rationale: Passive films act as a barrier that dramatically slows the anodic reaction,
which is why some active metals like aluminum and chromium-containing alloys can
perform well in otherwise corrosive environments.
14. What is pitting corrosion, and why is it considered particularly dangerous?
Answer: A localized form of corrosion that creates small, deep cavities (pits) in an
otherwise largely intact metal surface; it is dangerous because it can cause
unexpected perforation and failure with minimal overall metal loss or visible warning.
Rationale: Because the surrounding surface may appear largely undamaged, pitting
can go undetected until it causes a leak or structural failure, making it one of the
more insidious forms of localized corrosion.
15. What is the difference between uniform (general) corrosion and localized corrosion?
Corrosion Theory, CP Design, Anodes, Rectifiers, Surveys, Interference &
Coatings
Actual Questions with Answers
1. Define corrosion.
Answer: The deterioration of a material, usually a metal, resulting from a chemical
or electrochemical reaction with its environment.
Rationale: Corrosion is fundamentally an electrochemical process in which a metal
reverts toward its more thermodynamically stable, oxidized (ore-like) state.
2. What four components must be present to form a corrosion cell?
Answer: An anode, a cathode, an electrolyte, and a metallic (electron) path
connecting the anode and cathode.
Rationale: Without all four elements, the electrochemical circuit cannot be
completed and corrosion current cannot flow; removing any one element stops the
corrosion cell from functioning.
3. At the anode of a corrosion cell, what reaction occurs?
Answer: Oxidation occurs — metal atoms lose electrons and go into solution as
metal ions (e.g., Fe → Fe2+ + 2e-).
Rationale: The anode is, by definition, the electrode where oxidation (loss of
electrons) takes place; this is also where metal loss (corrosion) physically occurs.
4. At the cathode of a corrosion cell, what reaction occurs?
Answer: Reduction occurs — electrons are consumed, typically through reactions
such as oxygen reduction or hydrogen evolution, and no metal loss occurs at the
cathode.
Rationale: The cathode is protected from corrosion because it is the site of the
reduction reaction; this principle is the basis for cathodic protection, which forces the
structure to behave as a cathode.
5. What is the difference between oxidation and reduction in electrochemical terms?
Answer: Oxidation is the loss of electrons; reduction is the gain of electrons.
Rationale: The mnemonic 'OIL RIG' (Oxidation Is Loss, Reduction Is Gain) summarizes
this fundamental electrochemical relationship that underlies all corrosion and
cathodic protection reactions.
,6. What is an electrolyte in the context of corrosion?
Answer: A medium (such as soil, water, or concrete pore water) that conducts
electric current through the movement of ions.
Rationale: The electrolyte completes the ionic portion of the corrosion circuit,
allowing current to flow between the anode and cathode through the surrounding
environment rather than through metal alone.
7. What is meant by the term 'half-cell reaction'?
Answer: A chemical equation representing either the oxidation or reduction reaction
occurring at one electrode of an electrochemical cell.
Rationale: Corrosion reactions are often analyzed by separating the overall reaction
into its two half-cell reactions (anodic and cathodic) to better understand electron
transfer.
8. What is the galvanic series, and how is it used?
Answer: A ranked list of metals and alloys according to their relative nobility
(corrosion potential) when immersed in a specific electrolyte (commonly seawater);
it is used to predict which metal will act as the anode when dissimilar metals are
coupled.
Rationale: When two dissimilar metals are electrically connected in the same
electrolyte, the less noble (more active) metal in the galvanic series will corrode
preferentially as the anode.
9. What is galvanic corrosion?
Answer: Accelerated corrosion of a less noble (more active) metal that occurs when
it is electrically coupled to a more noble metal in the presence of an electrolyte.
Rationale: The potential difference between the dissimilar metals drives current flow,
with the more active metal corroding faster than it would alone, while the more
noble metal is cathodically protected.
10. What is the difference between the galvanic series and the electromotive force (EMF)
series?
Answer: The EMF series ranks pure metals under standardized laboratory conditions
based on theoretical standard electrode potentials, while the galvanic series ranks
actual metals and alloys as they behave in a specific real-world electrolyte, such as
seawater.
, Rationale: The galvanic series is more practically useful for corrosion engineering
because it reflects the influence of passive films, alloying, and the actual environment,
which the theoretical EMF series does not capture.
11. What is polarization in the context of corrosion and cathodic protection?
Answer: A change in electrode potential caused by current flow across the
electrode/electrolyte interface, moving the potential away from its natural (open-
circuit) value.
Rationale: Polarization is central to cathodic protection because applying protective
current polarizes the structure's potential in the negative (cathodic) direction, which
is measured to verify protection.
12. Differentiate between activation polarization and concentration polarization.
Answer: Activation polarization results from the energy required to drive the
electrochemical reaction at the electrode surface, while concentration polarization
results from a depletion of reactants (such as oxygen) near the electrode surface
limiting the reaction rate.
Rationale: Understanding which type of polarization dominates helps explain
observed field behavior, such as why oxygen-reduction-controlled cathodic reactions
are strongly influenced by mass transport (concentration polarization) near the metal
surface.
13. What is passivity (a passive film) in corrosion science?
Answer: A thin, adherent, protective oxide film that forms on certain metals (such as
stainless steel or aluminum) and significantly reduces the corrosion rate despite
thermodynamically favorable conditions for corrosion.
Rationale: Passive films act as a barrier that dramatically slows the anodic reaction,
which is why some active metals like aluminum and chromium-containing alloys can
perform well in otherwise corrosive environments.
14. What is pitting corrosion, and why is it considered particularly dangerous?
Answer: A localized form of corrosion that creates small, deep cavities (pits) in an
otherwise largely intact metal surface; it is dangerous because it can cause
unexpected perforation and failure with minimal overall metal loss or visible warning.
Rationale: Because the surrounding surface may appear largely undamaged, pitting
can go undetected until it causes a leak or structural failure, making it one of the
more insidious forms of localized corrosion.
15. What is the difference between uniform (general) corrosion and localized corrosion?
