PHMSA Corrosion Control of Pipeline Systems Exam Prep |
Practice Questions & Answers with Detailed Rationales
Exam Coverage Summary (Point Form)
I. Fundamentals of Pipeline Corrosion
Electrochemical nature of corrosion (anode, cathode, electrolyte, metallic path)
Types: Uniform (general), Galvanic, Pitting, Crevice, Microbiologically Influenced (MIC)
Sweet corrosion (CO₂) and Sour corrosion (H₂S)
Factors influencing corrosion rates (soil resistivity, moisture, pH, temperature)
Atmospheric and stray current corrosion
Corrosion under insulation
II. External Corrosion Control
Protective coatings: purpose, types, application requirements
Coating holidays: detection, causes, consequences
Cathodic Protection (CP): Principles and types
Sacrificial anodes (galvanic): magnesium, zinc
Impressed current systems: rectifiers, anodes, power sources
CP criteria: -0.85 V vs. Cu-CuSO₄ reference electrode
Testing and monitoring: annual CP testing requirement
Soil resistivity and its effect on CP design
Electrical isolation, bonds, and test leads
III. Internal Corrosion Control
Corrosive substances: water, CO₂, H₂S, acids
Sweet corrosion: carbonic acid formation from CO₂ + water
Sour corrosion: H₂S reaction forming iron sulfide
Microbiologically Influenced Corrosion (MIC): bacteria and biofilms
Monitoring methods: fluid sampling, inspection tools, corrosion coupons
Corrosion inhibitors and mitigation strategies
Dehydration and water removal
IV. Regulatory Framework & Compliance
49 CFR Part 192 (Gas pipelines) Subpart I - Corrosion Control
49 CFR Part 195 (Hazardous liquids) Subpart H - Corrosion Control
AMPP/NACE Standards: SP0206, SP0502 (incorporated by reference effective Jan 2027)
Coating requirements: new pipe installed after July 31, 1971
, CP installation timeline: within one year after construction
Records and documentation requirements
V. Monitoring, Inspection & Integrity
In-line inspection (ILI) tools: MFL, ultrasonic
Direct examination of exposed pipe
Potential measurements and reference electrodes
Corrosion coupons and test coupons
Stray current and interference current mitigation
Evaluation and repair of corroded pipe
Remaining life assessment
Shorted casings and electrical isolation issues
250
Questions 1-25: Fundamentals & Electrochemistry
1. A pipeline technician observes uniform thinning across an entire exposed pipe section during
an inspection. What type of corrosion mechanism is most likely responsible?
A. Pitting corrosion
B. Galvanic corrosion
C. General or uniform corrosion
D. Crevice corrosion
Answer: C
Rationale: General or uniform corrosion causes relatively even metal loss across the entire
exposed surface. Pitting creates localized holes, galvanic requires dissimilar metals, and
crevice occurs in confined spaces.
2. During an integrity assessment, a gas operator finds small holes penetrating deeply into the
pipe wall while the surrounding areas appear unaffected. Which localized corrosion
mechanism should be documented as the primary cause?
A. Uniform corrosion
B. Sour corrosion
C. Pitting corrosion
D. Erosion corrosion
Answer: C
Rationale: Pitting corrosion is characterized by small, localized holes or cavities that
, penetrate deeply while surrounding metal remains intact, making it particularly dangerous
and difficult to detect.
3. A buried steel pipeline is connected to a magnesium anode. The magnesium corrodes
preferentially, protecting the steel pipe. What is this corrosion protection method called?
A. Impressed current cathodic protection
B. Sacrificial anodic protection
C. Barrier protection
D. Passivation
Answer: B
Rationale: This is sacrificial (galvanic) anodic protection where a more active metal
(magnesium) corrodes instead of the protected steel pipeline.
4. An operator discovers that a section of pipeline is electrically connected to a copper
grounding system in moist soil. The steel pipe is showing accelerated corrosion. What
corrosion mechanism is occurring?
A. Atmospheric corrosion
B. Galvanic corrosion
C. Sweet corrosion
D. Uniform corrosion
Answer: B
Rationale: Galvanic corrosion occurs when two dissimilar metals are in electrical contact in
a conductive electrolyte. The more active metal (steel) corrodes preferentially when
connected to a more noble metal (copper).
5. During a coating survey, a technician identifies a small area where the external coating is
damaged, exposing bare metal. Soil moisture and electrolytes are present. Which element of
the corrosion cell is represented by the exposed bare metal?
A. Electrolyte
B. Cathode
C. Anode
D. Metallic path
Answer: C
Rationale: The exposed bare metal at the coating defect typically becomes the anode where
metal loss (corrosion) occurs, while the surrounding coated area serves as the cathode.
6. A pipeline in an area with high chloride concentration in the soil is experiencing accelerated
localized attack. What type of corrosion is most likely occurring?
A. Sweet corrosion
, B. Sour corrosion
C. Pitting corrosion
D. Uniform corrosion
Answer: C
Rationale: Chlorides break down protective oxide films on metal surfaces, initiating localized
pitting corrosion, particularly aggressive for carbon steel pipelines in high chloride
environments.
7. An operator detects carbon dioxide and water in a natural gas stream. What type of internal
corrosion is most likely to develop?
A. Sour corrosion
B. Sweet corrosion
C. MIC
D. Atmospheric corrosion
Answer: B
Rationale: Sweet corrosion refers to CO₂ corrosion where carbon dioxide dissolves in water
to form carbonic acid, which attacks carbon steel pipelines.
8. During internal inspection, iron sulfide scale is found on the inner pipe wall. The transported
product contains hydrogen sulfide. What corrosion mechanism is occurring?
A. Sweet corrosion
B. Sour corrosion
C. Galvanic corrosion
D. Pitting corrosion
Answer: B
Rationale: Sour corrosion occurs when H₂S reacts with iron to form iron sulfide scale, which
can be protective or corrosive depending on conditions.
9. An operator is evaluating a pipeline where biofilms are found on the internal surface.
Bacterial activity is suspected of accelerating corrosion. What type of corrosion should be
investigated?
A. Sweet corrosion
B. Sour corrosion
C. Microbiologically Influenced Corrosion (MIC)
D. Stray current corrosion
Answer: C
Rationale: MIC occurs when bacteria and other microorganisms accelerate the corrosion
process, often forming biofilms that create localized environments conducive to corrosion.
Practice Questions & Answers with Detailed Rationales
Exam Coverage Summary (Point Form)
I. Fundamentals of Pipeline Corrosion
Electrochemical nature of corrosion (anode, cathode, electrolyte, metallic path)
Types: Uniform (general), Galvanic, Pitting, Crevice, Microbiologically Influenced (MIC)
Sweet corrosion (CO₂) and Sour corrosion (H₂S)
Factors influencing corrosion rates (soil resistivity, moisture, pH, temperature)
Atmospheric and stray current corrosion
Corrosion under insulation
II. External Corrosion Control
Protective coatings: purpose, types, application requirements
Coating holidays: detection, causes, consequences
Cathodic Protection (CP): Principles and types
Sacrificial anodes (galvanic): magnesium, zinc
Impressed current systems: rectifiers, anodes, power sources
CP criteria: -0.85 V vs. Cu-CuSO₄ reference electrode
Testing and monitoring: annual CP testing requirement
Soil resistivity and its effect on CP design
Electrical isolation, bonds, and test leads
III. Internal Corrosion Control
Corrosive substances: water, CO₂, H₂S, acids
Sweet corrosion: carbonic acid formation from CO₂ + water
Sour corrosion: H₂S reaction forming iron sulfide
Microbiologically Influenced Corrosion (MIC): bacteria and biofilms
Monitoring methods: fluid sampling, inspection tools, corrosion coupons
Corrosion inhibitors and mitigation strategies
Dehydration and water removal
IV. Regulatory Framework & Compliance
49 CFR Part 192 (Gas pipelines) Subpart I - Corrosion Control
49 CFR Part 195 (Hazardous liquids) Subpart H - Corrosion Control
AMPP/NACE Standards: SP0206, SP0502 (incorporated by reference effective Jan 2027)
Coating requirements: new pipe installed after July 31, 1971
, CP installation timeline: within one year after construction
Records and documentation requirements
V. Monitoring, Inspection & Integrity
In-line inspection (ILI) tools: MFL, ultrasonic
Direct examination of exposed pipe
Potential measurements and reference electrodes
Corrosion coupons and test coupons
Stray current and interference current mitigation
Evaluation and repair of corroded pipe
Remaining life assessment
Shorted casings and electrical isolation issues
250
Questions 1-25: Fundamentals & Electrochemistry
1. A pipeline technician observes uniform thinning across an entire exposed pipe section during
an inspection. What type of corrosion mechanism is most likely responsible?
A. Pitting corrosion
B. Galvanic corrosion
C. General or uniform corrosion
D. Crevice corrosion
Answer: C
Rationale: General or uniform corrosion causes relatively even metal loss across the entire
exposed surface. Pitting creates localized holes, galvanic requires dissimilar metals, and
crevice occurs in confined spaces.
2. During an integrity assessment, a gas operator finds small holes penetrating deeply into the
pipe wall while the surrounding areas appear unaffected. Which localized corrosion
mechanism should be documented as the primary cause?
A. Uniform corrosion
B. Sour corrosion
C. Pitting corrosion
D. Erosion corrosion
Answer: C
Rationale: Pitting corrosion is characterized by small, localized holes or cavities that
, penetrate deeply while surrounding metal remains intact, making it particularly dangerous
and difficult to detect.
3. A buried steel pipeline is connected to a magnesium anode. The magnesium corrodes
preferentially, protecting the steel pipe. What is this corrosion protection method called?
A. Impressed current cathodic protection
B. Sacrificial anodic protection
C. Barrier protection
D. Passivation
Answer: B
Rationale: This is sacrificial (galvanic) anodic protection where a more active metal
(magnesium) corrodes instead of the protected steel pipeline.
4. An operator discovers that a section of pipeline is electrically connected to a copper
grounding system in moist soil. The steel pipe is showing accelerated corrosion. What
corrosion mechanism is occurring?
A. Atmospheric corrosion
B. Galvanic corrosion
C. Sweet corrosion
D. Uniform corrosion
Answer: B
Rationale: Galvanic corrosion occurs when two dissimilar metals are in electrical contact in
a conductive electrolyte. The more active metal (steel) corrodes preferentially when
connected to a more noble metal (copper).
5. During a coating survey, a technician identifies a small area where the external coating is
damaged, exposing bare metal. Soil moisture and electrolytes are present. Which element of
the corrosion cell is represented by the exposed bare metal?
A. Electrolyte
B. Cathode
C. Anode
D. Metallic path
Answer: C
Rationale: The exposed bare metal at the coating defect typically becomes the anode where
metal loss (corrosion) occurs, while the surrounding coated area serves as the cathode.
6. A pipeline in an area with high chloride concentration in the soil is experiencing accelerated
localized attack. What type of corrosion is most likely occurring?
A. Sweet corrosion
, B. Sour corrosion
C. Pitting corrosion
D. Uniform corrosion
Answer: C
Rationale: Chlorides break down protective oxide films on metal surfaces, initiating localized
pitting corrosion, particularly aggressive for carbon steel pipelines in high chloride
environments.
7. An operator detects carbon dioxide and water in a natural gas stream. What type of internal
corrosion is most likely to develop?
A. Sour corrosion
B. Sweet corrosion
C. MIC
D. Atmospheric corrosion
Answer: B
Rationale: Sweet corrosion refers to CO₂ corrosion where carbon dioxide dissolves in water
to form carbonic acid, which attacks carbon steel pipelines.
8. During internal inspection, iron sulfide scale is found on the inner pipe wall. The transported
product contains hydrogen sulfide. What corrosion mechanism is occurring?
A. Sweet corrosion
B. Sour corrosion
C. Galvanic corrosion
D. Pitting corrosion
Answer: B
Rationale: Sour corrosion occurs when H₂S reacts with iron to form iron sulfide scale, which
can be protective or corrosive depending on conditions.
9. An operator is evaluating a pipeline where biofilms are found on the internal surface.
Bacterial activity is suspected of accelerating corrosion. What type of corrosion should be
investigated?
A. Sweet corrosion
B. Sour corrosion
C. Microbiologically Influenced Corrosion (MIC)
D. Stray current corrosion
Answer: C
Rationale: MIC occurs when bacteria and other microorganisms accelerate the corrosion
process, often forming biofilms that create localized environments conducive to corrosion.
