SPED Corrosion Prevention & Protection 3 — Questions and Answers
Question 1: In impressed current cathodic protection (ICCP) systems, what device converts AC power to DC and controls the output current?
- Transformer
- Rectifier (Correct answer)
- Sacrificial anode
- Reference cell
Correct answer: Rectifier
A rectifier converts AC utility power to DC and allows adjustment of voltage and current output to maintain adequate cathodic protection levels.
Question 2: What is the purpose of a test station installed along a cathodically protected pipeline?
- To inject corrosion inhibitors into the product stream
- To allow pipe-to-soil potential measurements without excavation (Correct answer)
- To bond parallel pipelines together
- To mark the pipeline right-of-way
Correct answer: To allow pipe-to-soil potential measurements without excavation
Test stations provide accessible connection points so technicians can measure pipe-to-soil potentials and monitor cathodic protection effectiveness without excavating.
Question 3: Which form of corrosion preferentially attacks grain boundaries in a metal?
- Galvanic corrosion
- Pitting corrosion
- Intergranular corrosion (Correct answer)
- Crevice corrosion
Correct answer: Intergranular corrosion
Intergranular corrosion attacks along grain boundaries where chromium depletion or precipitates create locally anodic zones, common in improperly heat-treated stainless steels.
Question 4: Hydrogen-induced cracking (HIC) in pipelines is most commonly associated with which environment?
- Dry nitrogen service
- Wet H2S (sour) service (Correct answer)
- High-temperature steam
- Alkaline cleaning solutions
Correct answer: Wet H2S (sour) service
HIC occurs in wet H2S (sour) service where atomic hydrogen generated at the pipe surface diffuses into the steel and recombines at internal defects, creating internal pressure and cracking.
Question 5: What is the primary purpose of adding a corrosion inhibitor to a pipeline carrying wet natural gas?
- Increase product flow rate
- Form a protective film on the pipe interior surface (Correct answer)
- Remove water from the gas stream
- Reduce operating pressure
Correct answer: Form a protective film on the pipe interior surface
Corrosion inhibitors adsorb onto the metal surface to form a protective film that reduces the rate of electrochemical corrosion reactions.
Question 6: Which type of soil condition is most corrosive to buried carbon steel pipelines?
- Dry sandy soil with high resistivity
- Moist clay soil with low resistivity and low pH (Correct answer)
- Gravelly well-drained soil
- Calcareous soil with high pH
Correct answer: Moist clay soil with low resistivity and low pH
Moist clay soils with low electrical resistivity and low pH provide good electrolyte conductivity and aggressive chemistry, creating highly corrosive conditions for buried steel.
Question 7: What is the function of a decoupler (DC decoupler / isolating device) installed in a cathodic protection circuit?
- Blocks DC current while allowing AC current to pass for safety grounding (Correct answer)
- Converts DC to AC for power distribution
- Measures pipe-to-soil potential continuously
- Prevents lightning damage to rectifiers
Correct answer: Blocks DC current while allowing AC current to pass for safety grounding
DC decouplers block DC cathodic protection current from leaking across isolation joints while passing AC fault current and lightning to ground for safety.
SPED Corrosion Prevention & Protection 3
In impressed current cathodic protection (ICCP) systems, what device converts AC power to DC and controls the output current?