SPED Corrosion Prevention & Protection 2 — Questions and Answers
Question 1: Which type of corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte?
- Crevice corrosion
- Galvanic corrosion (Correct answer)
- Erosion corrosion
- Intergranular corrosion
Correct answer: Galvanic corrosion
Galvanic corrosion occurs when dissimilar metals form an electrochemical cell in the presence of an electrolyte, causing the anodic metal to corrode preferentially.
Question 2: In cathodic protection, which component of the system is intentionally corroded to protect the structure?
- Cathode
- Reference electrode
- Anode (Correct answer)
- Rectifier
Correct answer: Anode
In cathodic protection, the anode (sacrificial or impressed current) oxidizes and corrodes to supply protective current to the cathode (the structure being protected).
Question 3: What is the primary mechanism by which fusion-bonded epoxy (FBE) coating protects buried pipelines?
- Providing cathodic protection current
- Acting as a physical barrier to moisture and oxygen (Correct answer)
- Neutralizing soil acidity
- Absorbing hydrogen sulfide
Correct answer: Acting as a physical barrier to moisture and oxygen
FBE coatings protect pipelines primarily by acting as a physical barrier that prevents moisture, oxygen, and electrolytes from reaching the pipe surface.
Question 4: Which parameter is used to verify adequate cathodic protection of a pipeline per NACE SP0169?
- -0.650 V vs. CSE
- -0.850 V vs. CSE (Correct answer)
- -1.200 V vs. CSE
- -0.500 V vs. CSE
Correct answer: -0.850 V vs. CSE
NACE SP0169 specifies a minimum pipe-to-soil potential of -0.850 V (vs. copper-copper sulfate electrode) as the criterion for adequate cathodic protection.
Question 5: Stress corrosion cracking (SCC) in pipelines requires which three conditions to occur simultaneously?
- High pressure, low temperature, and acidic pH
- Susceptible material, tensile stress, and corrosive environment (Correct answer)
- Elevated temperature, hydrogen, and compressive stress
- Soil bacteria, moisture, and cathodic protection
Correct answer: Susceptible material, tensile stress, and corrosive environment
SCC requires the simultaneous presence of a susceptible material, sufficient tensile stress, and a specific corrosive environment — remove any one and SCC cannot initiate.
Question 6: What type of corrosion is characterized by localized attack that forms pits on the metal surface?
- Uniform corrosion
- Erosion corrosion
- Pitting corrosion (Correct answer)
- Exfoliation corrosion
Correct answer: Pitting corrosion
Pitting corrosion is a localized form that creates small cavities or pits penetrating deep into the metal while the surrounding surface remains relatively unaffected.
Question 7: Which coating system is typically selected for high-temperature buried pipelines operating above 65°C (150°F)?
- Polyethylene tape wrap
- Coal tar enamel
- Fusion-bonded epoxy
- Three-layer polyolefin with high-temperature primer (Correct answer)
Correct answer: Three-layer polyolefin with high-temperature primer
Three-layer polyolefin systems with high-temperature-rated primers are selected for buried pipelines above 65°C because standard FBE and tape coatings can disbond at elevated temperatures.
SPED Corrosion Prevention & Protection 2
Which type of corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte?