Corrosion Mechanisms & Damage Assessment Flashcards
7 cards from real API 510 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Corrosion Mechanisms & Damage Assessment flashcards as text
What is the primary concern with high-temperature hydrogen attack (HTHA) in pressure vessels?
Answer: Decarburization and fissuring that weaken the steel permanently
HTHA causes decarburization and internal fissuring as atomic hydrogen reacts with carbides in the steel, permanently reducing strength and ductility.
An inspector observes a vessel operating in wet H₂S service. Which damage mechanism should be the primary concern?
Answer: Sulfide stress cracking (SSC)
Wet H₂S service promotes sulfide stress cracking, especially in high-strength or hardened steels, and is a critical concern per API 510 and NACE standards.
What is the significance of the 'corrosion allowance' in pressure vessel design and inspection?
Answer: It is extra metal thickness added to account for expected corrosion over the vessel's service life
Corrosion allowance is the additional thickness beyond the calculated minimum to accommodate anticipated metal loss during the design service life.
In API 510, what calculation determines the remaining corrosion allowance for an in-service vessel?
Answer: Actual measured thickness minus required minimum thickness
Remaining corrosion allowance equals the actual measured thickness minus the required minimum thickness (t_minimum), indicating how much additional metal loss is acceptable.
Galvanic corrosion between two dissimilar metals is most likely to occur when:
Answer: The metals are in electrical contact in the presence of an electrolyte
Galvanic corrosion requires electrical contact between dissimilar metals and an electrolyte (conductive liquid) to complete the electrochemical cell.
Which material condition makes a vessel most susceptible to brittle fracture during startup in cold weather?
Answer: Low Charpy impact toughness at low operating temperatures
Low Charpy impact toughness at low temperatures means the steel cannot absorb sufficient energy to prevent crack propagation, making brittle fracture likely.
In API 510, 'localized corrosion' detected during inspection is typically evaluated using:
Answer: Point thickness measurements in the corroded area compared to t_minimum
Localized corrosion is assessed by comparing the minimum thickness measured within the affected area to the calculated minimum required thickness (t_minimum).