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 'creep' damage in the context of API 510 pressure vessel inspection?
Answer: Slow progressive plastic deformation under sustained stress at elevated temperature
Creep is the time-dependent plastic deformation that occurs when metal is subjected to sustained stress at temperatures above its creep threshold.
An API 510 inspector identifies 'blistering' on the interior of a carbon steel vessel in wet H₂S service. What is the most likely cause?
Answer: Hydrogen pressure buildup at internal laminations or inclusions
In wet H₂S service, atomic hydrogen diffuses into steel and collects at voids or laminations, building sufficient pressure to form surface blisters.
Which corrosion rate formula is used in API 510 to calculate the short-term corrosion rate?
Answer: (Previous thickness - Current thickness) / Years between inspections
The short-term corrosion rate uses only the most recent inspection interval: (previous measured thickness − current measured thickness) ÷ years between the two inspections.
Intergranular corrosion in austenitic stainless steel is most commonly caused by:
Answer: Sensitization from heating in the range of 800°F to 1500°F
Sensitization occurs when chromium carbides precipitate at grain boundaries, depleting adjacent zones of chromium and making them susceptible to intergranular attack.
What is 'crevice corrosion' and where is it most likely to occur on a pressure vessel?
Answer: Localized attack in confined spaces where stagnant solution becomes aggressive, such as under gaskets or deposits
Crevice corrosion occurs in confined spaces where stagnant solution becomes depleted of oxygen or enriched in corrosive ions, creating a differential concentration cell.
In API 510, when evaluating a vessel with general corrosion, the inspector should compare the measured thickness to:
Answer: The calculated minimum required thickness (t_min) based on MAWP and code formulas
API 510 requires comparing actual measured thickness to the minimum thickness calculated from the MAWP using the applicable code formula, not the original design thickness.
What is the primary difference between 'erosion' and 'corrosion' as damage mechanisms in pressure vessels?
Answer: Erosion is mechanical removal of material, corrosion is electrochemical or chemical attack
Erosion involves the mechanical removal of metal by solid particles, fluid flow, or cavitation, while corrosion involves chemical or electrochemical reactions that degrade the metal.