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
Which API 510 inspection finding would most directly indicate active under-deposit corrosion?
Answer: Localized thinning beneath fouling deposits when deposits are removed
Under-deposit corrosion occurs beneath scale, fouling, or biological deposits where trapped moisture and aggressive species concentrate, causing localized thinning.
Thermal fatigue damage in pressure vessels is primarily caused by:
Answer: Cyclic thermal stresses from repeated heating and cooling
Thermal fatigue results from cyclic thermal stresses that occur when temperature fluctuations cause differential expansion and contraction, eventually initiating cracks.
During API 510 fitness-for-service assessment of a corroded vessel, a 'remaining life' calculation requires which two key inputs?
Answer: Remaining corrosion allowance and the applicable corrosion rate
Remaining life is calculated as remaining corrosion allowance (actual thickness − t_minimum) divided by the applicable corrosion rate.
What is 'amine stress corrosion cracking' and which vessel service is most at risk?
Answer: Cracking in carbon steel vessels handling amine solutions used in gas treating
Amine stress corrosion cracking occurs in carbon steel exposed to amine solutions (MEA, DEA, MDEA) used in gas sweetening, particularly in weld heat-affected zones under residual stress.
Polythionic acid stress corrosion cracking (PTASCC) is a special concern during:
Answer: Shutdown, maintenance, and startup when sensitized austenitic stainless steel contacts moisture and air
PTASCC forms when iron sulfide scale on sensitized austenitic stainless steel reacts with oxygen and moisture during shutdown, creating polythionic acids that attack grain boundaries.
An API 510 inspector notices that wall thinning is concentrated in the bottom third of a horizontal vessel in aqueous service. What is the most likely explanation?
Answer: Water dropout and settling causing accelerated corrosion at the liquid-vapor interface and bottom
In horizontal vessels handling wet streams, water settles to the bottom, creating concentrated corrosive conditions and accelerated wall loss in that zone.
Which condition is required for 'microbiologically influenced corrosion' (MIC) to occur in a pressure vessel?
Answer: Presence of microorganisms, typically in stagnant or low-flow aqueous conditions
MIC requires living microorganisms (bacteria, fungi) in an aqueous environment, typically in stagnant or low-flow conditions where colonies can establish and create aggressive local chemistry.