Practice Test Geeks(API) American Petroleum Institute Certification Practice Test
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Corrosion & Damage Mechanisms Flashcards

7 cards from real API practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. API 571 identifies microbiologically influenced corrosion (MIC) as being caused primarily by which type of organism in stagnant or low-flow aqueous systems?

    Answer: Sulfate-reducing bacteria (SRB) that generate hydrogen sulfide

    Sulfate-reducing bacteria (SRB) are the primary culprits in MIC in oil and gas systems; they reduce sulfate to sulfide, creating locally corrosive conditions and H₂S under deposits even in anaerobic environments.

  2. In API 571, which damage mechanism is described as the preferential corrosion of welds due to differences in microstructure, residual stress, or composition between the weld metal and base metal?

    Answer: Weld decay (weld corrosion)

    Weld decay (or weld corrosion) refers to preferential attack of welds or heat-affected zones due to microstructural differences, sensitization, or residual stresses compared to the surrounding base metal.

  3. According to API 571, dealloying (selective leaching) most commonly affects which alloy system in petroleum industry service?

    Answer: Copper-zinc alloys (brass) where zinc is selectively removed (dezincification)

    Dezincification is the most common form of dealloying in the petroleum industry, where zinc is selectively dissolved from brass alloys leaving a porous copper-rich structure with drastically reduced mechanical properties.

  4. Which damage mechanism described in API 571 can occur when a liquid metal contacts a stressed or susceptible solid metal, causing rapid embrittlement and cracking?

    Answer: Liquid metal embrittlement (LME)

    Liquid metal embrittlement (LME) occurs when certain liquid metals (e.g., zinc, mercury, cadmium) contact a susceptible solid metal under tensile stress, causing rapid intergranular crack propagation.

  5. In API 571, high-temperature hydrogen attack (HTHA) is most accurately described as what type of damage to carbon and low-alloy steels?

    Answer: Methane formation from hydrogen reacting with carbides, causing fissuring and decarburization

    HTHA occurs when hydrogen reacts with iron carbides at elevated temperature and pressure to form methane gas, which cannot diffuse out and builds up pressure causing internal fissures and decarburization.

  6. API 571 recommends using Nelson Curves (from API RP 941) for determining safe operating limits against which damage mechanism?

    Answer: High-temperature hydrogen attack (HTHA)

    Nelson Curves, published in API RP 941, define safe operating temperature and partial pressure limits for carbon and alloy steels to avoid high-temperature hydrogen attack (HTHA).

  7. According to API 571, which damage mechanism is characterized by cyclic stresses from temperature fluctuations causing crack initiation and propagation in metals, typically at stress concentration points?

    Answer: Thermal fatigue

    Thermal fatigue results from cyclic thermal stresses induced by repeated temperature changes, causing crack initiation at stress concentrations such as notches, welds, or geometric discontinuities.