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. According to API 571, which damage mechanism is characterized by cracking that occurs in high-strength steels exposed to hydrogen-containing environments under sustained tensile stress?

    Answer: Sulfide stress cracking (SSC)

    Sulfide stress cracking (SSC) occurs in high-strength steels under tensile stress in hydrogen sulfide (H₂S) environments, and is a primary concern addressed by NACE MR0175/ISO 15156.

  2. Which type of corrosion preferentially attacks grain boundaries in a metal, often as a result of sensitization in austenitic stainless steels?

    Answer: Intergranular corrosion

    Intergranular corrosion attacks along grain boundaries, commonly occurring in sensitized austenitic stainless steels where chromium carbides precipitate and deplete chromium from the grain boundary regions.

  3. In API 571 terminology, which high-temperature damage mechanism involves the diffusion of carbon from a steel into an adjacent higher-alloy steel or weld material?

    Answer: Decarburization

    Decarburization involves the loss of carbon from the surface layer of steel at elevated temperatures, reducing hardness and strength in the affected zone.

  4. Which damage mechanism described in API 571 is caused by the condensation of ammonium bisulfide in refinery overhead systems, resulting in aggressive corrosion?

    Answer: Ammonium bisulfide corrosion

    Ammonium bisulfide (NH₄HS) corrosion occurs in refinery crude unit overhead and hydroprocessing systems when ammonium bisulfide deposits and attacks carbon and alloy steels.

  5. According to API 571, at what minimum temperature (°F) does high-temperature oxidation of carbon steel typically become a significant concern?

    Answer: 900°F (482°C)

    High-temperature oxidation of carbon steel becomes significant above approximately 900°F (482°C), where the oxidation rate increases substantially and protective oxide scales may break down.

  6. Which API 571 damage mechanism results from the absorption of atomic hydrogen into steel during corrosion reactions, leading to blistering, stepwise cracking, or stress-oriented cracking?

    Answer: Wet H₂S damage

    Wet H₂S damage is a broad term covering hydrogen blistering, hydrogen-induced cracking (HIC), stress-oriented hydrogen-induced cracking (SOHIC), and sulfide stress cracking (SSC), all caused by hydrogen absorption in wet H₂S service.

  7. In API 571, naphthenic acid corrosion is most commonly associated with which process condition?

    Answer: High-temperature crude distillation above 450°F with high total acid number (TAN) crudes

    Naphthenic acid corrosion occurs at elevated temperatures (typically 450–750°F) when processing high TAN crude oils, affecting carbon steel and even some stainless steels in distillation units.