API 571 Cheat Sheet 2026

The 30 highest-yield API 571 facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Reheat cracking preferentially occurs in which material during which operation? → Low-alloy Cr-Mo steels during post-weld heat treatment (PWHT)
2. Hydrogen embrittlement (HE) at ambient temperature primarily affects which material property? → Reduces ductility and fracture toughness, enabling brittle fracture at low stress
3. Which API standard is specifically and exclusively dedicated to damage mechanisms affecting fixed equipment in the refining industry? → API 571 — Damage Mechanisms Affecting Fixed Equipment in the Refining Industry
4. What post-weld treatment is most commonly applied to prevent stress corrosion cracking? → Stress relief post-weld heat treatment (PWHT)
5. Which insulation type is generally considered most problematic for CUI due to its high water retention capacity and potential to leach chlorides? → Calcium silicate insulation
6. Which characteristic feature is found on fatigue fracture surfaces that distinguishes them from other failure modes? → Beach marks or clamshell patterns showing crack progression
7. Corrosion under insulation (CUI) is primarily driven by what mechanism? → Moisture penetrating insulation and concentrating corrosive species against the pipe
8. Microbiologically influenced corrosion (MIC) is most commonly caused by which organisms? → Sulfate-reducing bacteria (SRB)
9. Which material is most susceptible to intergranular corrosion after sensitization in the 800–1500°F range? → 304 austenitic stainless steel
10. Remaining creep life assessment for high-temperature equipment uses which analytical approach? → Larson-Miller parameter and creep life fraction calculations based on operating history
11. What is the primary driving force for high-temperature oxidation of metals? → Elevated partial pressure of oxygen at high temperature
12. The Nelson curves published in API 941 are used to define safe operating limits for which damage mechanism? → High Temperature Hydrogen Attack (HTHA)
13. What flow velocity limit is typically imposed on carbon steel piping in anhydrous HF acid service to prevent erosion of the protective iron fluoride scale? → 3 ft/s (0.9 m/s)
14. Hydrogen-induced cracking (HIC) preferentially initiates at which microstructural features? → Non-metallic inclusions and laminations within the steel plate
15. 885°F (475°C) embrittlement is a damage mechanism primarily affecting which steel family? → Ferritic and duplex stainless steels
16. What is the primary corrosion mechanism in refinery amine treating units that causes attack on carbon steel equipment? → Acidic conditions from absorbed CO2 and H2S at elevated temperatures
17. Creep damage in metals is thermally activated and occurs when sustained stress is applied above what temperature fraction of absolute melting point? → 40–50% of absolute melting temperature
18. In HF alkylation units, which material is the preferred choice for many components due to its resistance to hydrofluoric acid? → Monel 400 (Ni-Cu alloy)
19. Chloride stress corrosion cracking (Cl-SCC) in austenitic stainless steel requires what combination of conditions? → Tensile stress, chlorides, and temperature above ~140°F
20. Which alloying additions most effectively extend Nelson curve limits and improve resistance to HTHA? → Chromium and molybdenum additions
21. Which of the following is NOT considered a high-temperature damage mechanism in API 571? → Chloride stress corrosion cracking
22. Polythionic acid SCC (PTASCC) in refineries affects which material during which condition? → Sensitized austenitic stainless steels during shutdowns in sulfur service
23. Stepwise cracking (SWC) in API 571 describes which crack morphology? → HIC cracks connecting in a staircase pattern progressing through the vessel or pipe wall
24. Caustic stress corrosion cracking (caustic embrittlement) in carbon steel is most likely to occur when NaOH concentrations exceed approximately: → 10–30 wt%
25. Baking (dehydrogenation heat treatment) is applied after electroplating or welding to accomplish what? → Remove absorbed hydrogen before it can cause delayed cracking
26. Liquid metal embrittlement (LME) can occur when carbon steel or other metals contact which substances? → Liquid mercury or molten zinc
27. What is the primary damage mechanism for carbon steel in amine treating systems? → Amine corrosion from degradation products and stress corrosion cracking
28. Carbonate cracking in refinery systems is associated with which type of environment? → Alkaline carbonate/bicarbonate solutions in FCC and amine units
29. What corrosion rate threshold typically triggers increased inspection frequency under API 510? → Greater than 0.010 in/yr
30. What operational change most effectively reduces the risk of HTHA in process equipment? → Lowering operating temperature and/or hydrogen partial pressure below the Nelson curve