API 571 High Temperature Corrosion 3

Question 1

Creep damage in metals occurs when sustained stress is applied at temperatures above what fraction of the absolute melting temperature?

Accepted Answer

40–50% of Tm

Answer

Creep becomes significant when metals are under sustained stress at temperatures above approximately 40–50% of their absolute melting temperature.

Question 2

Which alloying element provides the greatest improvement in high-temperature oxidation resistance by forming a protective oxide scale?

Accepted Answer

Chromium

Answer

Chromium forms a dense, adherent Cr2O3 oxide scale that acts as a diffusion barrier, significantly reducing oxidation rates at high temperatures.

Question 3

Thermal fatigue in process equipment is caused by which fundamental mechanism?

Accepted Answer

Cyclic temperature changes generating repeated thermal expansion and contraction stresses

Answer

Thermal fatigue results from repeated thermal cycling that induces cyclic stresses due to differential thermal expansion and contraction, eventually initiating cracks.

Question 4

Fuel ash corrosion (vanadium attack) primarily affects which type of equipment?

Accepted Answer

Fired heater tubes and boiler components above 1000°F

Answer

Vanadium pentoxide and sodium sulfate ash deposits attack fired heater tubes and boiler components at temperatures above 1000°F, causing aggressive fluxing corrosion.

Question 5

Which damage mechanism converts metal into a powder of metal particles, oxides, and carbon through a catastrophic carburization reaction?

Accepted Answer

Metal dusting

Answer

Metal dusting is a catastrophic form of carburization in which steel disintegrates into a dust of metal, oxides, and carbon due to supersaturated carbon activity in the gas.

API 571 - API 571 Corrosion and Materials Practice Test

API 571 - API 571 Corrosion and Materials Practice Test

API 571 High Temperature Corrosion 3