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

10% of Tm

Answer

25% of Tm

Answer

75% of Tm

Question 2

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

Accepted Answer

Chromium

Answer

Molybdenum

Answer

Nickel

Answer

Vanadium

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

Uniform sustained high-temperature operation

Answer

Overloading beyond the material's tensile strength

Answer

Chemical attack at grain boundaries during heating

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

Process vessels operating below 500°F

Answer

Buried underground pipelines

Answer

Atmospheric storage tanks

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

Decarburization

Answer

Carburization

Answer

Nitriding

Question 6

The Nelson curves published in API 941 are used to define safe operating limits for which damage mechanism?

Accepted Answer

High Temperature Hydrogen Attack (HTHA)

Answer

Sulfidation corrosion

Answer

Naphthenic acid corrosion

Answer

Temper embrittlement