API 571 High Temperature Corrosion

Question 1

What is the primary driving force for high-temperature oxidation of metals?

Accepted Answer

Elevated partial pressure of oxygen at high temperature

Answer

High chloride concentration

Answer

Acidic pH in condensate

Answer

Galvanic coupling with noble metals

Question 2

Above what temperature does carbon steel begin to experience significant oxidation and scaling?

Accepted Answer

900°F (482°C)

Answer

300°F (149°C)

Answer

500°F (260°C)

Answer

1100°F (593°C)

Question 3

What is the primary effect of carburization on steel?

Accepted Answer

Absorption of carbon increasing hardness and causing embrittlement

Answer

Loss of carbon from the steel surface

Answer

Precipitation of chromium carbides at grain boundaries

Answer

Formation of sigma phase in austenitic steels

Question 4

Which process involves carbon loss from steel in high-temperature hydrogen-rich atmospheres?

Accepted Answer

Decarburization

Answer

Carburization

Answer

Nitriding

Answer

Sulfidation

Question 5

Above what temperature does sulfidation corrosion by H2S become significant in refinery streams?

Accepted Answer

500°F (260°C)

Answer

200°F (93°C)

Answer

400°F (204°C)

Answer

800°F (427°C)

Question 6

The McConomy curves correlate chromium content of an alloy to predicted rates of which damage mechanism?

Accepted Answer

Sulfidation corrosion in hydrogen-free streams

Answer

Creep rupture life

Answer

Naphthenic acid attack rates

Answer

Hydrogen embrittlement susceptibility