API 571 High Temperature Corrosion 1 — Questions and Answers
Question 1: What is the primary driving force for high-temperature oxidation of metals?
- High chloride concentration
- Elevated partial pressure of oxygen at high temperature (Correct answer)
- Acidic pH in condensate
- Galvanic coupling with noble metals
Correct answer: Elevated partial pressure of oxygen at high temperature
High-temperature oxidation occurs when metals react with oxygen at elevated temperatures, with the rate increasing with oxygen partial pressure and temperature.
Question 2: Above what temperature does carbon steel begin to experience significant oxidation and scaling?
- 300°F (149°C)
- 500°F (260°C)
- 900°F (482°C) (Correct answer)
- 1100°F (593°C)
Correct answer: 900°F (482°C)
Carbon steel begins to form significant oxide scale and suffer measurable metal loss due to oxidation above approximately 900°F (482°C).
Question 3: What is the primary effect of carburization on steel?
- Loss of carbon from the steel surface
- Precipitation of chromium carbides at grain boundaries
- Absorption of carbon increasing hardness and causing embrittlement (Correct answer)
- Formation of sigma phase in austenitic steels
Correct answer: Absorption of carbon increasing hardness and causing embrittlement
Carburization causes carbon absorption into the metal, significantly increasing hardness but severely reducing toughness and ductility of the affected material.
Question 4: Which process involves carbon loss from steel in high-temperature hydrogen-rich atmospheres?
- Carburization
- Decarburization (Correct answer)
- Nitriding
- Sulfidation
Correct answer: Decarburization
Decarburization occurs when hydrogen at high temperature reacts with carbon in steel, reducing surface hardness and strength over time.
Question 5: Above what temperature does sulfidation corrosion by H2S become significant in refinery streams?
- 200°F (93°C)
- 400°F (204°C)
- 500°F (260°C) (Correct answer)
- 800°F (427°C)
Correct answer: 500°F (260°C)
Sulfidation corrosion by hydrogen sulfide becomes significant above approximately 500°F (260°C) where H2S reacts aggressively with iron to form iron sulfide scale.
Question 6: The McConomy curves correlate chromium content of an alloy to predicted rates of which damage mechanism?
- Creep rupture life
- Sulfidation corrosion in hydrogen-free streams (Correct answer)
- Naphthenic acid attack rates
- Hydrogen embrittlement susceptibility
Correct answer: Sulfidation corrosion in hydrogen-free streams
McConomy curves relate alloy chromium content to sulfidation corrosion rates in high-temperature, hydrogen-free process streams.
API 571 High Temperature Corrosion 1
What is the primary driving force for high-temperature oxidation of metals?