API 571 Mechanical and Metallurgical Failures 2

Question 1

Creep damage in metals is thermally activated and occurs when sustained stress is applied above what temperature fraction of absolute melting point?

Accepted Answer

40–50% of absolute melting temperature

Answer

Creep becomes significant when metals operate above approximately 40–50% of their absolute melting temperature (Tm) under sustained stress.

Question 2

Which stage of creep directly precedes and leads to fracture?

Accepted Answer

Tertiary creep with accelerating strain rate and void coalescence

Answer

Tertiary creep is characterized by accelerating deformation due to microstructural damage accumulation — void growth, coalescence, and necking — that terminates in fracture.

Question 3

How does stress rupture differ from classic long-term creep?

Accepted Answer

Stress rupture occurs at higher stress levels with shorter time to failure

Answer

Stress rupture is a form of high-stress creep failure that occurs in a relatively short time at stresses near or above the yield strength at elevated temperature.

Question 4

885°F (475°C) embrittlement in ferritic stainless steels is caused by precipitation of which phase?

Accepted Answer

Alpha-prime chromium-rich phase in the BCC matrix

Answer

Alpha-prime, a chromium-rich BCC phase, precipitates in high-chromium ferritic stainless steels near 475°C through spinodal decomposition, causing severe embrittlement at room temperature.

Question 5

What microstructural change occurs during graphitization of carbon steel at elevated temperatures?

Accepted Answer

Iron carbides transform to graphite nodules, reducing toughness and strength

Answer

Graphitization at temperatures above ~800°F causes iron carbides (Fe3C) to decompose into graphite nodules, creating local weak points that reduce toughness and strength.

API 571 - API 571 Corrosion and Materials Practice Test

API 571 - API 571 Corrosion and Materials Practice Test

API 571 Mechanical and Metallurgical Failures 2