API 571 Mechanical and Metallurgical Failures

Question 1

Fatigue crack initiation preferentially occurs at which locations in process equipment?

Accepted Answer

At stress concentrations such as notches, surface defects, or sharp geometry changes

Answer

At the center of solid cross-sections

Answer

At locations of maximum compressive stress

Answer

Only in the heat-affected zones of welds

Question 2

Which characteristic feature is found on fatigue fracture surfaces that distinguishes them from other failure modes?

Accepted Answer

Beach marks or clamshell patterns showing crack progression

Answer

Shear lips and ductile dimples throughout

Answer

Cleavage facets indicating brittle fracture

Answer

Intergranular fissures parallel to the surface

Question 3

Brittle fracture in carbon steel is most likely to occur under what temperature condition?

Accepted Answer

At or below the ductile-to-brittle transition temperature (DBTT)

Answer

At high temperatures above 300°F where steel is ductile

Answer

At any temperature under very slow loading rates

Answer

Only in austenitic materials at cryogenic temperatures

Question 4

A fatigue fracture surface characteristically shows which combination of features?

Accepted Answer

A crack growth zone with progression marks and a final rapid fracture zone

Answer

Uniform gradual wall thinning across the section

Answer

Uniform plastic elongation before fracture

Answer

Pitting and corrosion products on the fracture face

Question 5

Thermal shock in process equipment is caused by which mechanism?

Accepted Answer

Rapid, extreme temperature changes creating severe thermal gradients that exceed material limits

Answer

Sustained uniform high-temperature operation

Answer

Radiant heat exposure from nearby fired equipment

Answer

Creep deformation at sustained high temperature

Question 6

How is low-cycle fatigue distinguished from high-cycle fatigue?

Accepted Answer

Low-cycle fatigue involves fewer than approximately 10,000 cycles with high strain amplitudes

Answer

Low-cycle fatigue occurs at higher frequencies than high-cycle

Answer

Low-cycle fatigue only affects high-alloy materials

Answer

Low-cycle fatigue requires temperatures above 500°F