A 4" thick 5 chrome vessel operating at 1200 psig and 900°F is least likely to fail from Brittle Fracture during which condition?

A 4" thick 5 chrome vessel operating at 1200 psig and 900°F is least likely to fail from Brittle Fracture during which condition?

• A. During startup
• B. During normal operation
• C. During cooldown
• D. During rapid heating

Answer: (B)

Brittle fracture is least likely when the metal is in a stable, ductile state at high temperature with no large thermal gradients. At 900°F under steady high-pressure operation, a 5 chrome vessel has high toughness and behaves ductile, so cracks are unlikely to propagate. In contrast, cooldown or rapid heating introduce thermal gradients and transient stresses that can drive parts of the metal through the brittle regime or stress cracks, increasing fracture risk. Startup involves changing temperatures, which can also produce stresses, and rapid heating can cause thermal shock. Thus, normal operation, with steady high temperature and pressure, presents the lowest risk of brittle fracture.

Brittle fracture is least likely when the metal is in a stable, ductile state at high temperature with no large thermal gradients. At 900°F under steady high-pressure operation, a 5 chrome vessel has high toughness and behaves ductile, so cracks are unlikely to propagate. In contrast, cooldown or rapid heating introduce thermal gradients and transient stresses that can drive parts of the metal through the brittle regime or stress cracks, increasing fracture risk. Startup involves changing temperatures, which can also produce stresses, and rapid heating can cause thermal shock. Thus, normal operation, with steady high temperature and pressure, presents the lowest risk of brittle fracture.