1. What are the characteristics of ductile rupture?
Significant plastic deformation before failure. Reduction in cross-sectional area. Cup-and-cone fracture appearance. Typically from short-term overpressure. Material operated above yield strength.
2. How does brittle fracture manifest in boiler tubes?
Little or no plastic deformation. Flat fracture surface appearance. Often originates at stress concentrators. Can occur at stresses below yield. More common in older or degraded materials.
3. What causes stress rupture failures?
Long-term exposure to high stresses at temperature. Progressive creep damage accumulation. Final rupture after significant deformation. Microstructural changes evident. Common in superheater applications.
4. How does thermal fatigue damage develop?
Cyclic thermal stresses from startups/shutdowns. Crack initiation at high-stress areas. Progressive crack growth with cycles. Often shows multiple parallel cracks. Affects thick-section components most.
5. What are the signs of corrosion fatigue?
Combination of cyclic stress and corrosive environment. Crack surfaces show corrosion products. Typically transgranular crack path. Multiple origins common. Reduced fatigue life compared to air.
