Deducing Crack History in an Aged Boiler Tube from Fracture Surface Topography

Abstract A new fractographic technique, FRActure Surface Topography Analysis (FRASTA), was applied to a crack in a boiler tube of a fossil-fired power plant in an attempt to determine when in its 22-year service history the crack initiated and the rate at which it grew. By comparing the topographies of the conjugate crack surfaces, we estimated that the crack nucleated about 68 000 h after onset of service and experienced several periods of accelerated and decelerated growth with rates ranging from 5 × 10 to 9.5 × 10 mm/h. These findings correlated roughly with chemical cleanings and startup/shutdown cycles. A similar analysis of a corrosion fatigue specimen tested under controlled conditions in the laboratory provided results consistent with measured values. These results suggest that fractography can be used to extract valuable information on cracking kinetics in aged systems and thereby, lead to new ways to predict, monitor, and extend component life.