This paper highlights the assessment of creep damage of 11 years service-exposed reformer tube made up of HP-40 grade of steel of a petrochemical industry from replicated creep data. The existence of scatter in the void characterization, creep deformation and rupture data leads to substantial amount of uncertainty in the assessment of creep damage. A discontinuous Markov process, which takes into account the associated scatter observed in damage evolution, has been used for creep damage assessment. The damage parameter A* is compared with the damage prediction by Markov process, where A* is derived as the cumulative contribution from microstructurally determined cavities at grain boundaries (A1) as well as number of creep cavities or voids at the grain boundary triple points (A2). This damage parameter (creep cavitation/voids) is in close agreement with the damage prediction curves at low stress where as at high stresses it could correlate well till the mid region of the predicted curves, above which cavity measurement was practically not feasible. Also the value of damage tolerance parameter λ (ratio of rupture strain to Monkman–Grant constant) infers that growth of cavities has been attributed to a purely diffusion controlled mechanism, grain boundary sliding mechanism or a combination of two.
