Structural integrity of service exposed primary reformer tube in a petrochemical industry

• Quantification of cumulative creep damage through microstructural studies.
• Scatter in voids are taken into account for damage assessment.
• Probability of failure at various true strain follows Weibull distribution.
• Estimation of mean time to reach a specific damage state agrees well with that of experimental data.

This paper aims at quantifying creep damage, in terms of Kachanav's continuum damage mechanics (CDM) model and Bogdanoff model of service exposed primary hydrogen reformer tube. Quantification of creep damage was made from scatter in voids which was quantified from light optical microscopy (LOM), SEM (scanning electron microscope) equipped with image analyzing technique and EDX analyser, in terms of two damage parameters A and A*. Scatter in creep deformation behaviour of the material, is probably due to variation in mode of fracture and scatter in voids. Probability of rupture due to void area, shifts towards the higher population of void with increase in true strain. Experimental data for estimating creep damage agrees well with both the simulation based models. The value of damage tolerance parameter λ infers that growth of cavities has been attributed to a purely diffusion controlled mechanism, grain boundary sliding mechanism, or a combination of both.