Material Degradation Analysis and Reliability Assessment of Residual Life for Service-Exposed Reformer Tubes

This study investigated the material degradation of service-exposed reformer tubes. Microstructural and mechanical experiments were carried out to reveal the property degradation, including optical and scanning electron microscope observations, room and high temperature tensile tests, and stress rupture tests. The rupture data were obtained, and the residual life was evaluated for tubes with different microstructures by both reliability-based Z -parameter method and deterministic method. The results showed the deterioration of microstructural and mechanical properties of the service-exposed reformer tubes. The material degradation was most critical for the overheated reformer tubes, and more serious in the lower part of tube than that in upper part. However, the difference in rupture data between upper and lower tubes was not significant. The results also demonstrated that the residual life evaluated by the Z -parameter method on confidence level of 99.9% was similar as that of the deterministic method by using average fit curves and maximum operating parameters, which was much less conservative than that evaluated by using 95% lower predication fit curves.