Material Degradation Analysis and Reliability Assessment of Residual Life for Service-Exposed Reformer Tubes
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JMEPEG https://doi.org/10.1007/s11665-020-05033-z
Material Degradation Analysis and Reliability Assessment of Residual Life for Service-Exposed Reformer Tubes Zhiyuan Han, Luowei Cao, LiKun Wang, Chenyang Du, Xiaolong Qian, and Guoshan Xie (Submitted August 31, 2019; in revised form July 2, 2020) 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. Keywords
material degradation, reformer tubes, residual life, Z-parameter
1. Introduction Reformer furnaces are widely used in a hydrogen plant to obtain hydrogen from hydrocarbon. The radiant coil tubes are the most critical components of a reformer furnace, which can be heated up to 850 °C or a higher temperature for long time during service. At present, HK (25% Cr, 20% Ni, 0.4% C) or HP grade (25% Cr, 35% Ni, 0.4% C) centrifugally cast austenitic stainless steels are selected as the tube materials for their high resistance to creep damage. According to the American Petroleum Institute (API) Recommended Practice 530, furnace tubes are generally designed for a nominal life of 100,000 h (Ref 1); but, sometimes, tube failure still happens before the designed life because of overheating or unexpected damage (Ref 2), which usually leads to unplanned shutdown of a plant and great losses (Ref 3). Thus, assessing the damage conditions and the residual life of furnace tubes is important. For an accurate life prediction of tubes, the current damage condition of a tube needs to be measured by either destructive or nondestructive methods. Then, tube life can be calculated by using an analytical model such as the Larson-Miller (L-M) method. Nondestructive examination methods usually include dimensional measurements, dye penetrants, radiography, ultrasonic inspections, and eddy currents. Several inspection
Zhiyuan Han, Luowei Cao, Chenyang Du, Xiaolong Qian, and Guoshan Xie, China Special Equipment Inspection and Research Institute, No. 2 Heping Street Chaoyang District, Beijing, Chin
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