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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2010

1 Łabanowski J.

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Evaluation of reformer tubes degradation after long term operation

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Łabanowski J.

Journal of Achievements in Materials and Manufacturing Engineering

2010

tom Vol. 43, nr 1

244-251

Purpose of this paper is to show the effect of long-term service at elevated temperatures on microstructural changes of cast steel reformer tubes made of the alloy IN-519 (24%Cr, 24%Ni, Nb). The relationship between mechanical properties and microstructure degradation is discussed. Design/methodology/approach: Investigations were performed on five tubes taken from ammonia reformer furnace. Tubes worked at temperature of 880şC and 3.2 MPa pressure. The operation time varied from 24000 to 95000 hours. Microstructure of the material has been examined with the use of light optical microscopy and scanning electron microscopy (SEM). The energy dispersive X-ray analysis (EDX) was used for phase identification. The mechanical properties have been evaluated in static tensile tests at room temperature. Findings: Metallographic investigations of IN-519 cast steel catalytic tubes show that structural changes occur in non-monotonic way with operating time at elevated temperatures. For this reason the evaluation of tube degradation can not be based only on the microstructure examinations. The presence of a good correlation between mechanical properties of the catalytic tubes and service conditions, i.e. temperature, time, and internal stress was confirmed. Research limitations/implications: The surface condition of the tubes walls like carburization and oxidation is not considered in this study. Practical implications: The method for assessing the current degradation level and for predicting residual lifetime of creep-resistant tubes has been established. The method uses elongation values as the main factor characterizing structural degradation of catalytic tubes. It respects all degradation mechanisms involved in tubes degradation, and can give reliable information on reformer tube condition through almost whole period of operation. Originality/value: Microstructure transformations occur in the IN-519 cast steel tubes during long-term operation in the reformer furnace were revealed and described