Investigation of the 0.4C-35Cr-45Ni-Nb Alloy after Service in High-Temperature Steam and Hydrocarbons Environment.

Juliusz Orlikowski,Michał Szociński,Kazimierz Darowicki,Janusz Zygmuntowicz,Gabriel Gajewski,Wojciech Filipkowski

doi:10.3390/ma14206139

Juliusz Orlikowski, Michał Szociński + Show 4 more

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https://doi.org/10.3390/ma14206139

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Abstract

The paper presents the results of investigation of the 0.4C-35Cr-45Ni-Nb alloy, which operated in the cracked hydrocarbon feeds and dilution steam at 1125 °C. The material originated from the pyrolytic furnace coil tubes, of which internal walls were in contact with the aforementioned medium, whereas the external walls were in contact with the flue gases. The examination included metallographic and mechanical tests on the material after service exposure, the results of which were compared with the ones obtained for the as-received non-exposed specimens. The metallographic tests revealed changes in the alloy’s structure manifested by formation of significant amount of the carbides due to carburization of the alloy from the steam and cracked hydrocarbon feeds side. The central and external parts of the alloy samples (having no contact with the process medium) underwent substantial degradation but within a relatively narrow zone of the material. The investigations of hydrogen and methane content in the alloy showed a high amount of these gases, resulting from high-temperature corrosion in steam environment. The mechanical tests demonstrated clear shortening of the plastic deformation range of the alloy due to penetration of the gases and formation of the carbides inside the material’s structure. A low level of corrosion and no creep mechanism were detected.

Highlights

The 0.4C-35Cr-45Ni-Nb alloy belongs to relatively new construction materials employed in the design of the furnaces operating at high temperatures in the petrochemical industry
The investigated alloy samples originated from the coil tubes of the pyrolytic furnace, where olefins are obtained from the cracked hydrocarbon feeds
External part, which was in contact with high temperatures and flue gases originating

Summary

Introduction

The 0.4C-35Cr-45Ni-Nb alloy belongs to relatively new construction materials employed in the design of the furnaces operating at high temperatures in the petrochemical industry. The alloy is characterized by high resistance to carburization and metal dusting in hydrocarbon environments [2]. It is applied typically in the petrochemical industry for construction of the furnaces as well as in the petroleum industry, mainly in reforming installations. The investigated alloy samples originated from the coil tubes of the pyrolytic furnace, where olefins are obtained from the cracked hydrocarbon feeds. The coal formed on the internal walls of the furnace’s coil tubes favors carburization and metal dusting processes due to high service temperatures [3]. Actual service conditions often differ from the ones predicted upon design, which contributes to high cost of premature replacement of the furnace’s parts [5]

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