In-Service Evaluation of Alumina-Forming Alloy Tubes Extracted From Ethylene Cracking Coils

In high-temperature petrochemical processes such as ethylene cracking, furnace coil materials operate under extreme thermal and chemical stresses, leading to oxidation, carburization, and mechanical degradation. Developing advanced alloys with superior surface oxide stability and microstructural resilience is essential for ensuring reliability and extending component life. Paralloy Group specialises in centrifugal casting of high-nickel and high-chromium refractory steel tubes designed for severe high-temperature and corrosive environments. Among these, the proprietary alumina-forming alloy, XAl4 has been engineered to enhance oxidation resistance through the formation of a stable, adherent alumina (Al₂O₃) protective layer.

Our study investigates the performance of XAl4 tubes extracted from an ethylene cracking furnace after extended service at temperatures exceeding 1000 °C. A comprehensive, multi-technique evaluation was conducted to assess mechanical integrity, microstructural evolution, and surface degradation across different coil sections. Results confirm that the alumina layer on XAl4 remained continuous, and adherent throughout service, providing excellent resistance to oxidation and carburization. Minimal spallation occurred even in the most thermally exposed regions, validating the protective stability of the Al₂O₃ layer. Microstructural observations revealed a stable austenitic matrix with limited carbide coarsening, indicating robust metallurgical stability under prolonged exposure. Mechanical tests showed XAl4 retained a significant portion of its initial tensile and creep strength, with variations correlated to local operating conditions.

Overall, these findings demonstrate the high-temperature durability of XAl4 and highlight the effectiveness of alumina-forming alloys for next-generation furnace applications. This work offers critical insights for lifecycle assessment, maintenance strategies, and alloy optimisation, emphasising the importance of location-specific evaluation in post-service characterisation.

Nagesh Narasimha Prasad 1, Kevin Dourgaparsad 1, Abel Rapetti 1, Begoña Gomez Ferrer 1, Naveen Manikanteswaran 2, Dominique Flahaut 2

1 Manoir France SAS, 12 Rue des Ardennes, 27590 Pîtres

2 Paralloy Ltd, Paralloy House, Nuffield Road, Billingham, TS23 4DA