Coker furnace tube failures in delayed coking units at refineries can have a major impact on safety and reliability. Alloy 800HT (UNS N08811) coker furnace tubes experienced higher than expected corrosion rates at a few refineries in the United States. A metallurgical evaluation of the corroded coker furnace tubes indicated sulfidation corrosion to be the main operating damage mechanism. The presence of nickel in the alloy 800HT rendered it more susceptible to sulfidation, possibly due to formation of nickel sulfide eutectic phases that have low melting points. The sensitization of alloy 800HT during operation and maintenance activities also increased the susceptibility towards sulfidation. Other possible damage mechanisms, such as creep, naphthenic acid corrosion, and carburization were absent.

Subject
Corrosion rate, Microstructure, Nickel based alloys, Tubes, Chromium, Refineries, Furnaces, Oxide scales, Scale formation, Sulfidation, Nickel, Grain boundary, Alloys
Keywords:
Coker furnace tubes, alloy 800HT, sulfidation, sensitization, SEM
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2019
Association for Materials Protection and Performance (AMPP)
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