Severe metal-wastage was experienced on AISI Type 347 (18Cr-8Ni-Nb) and AISI Type 310 (25Cr-20Ni) used in the construction of a gas generator in which methane was burned with oxygen to produce carbon monoxide and hydrogen for fuel synthesis of the Fischer-Tropsch type. The mode of attack varied with temperature. At the highest temperatures, above 1650 to 1800 F, it consisted of straight oxidation, progressing intergranularly. With decreasing temperatures, heavy carburization with occasional signs of interspersed oxidation manifested itself. As temperatures declined further, cycling carburization, oxidation and reduction were observed, accompanied by severe metal wastage.
Typically attacked metal surfaces consisted of a semi-scale containing tiny globules of metallic particles surrounded by carbon or graphite interspersed with oxide. Tests with specimens of numerous steels and alloys installed at various locations in the reactor showed that the most resistant materials were those which best resisted carburization, that is, nickel, Monel, Inconel, AISI Type 446 (27 chrome-iron), copper, and pack-calorized materials. 4.2.3
