In high temperature corrosion, besides oxygen attack, alloys frequently encounter attack by carbon species. This attack can take two forms namely carburization and metal dusting (some times refereed to as catastrophic carburization). Carburization generally occurs at carbon activities <1 and at temperatures > 800 ° C and results in alloy embrittlement due to formation of internal carbides. Metal Dusting on the other hand leads to rapid wastage, thinning and disintegration of alloys into graphite and metal particles and occurs in environments with
carbon activities significantly greater than 1 and temperatures in lower range of 430 to 900 ° C. Metal dusting has been encountered in many industries such as in production of hydrogen, syngas, chemical plants for the synthesis of hydrocarbons, methanol, ammonia, in refineries, petrochemical plants, heat treating and reduction of iron ore plants. Attempts to inhibit metal dusting can take many forms such as using better alloy metallurgy, surface engineering modifications and/or pre-treatments of the alloy surfaces, use of coatings and using gas inhibitors such as addition of sulfide compounds (H2S), which causes other problems. This paper presents some laboratory data, field data and some applications of a new nickel base chromia-alumina forming alloy 602CA (UNS N06025) along with its physical metallurgy characteristics, in providing solutions to this mode of high temperature degradation.
Kevwords: Metal dusting, nickel alloys, alloy 602CA, UNS N06025, high temperature corrosion, carburization, chromia-alumina scale, syngas, ammonia synthesis, methanol production