The capability to perform very user-friendly, thermochemical analyses of complex, real alloys corroding in complex, high-temperature gases has been developed. Predictions of the stabilities of complex assemblies of corrosion products formed by reactions of alloys containing Fe-Cr-Ni-Co-C-N and gases containing S-C-O-H-N species can now be done with unprecedented accuracy and generality. The thermochemical data models are based upon extensive analyses of all available thermochemical data for all possible solid and liquid compounds and solutions based upon all combinations of Fe-Cr-Ni-Co-S-CO- N and for all possible gaseous species containing S-C-O-H-N. As well, the alloying elements Al, Mo, Nb, Ti, V, W, Mn and Si are fully included in the alloy and carbonitride solution models. Comprehensive and accurate solution models are used to assess the interactions of multiple species interactions in variable composition solid and liquid phase alloys, sulfides, oxides, carbides, and nitrides. This capability is used to predict the stable corrosion products, which are useful in inferring the dominant corrosion mechanism, in complex conditions.
BACKGROUND
This paper discusses an effort to create a software facility1 to predict the stabilities of corrosion products of commercial alloys, which might form in complex, real industrial gaseous environments. Hightemperature gases can corrode metals by many different mechanisms for a wide range of conditions. Corrosion by hot gases is possible in process equipment such as: petroleum refineries, gas processes, fired equipment, process heaters, burners, flares, furnaces, boilers, thermocouples, instrumentation, hydrocracking, coking, vacuum flashers, hydrotreaters, coal/coke/oil gasifiers, petrochemical production, catalytic reformers, waste incineration, hydrogen plants, heat treatment ovens, ammonia production, power generation, electric heaters, and many other examples.
The ability to predict and then manage corrosion of alloys in high-temperature corrosive gases in many processes often depends upon knowing the type of corrosion, which might occur.2 However, an important obstacle to predicting corrosion has been the variety of the combinations of alloys and corrosive environments. Therefore, this project has compiled and analyzed all available thermochemical data for all known solid and liquid compounds and solutions which can form from all possible combinations of Fe- Cr-Ni-Co-S-C-O-N and for all possible gaseous species containing S-C-O-H-N. As well, the carbide and nitride forming alloying elements Al, Mo, Nb, Ti, V and W, together with the alloying elements Mn and Si, are fully included in the alloy and carbonitride solution models, while the oxides and sulfides of these elements are treated as pure stoichiometric compounds. The CRCT3 in École Polytechnique de Montréal, Canada led by Prof. A. D. Pelton is leading the effort in this data analysis. The technology considers solids, liquids and gases of both fixed and variable compositions to predict the phase stabilities. The phase predictions have been compared to known/measured phase diagrams and the predictions are able to reproduce the phase diagrams, within the ability to measure the diagrams. Many aspects of equipment/process design, process operation, alloy selection, alloy design, and plant maintenance are influenced by the expected lifetimes of equipment in high-temperature, corrosive gases, which can often be determined by the types of corrosion products which form. Process equipment typically has maximum allowable temperatures, or other process conditions, which are limited by the types of corrosion expected for the equipment. Corrosion in high-temperature gases is affected by parameters of t
