Does your question possibly have to do with the synthesis of urea formaldehyde? Regardless, I am not familiar with the chemistry you are asking about nor is this an area I have expertise in so I can only offer some general advice. The temperature is very hot and the chemicals you have mentioned, such as formic acid, can be quite corrosive especially at high concentrations. No doubt the impurities present in the raw materials and/or the by-products of the reaction chemistry will play a role in corrosivity. If this is a well-known manufacturing process there is likely a lot of information out there on specific MOCs for the unit operations involved. If not, you may be forced to run your own corrosion studies to determine alloys with acceptable performance. There is guidance in the literature and reference books that can help you do this. Good luck!