Hi Terry, sounds the same as my Emma Victoria I am building. The pipe is the steam pickup pipe, steam here is wet steam, on mine it then goes into the superheater and thence to the cylinders. I do not know if yours is a working engine or one in bits, if the latter note that the steam pickup pipe sits in a pressure retaining inner dome, the outer dome is the fancy bit you see and is just a cover. I assume most locos are very similar although I am not an expert, this is my first engine build.
Good luck.
Bill D.