i have seen fittings of a type of steel silver soldered, or brazed, onto an aluminum condenser tube. the reason being, that steel and aluminum will corrode together, making removal of the threaded fitting impossible without destroying one, or both threaded fittings. we always chopped those off with bolt cutters before tossing them in the scrap pile. maybe your condenser was like that ? an iron condenser would weigh a ton [figuratively speaking], and i would think as thin as the tube mass is, would have cracking issues from vibrations that are always present. maybe export stuff was/is different than anything i have experience with ? or possibly, your condenser was a light weight steel tube design ? occasionally, we would run across one of those, but could immediately identify it based on just how heavy it "felt", as opposed to the "normal" aluminum condensers.