I have been using Autosol Bluing Remover followed by using ordinary metal polish for several years and the pipes are bright and shiny like new. However, it is less work doing it more often than once a year. The part of the pipes (5-10cm) close to the engine must be polished using sandpaper (first 600, then 1200) followed by sandingpaste using a Dremel. I assume that is related to pollution in the steel combined with the heat. Rather time-consuming. I enjoy spending time alone in the garage doing it... If you don't enjoy it, don´t do it - too time-consuming. But it is possible, and I have not experienced any damage.
