Corrosion can also occur in condensate return lines. Corrosion can be caused by oxygen in the steam or carbon dioxide which leads to the production of carbonic acid. Oxygen should ideally have been dealt with by the treatment of the feed water but any remaining can be removed using steam volatile oxygen scavengers. Carbon dioxide corrosion can be controlled by pre-treatment techniques or by the addition of steam volatile neutralising and filming amines. Filming amines are generally dosed into the steam lines and form a protective film on the surface of the condensate lines. Neutralising amines enter the condensate lines with the steam and neutralise the carbonic acid thereby raising the pH.