Role of Iron in the Inhibition of Corrosion of Marine Heat Exchangers — A Review

Abstract

It was observed in 1907 that iron corrosion products in the cooling water of a marine condenser reduced tube corrosion. However, although intensive investigations in England reported in 1924 further emphasised the importance of iron corrosion products in reducing corrosion of copper base alloys, it is only very recently that the mechanism aspects of this role of iron have been reopened.

This review traces the history of the role of iron corrosion products as a corrosion inhibitor with particular reference to (a) the presence of iron corrosion products in the cooling water derived from either sacrificial galvanic iron protector blocks or by injection of ferrous sulphate into the system; (b) iron corrosion products provided from iron incorporated as an alloying element in the tube or tube plate material, considering in particular copper–zinc, copper–nickel and aluminium–bronee alloys.

It is concluded that, although the actual mechanism of corrosion inhibition depends on the source of iron corrosion products (from either the cooling water or condenser material), in both instances the iron becomes incorporated in the corrosion films formed on the metal surfaces. This reduces the potential of the films so that they are no longer effectively cathodic to bare metal and therefore cannot contribute to local electrochemical corrosion cells.