Corrosion of Ferrous Materials by Deaerated Hot Fresh Water in a Desalting Plant

Abstract

Deaerated hot fresh-water produced by a multi-flush evaporator has much corrosive effect on ferrous materials used for the evaporator. To examine the effect of some environmental factors of the fresh-water on the corrosion of ferrous materials, autoclave tests were conducted. In this study, mild steel and 2 1/4 Cr-1 Mo steel were used as test samples and exposed to the fresh-water of various dissolved oxygen levels, chloride ion contents, and temperatures. The results obtained from this study were as follows.
Speaking in general, both the corrosion losses and the effects of the environmental conditions were small under static condition. Under a dynamic condition (flow rate 2m/sec), however, the corrosion losses indicated a remarkable increase, and at the same time, the effect of each environmental condition became clear. In all the test conditions, the corrosion resistance of 2 1/4 Cr-1 Mosteel was proved to be superior to mild steel. The corrosion rate of mild steel in the fresh-water at a high flow rate was larger than expected, and it was as large as twice than that in 3% sodium chloride solution according to conditions. These unusual results were assumed to depend on the instability of some oxide film (it may be magnetite) formed in the fresh-water.