Abstract

The material selection for nitric acid production is often based on iso-corrosion diagrams which are established by general corrosion testing in a laboratory environment. However, the critical parts in a nitric acid plant which suffer the heaviest corrosion are almost always exposed to alternating wet-dry zones. The condensation and evaporation circumstances give different corrosion mechanisms and other corrosion potentials than what is normal during general corrosion testing from which the iso-corrosion diagrams are established.

Electrochemical measurements were performed on two austenitic stainless steels UNS S30403 (304L) and S31002 as well as two austenitic-ferritic stainless steels UNS S32304 and S32906 which are known to be used as construction material in nitric acid plants. Special focus was put at the corrosion potential and the transpassive transition with the purpose to determine the corrosion resistance and transpassive potential for the steel grades. The influences of chemical composition and phase structure on the corrosion resistance are discussed in this paper.

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