The corrosion behavior of high-performance austenitic stainless steels and nickel-based alloys in hydrofluoric acid at room temperature was investigated. For alloys with Ni contents between 20 and 50% the corrosion rate can be described by general equations for aerated and deaerated hydrofluoric acid. The corrosion rate can be calculated considering the hydrofluoric acid concentration, the presence of air and the alloy content of Cr, Ni, Mo and Cu. These equations reflect a primary beneficial effect of Cr and Mo and a limited positive effect of Ni in aerated acid. In deaerated acid there is a primary beneficial effect of Ni, Mo and Cu and a limited positive effect of Cr. Thus the relative influence of the alloying elements can be described by an Alloy Equivalent Sum (AES) each for aerated and deaerated acid. The equations facilitate the selection of economic materials for HF-containing equipment at ambient temperature. Potentiostatic current density versus potential diagrams indicate if an alloy is active or passive at the respective corrosion potential and thus explain the different effect of aeration on corrosion (positive or negative) depending on alloy composition.

Subject
Acids, Iron nickel chromium alloys, Materials, Stainless alloys, Corrosion rate, Nickel based alloys, Molybdenum alloys, Nickel chromium molybdenum alloys, Copper alloys, Hydrofluoric acid, Copper nickel alloys, Alloys, Corrosion potential
Keywords:
Hydrofluoric acid, aerated, deaerated, corrosion, passivity, potentiostatic polarization, corrosion potentials, stainless steels, nickel alloys, Fe-Cr-Ni-Mo alloys
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2004
Association for Materials Protection and Performance (AMPP)
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