Corrosion phenomena of alloy 625 pressure tubes were investigated in aqueous solutions containing up to 0.2 mol/kg sulfuric acid and up to 1.44 mol/kg oxygen. Applied maximum temperatures and pressures were 500 °C, and 38 MPa, respectively. Corrosion started at temperatures around 150 °C with intergranular attack. Above 250 °C, the whole surface of the alloy was attacked, shallow pits and deep intergranular attack appeared. This behavior can be explained by transpassive dissolution of the protecting Cr(III)oxide layer and leads to severe material loss. The upper temperature limit of severe corrosion at an experimental pressure of 24 MPa was about 390 °C. As temperature was increased further and the density of the solution dropped to low values, only slight corrosion was detected.

Subject
Pits, Transpassivation, Supercritical water, Water, Sulfuric acid, Tubes, Acid attack, Dissolution, Solubility, Density, Corrosion products, Metals, Oxygen
Keywords:
Corrosion, transpassive dissolution, intergranular attack, alloy 625, sulfuric acid, oxygen, high-temperature, high-pressure, supercritical water, SCWO
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1998
Association for Materials Protection and Performance (AMPP)
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