Abstract
Sulfuric acid is one the most common chemicals used and handled within the process industries. Applications range from leaching to industrial polymer production to pharmaceuticals manufacture. The range of concentrations extends from the very dilute to the viscous oil-like concentrated acid and this results in a range of corrosion issues. Sulfuric acid can show reducing behavior at low concentrations and have a higher redox-potential with oscillating behavior at high concentrations. This clearly presents challenges to the materials specifier. The corrosion resistance varies with concentration and temperature, with its most aggressive condition at the mid-range concentrations.
In this paper, the performance of a number of stainless steel grades in sulfuric acid have been thoroughly investigated in a series of laboratory tests, including evaluation of parameters such as the effect of activation, which may be necessary to simulate the effect of damage to a stainless steel surface, and chlorides, which can drastically increase the corrosion rate. Using activation of the specimens is shown to give higher corrosion rates and thus provide a more conservative basis for materials selection. Long term tests may also give lower corrosion rates because of a decrease in corrosion rate with time.
Results show that the measured corrosion rates were strongly influenced by the actual test procedure employed, and the different stainless steels cannot be properly compared unless the tests have been carried out with a rigorous control of the methodology. A critical comparison between the two superduplex grades UNS S32750 and S32760 showed no significant difference between the two, in any of the conditions in which it is reasonable to use these grades, when identical methods were used.
