Type 304 Stainless Steel in Sulfuric Acid

Corrosion of Type 304 Stainless Steel in Sulfuric Acid 

Type 304 stainless steel is basically an alloy of 18 to 19 wt% Cr and 8 to 10 wt% Ni. Its corrosion behavior in sulfuric acid is sensitive to both alloy composition and the sulfuric acid environment. Variables with respect to alloy composition include whether the Cr and Ni concentrations are high or low within the allowed range and the concentrations of residual elements such as sulfur, phosphorus, copper, and molybdenum. Thermal and mechanical treatments are also variables but are not considered in the following. Important variables with respect to the sulfuric acid environment include degree of aeration and agitation (velocity effect) and small concentrations of species such as nitric acid, cupric ions, and ferric ions. The net influence of these variables is to find corrosion rates varying from 25 pm/year (1 mpy) to 2500 pm/year (100 mpy) (Ref 3 9). 

Fig- 5.43 Schematic polarization curves for type 304 stainless steel in 1 N H2S04. L (low) and H (high) distinguish the effects that minor composition variables can have on the position of the active peak current density (icrit) in the stainless steel polarization curve. 

The result is a corrosion rate of about 10 mA/m2, icorr (L). In contrast, the alloy with the higher anodic peak would not be passivated. The polarization curves cross in the active potential range of the alloy resulting in an active corrosion rate corresponding to about 250 mA/m2. 

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