1. What is the temperature of your application?
H2SO4 behaves as you might expect with respect to temperature but it is a fairly sensitive variable. To put it simply, as temperature increases so does the corrosion rate but be cautious – the corrosion rate can increase rapidly with only small changes in temperature. So, temperature is usually more of a concern from a corrosion point of view than the usable temperature limits of the material since most H2SO4 environments are not above 200°C/400°F.
2. What is the concentration of H2SO4 ?
The corrosiveness of H2SO4 is highly dependent on the concentration. Logically, H2SO4 is less corrosive at a lower concentration and more corrosive at higher concentrations. This remains true when dealing with concentrations of 99% or less. For example, as you would expect a concentration of 97% H2SO4 is far more corrosive than that of 6%.
Yet, there is an exception to this rule when dealing with concentrations of 99% or greater. In such high concentrations, H2SO4 is not very corrosive at all. In fact, H2SO4 at these levels can be handled simply with carbon steel. So counter intuitively, a concentration of 99% is far less corrosive than a concentration of 98%.
However if your concentration is changing due to dilution this can be a bit tricky as well. Typically as you diluteacids they become less corrosive however in the case of sulfuricacid, as it is diluted it gives off heat (exothermic). Although dilution brings the concentration down, the temperature will increase (an increase in temperature heightens the corrosion rate: See Point 1) and therefore the solution could become more corrosive until the heat is removed.
3. What are your performance requirements and corrosion resistance expectations?
As for all fastener applications, it’s obviously important to consider the load and mechanical requirements of the application. Materials such as polymers, ceramics and metals could be used in H2SO4, so there is a range of material options that may be considered.
For more information about which material might be best for your H2SO4 environment
H2SO4 iso-corrosion curve comparing various high performance metals corrosion resistance. Each line represents a corrosion rate of 5 mils per year. The further the operating point is below the curve the better.