Expert ForumsCorrosion

Topic: Re: Selecting Materials of Construction For Sulfuric Acid Service

posed by 
It is unwise to select materials of construction for equipment that will handle sulfuric acid based only on published corrosion data. The corrosion of metals by sulfuric acid is complex and small differences in impurities, velocities, and concentration can significantly impact corrosion rates. Therefore, general corrosion data should only be used as an indicator of relative corrosion resistance and as a guide for further review. The classic metal alloy for sulfuric acid service is Alloy 20 (20% Cr, 29% Ni, 3% Cu, and 2% Mo) and its derivatives. Newer superaustenitic stainless steels like 254SMO and AL6XN can also be used and have improved resistance to chloride impurities. Most non-fluorinated thermoplastics can be used for sulfuric acid service up to 80 °C and 25% concentration. Fluorinated plastics can also be used and have higher temperature limits than the non-fluorinated plastics. Both non-fluorinated and fluorinated plastics are used as liners. Lead can be used as a lining material at these temperatures and concentrations. However, it has fallen into disuse because of poor mechanical properties, lack of skilled craftsmen, and health and toxicity concerns. FRP can be used as the reinforcing structural element with a thermoplastic liner in dual-laminate construction. The corrosion resistance depends primarily on the resistance of the liner although resistant resins are often recommended in case of permeation and leaks in the liner material. There are many good publications available on selecting materials of construction for sulfuric acid service ("MS-1 Material Selector for Hazardous Chemicals - Sulfuric Acid" published by MTI) and I suggest you consult these for further, more detailed information.