The use of duplex stainless steels as construction material for the chemical industry is today very widespread. The combination of high strength, high resistance to chloride environments and various acids makes this group of materials very interesting for equipment in the chemical industry, where high corrosion rates are observed for lower alloyed stainless steels such as AISI 304L and 316L. In the paper results from laboratory as well as in plant tests in organic acid environments are shown. In the laboratory tests the influence of chlorides, temperature, acid concentration and various contaminants has been investigated for acetic acid and formic acid. The results include corrosion rates and in some cases polarisation curves for the duplex stainless steels SAF 2205 and SAF 2507, and comparison has been made with austenitic stainless steels and Ni-base alloys. Some results from in plant tests in organic acid plants are also shown.

The results show that duplex stainless steels are very resistant to organic acids, also in presence of various contaminants, and also that their resistance in some cases is comparable to or even better than for high alloyed austenitic stainless steels and Ni-base alloys. The range of application in organic acids has been clearly determined, with well defined temperature and concentration ranges for the use of duplex stainless steels in various organic acids.