Application of double loop electrochemical potentiodynamic reactivation test to austenitic and duplex stainless steels

Double loop electrochemical potentiodynamic reactivation (DLEPR) tests are performed on an austenitic (317L) and an austeno-ferritic (UNS S31803) stainless steels. In order to optimise results, the standard electrochemical solution has been modified by adding NaCl to the composition and by increasing the concentration of H₂SO₄. Results show a high resistance to intergranular corrosion of the 317L heat treated at 675°C for 30 min to 24 h. On contrast, the duplex stainless steel corrosion resistance decreases with time of sensitisation. Low exposure time (1 h at 675°C) provides low reactivation current density whereas longer exposure time (10 h) shows an increase in the value of this reactivation current, which is due to the formation of chromium carbides and sigma phase at grain boundaries leading to more chromium depleted areas. Heat treatment at 900°C shows a high reactivation proportional to σ-phase precipitation. The aim of this work is to validate the DLEPR technique for detecting susceptibility to intergranular corrosion of duplex stainless steels. This test is not yet normalised and could be used for on-site measurement.