Electrochemical noise characterization of heat-treated superduplex stainless steel

Three microstructures of superduplex stainless steel UNS S32750 were evaluated in which concerns their corrosion resistance in a 70,000 ppm chloride medium at 25 and 60 °C. These environmental conditions are found in ultra-deep offshore oil exploitation. The microstructures are related to as-received, as-welded and hot-worked steel processing. The corrosion behavior was characterized for 30 min and 24 h by means of polarization curves and mainly electrochemical noise, EN, measurements performed with a zero resistance ammeter setup. The results show that, in this highly aggressive environment, time and temperature affect the corrosion resistance of each microstructure differently. The presence of sigma precipitates at grain boundaries trigger the breakdown of passive films at lower potential as well as in the case of coupling different microstructures. The as-received homogeneous one is nonetheless also susceptible to undergoing corrosive attack at long-lasting high temperature exposition.