Early corrosion properties of titanium alloys, Ni-based alloys and stainless steel in supercritical water oxidation of sewage sludge

Supercritical water oxidation (SCWO) can efficiently and harmlessly dispose sewage sludge, while corrosion phenomena can lead to rapid shutdown and/or failure of expensive process equipments in a supercritical water system. The corrosion behavior of titanium alloys, Ni-based alloys and stainless steel exposed in supercritical water oxidation of sewage sludge at 450 °C, 26 MPa for 60 h was investigated by means of gravimetry, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. 316 SS (stainless steel) showed the highest corrosion rate, while TA10 had the lowest corrosion rate. The oxide scale on the surface of 316 SS contained magnetite and FeCr2O4, while Cr2O3 and NiCr2O4 were the main components of oxide layer on Inconel 600. Among them, magnetite and NiCr2O4 mainly existed in the inner oxide layers of SS 316 and Inconel 600, respectively. The lack of Cr2O3 on the 316 SS surface resulted in severe pitting corrosion and poor corrosion resistance.