Effect of ammonium chloride on corrosion behavior of Ni-based alloys and stainless steel in supercritical water gasification process

The corrosion behavior of 316 SS and three Ni-based alloys 625, 600 and 800 was evaluated by exposing in SCW at 400 °C and 24 MPa with 6000 ppm NH₄Cl for 70 h. Various of analytical techniques were used for corrosion analysis. 316 SS underwent severe corrosion attack for general corrosion, pitting corrosion and intergranular attack. Inconel 625 showed the best corrosion resistance in the test environment. Fe oxides and spinel were identified by XRD on all of the SCW-exposed samples. Trace amounts of NiO was also identified on the surface of samples, however, Ni was selectively dissolved and depleted in oxide films, and nickel ammine may form at the relatively low temperature during the heating and cooling process.