Alloy 625 is frequently used as reactor material for Supercritical Water Oxidation (SCWO) applications. TMs is due to the favorable combination of mechanical properties, corrosion resistance, price and availability. Nevertheless, the corrosion of alloy 625 like the corrosion of other
Ni-base alloys during oxidation of hazardous organic waste containing
chloride proceeds too fast and is a major problem in SCWO applications.
In these experiments high pressure, high-temperature resistant tube reactors made of alloy 625 were used as specimens. They were exposed to SCWO conditions, without organics, at temperatures up to 500 °C and pressures up to 37 MPa for up to 150 h. Simultaneously, coupons also made from alloy 625 are exposed inside the test tubes. The most importaut corrosion problem for alloy 625 is pitting and intercrystalliie corrosion at temperatures nenr the critical temperature, i.e. in the preheater and cooling sections of the test tubes. Under certain conditions, stress corrosion cracking appears and leads to premature failure of the test reactors. The corrosion products were insoluble in supercritical water and formed thick layers in the supercritical part of the reactor. Under these layers only minor corrosion occurred. Keywords: Alloy 625, corrosion, oxidation, SCWO, supercritical, water, oxygen, hydrochloric acid, high temperature, high pressure