Corrosion of Alloy 625 in aqueous solutions containing chloride and oxygen

Journal Article · Thu Oct 01 04:00:00 EDT 1998 · Corrosion

DOI:https://doi.org/10.5006/1.3284802· OSTI ID:669834

Kritzer, P; Boukis, N; Dinjus, E ^[1]

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1. Forschungszentrum Karlsruhe (Germany)

Alloy 625 (UNS N06625) is used frequently as a reactor material for the oxidation of hazardous organic wastes in supercritical water (supercritical water oxidation [SCWO]). In the presence of chloride (Cl{sup {minus}}) and oxygen (O{sub 2}), all Ni-based alloys corrode fast in high-temperature, subcritical water. High-pressure, high-temperature-resistant tube reactors made of alloy 625 were used as specimens. Coupons were exposed simultaneously inside the test tubes. Experimental conditions included temperatures up to 500 C and pressures up to 38 MPa. Pitting corrosion was observed at temperatures above {approx}130 C to 215 C. At higher temperatures (up to the critical temperature of water), transpassive dissolution dominated. Under certain conditions, transgranular stress corrosion cracking (TGSCC) appeared in the transition zone between the passive and transpassive regions leading to premature failure of the test reactors. Parts of the corrosion products were insoluble in supercritical water and formed thick layers in the supercritical part of the reactor. Underneath these layers, very little intergranular corrosion (IGC) occurred. In neutral or alkaline solutions and in deaerated hydrochloric acid (HCl), corrosion rates of transpassive dissolution decreased drastically.

• Sponsoring Organization: USDOE
• OSTI ID: 669834
• Journal Information: Corrosion, Journal Name: Corrosion Journal Issue: 10 Vol. 54; ISSN 0010-9312; ISSN CORRAK
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
HYDROCHLORIC ACID
INCONEL 625
INTERGRANULAR CORROSION
OXYGEN
PITTING CORROSION
PRESSURE DEPENDENCE
STRESS CORROSION
SUPERCRITICAL STATE
TEMPERATURE DEPENDENCE