Corrosion of alloy 625 in high-temperature, high-pressure sulfate solutions

Journal Article · Tue Sep 01 04:00:00 EDT 1998 · Corrosion

DOI:https://doi.org/10.5006/1.3284888· OSTI ID:669782

Kritzer, P; Boukis, N; Dinjus, E ^[1]

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1. Forschungszentrum Karlsruhe (Germany). ITC

Corrosion phenomena of alloy 625 (UNS NO6625) were investigated in oxygenated aqueous solutions containing sulfuric acid (H{sub 2}SO{sub 4}), sodium hydrogen sulfate (NaHSO{sub 4}), or sodium sulfate (Na{sub 2}SO{sub 4}) and in deaerated H{sub 2}SO{sub 4} solution. Tests were conducted at temperatures and pressures up to 500 C and 38 MPa, respectively. Corrosion in the oxygenated acidic solution started {approximately}150 C with intergranular attack (IGA). Above 250 C, the whole surface of the alloy was attacked, and shallow pits and deep IGA appeared. This behavior was explained by transpassive dissolution of the protecting Cr(III) oxide layer. Severe material loss occurred between 300 C and 390 C. At higher temperatures, only weak corrosion was detected probably because of the lower density of the solution. Corrosion phenomena in oxygenated NaHSO{sub 4} solution were comparable but less severe than in H{sub 2}SO{sub 4}. In oxygenated Na{sub 2}SO{sub 4} solutions, no corrosion was observed up to the maximum test temperature of 350 C. In oxygen-free solutions, severe material loss occurred between 135 C and 220 C. The cathodic reaction was the reduction of sulfate, and the resulting potential was in the active region of the alloy. Above 230 C, the alloy passivated, and corrosion rates were low.

• Sponsoring Organization: USDOE
• OSTI ID: 669782
• Journal Information: Corrosion, Journal Name: Corrosion Journal Issue: 9 Vol. 54; ISSN 0010-9312; ISSN CORRAK
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CORROSION
DISSOLUTION
HIGH PRESSURE
INCONEL 625
OXYGEN
SULFATES
SULFURIC ACID
TEMPERATURE RANGE 0400-1000 K