Nickel-based Alloy UNSa N07718 is used extensively in Oil & Gas upstream applications because of its high mechanical strength and good uniform corrosion resistance; however, in chloride environments N07718 can suffer localized attack, either due to pitting or crevice corrosion. An alternative to N07718 for Oil & Gas components is UNS N06625, which has a relatively better localized corrosion resistance compared to N07718 due to its higher pitting resistance equivalent number (PREN). A better option to both N07718 and N06625 is UNS N07022; which has high strength and excellent resistance to stress corrosion cracking, uniform and localized corrosion. The present study investigates the passivity and localized corrosion behavior of N07718, N06625 and N07022, in solution annealed and age-hardened conditions.

The critical pitting temperature (CPT) and critical crevice temperature (CCT) obtained for N07022 alloy, using ASTM G-48 guidelines, was significantly higher than that of N07718 and N06625. Electrochemical testing and immersion tests also showed a larger resistance of N07022 to localized corrosion compared to either N07718 or N06625. The higher resistance of N07022 is attributed to its higher content of both chromium and molybdenum (PREN).

Subject
Materials, Corrosion resistant alloys, Nickel based alloys, Molybdenum alloys, Sodium chloride, Crevices, Sodium chloride solution, Crevice corrosion, Acetic acid, Corrosion resistance, Localized corrosion, Alloys, Corrosion potential
Keywords:
UNS N07022, UNS N07718, UNS N06625, CPT, CCT, Localized Corrosion, Cyclic Potentiodynamic Polarization, Pitting Resistance Equivalent Number
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2015
Association for Materials Protection and Performance (AMPP)
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