Alloy T21 (UNS N06210), which comprises 19% chromium, 19% molybdenum, 1.8% tantalum, and the remaining composition of nickel, shows excellent corrosion resistance against pitting and crevice corrosion attack as compared to other commercial Ni-Cr-Mo alloys such as alloys C-276, 22, 59, and 686. Alloy T21 has a high pitting resistance equivalent (PRE) number, which is calculated from the compositions of chromium and molybdenum: this alloy exhibits excellent localized corrosion resistance, which exceeds its PRE number. The addition of a small amount of tantalum to an experimental Ni-Cr-Mo alloy has remarkably improved its corrosion resistance against pitting and crevice corrosion attack. Furthermore, a butt weld of alloy T21 also exhibits excellent pitting resistance as compared to those of other commercial Ni-Cr-Mo alloys. Butt welds of experimental Ni-Cr-Mo alloys that contain tantalum show superior pitting resistance as compared to those of Ni-Cr-Mo alloys that do not contain tantalum. The beneficial effects of tantalum are in a way that it improves the localized corrosion resistance of Ni-Cr-Mo alloys and the welds produced using the alloys.

Subject
Tantalum, Corrosion resistant alloys, Composition, Pitting temperature, Nickel based alloys, Molybdenum alloys, Nickel chromium molybdenum alloys, Commercial alloys, Green death, Corrosion attacks, Crevice corrosion, Pitting, Corrosion resistance
Keywords:
Ni-Cr-Mo alloy, UNS N06210, PRE, corrosion resistance, localized corrosion resistance, pitting, crevice corrosion, tantalum, Green Death solution
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2008
Association for Materials Protection and Performance (AMPP)
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