The Corrosion Potential of Welded and Thermally Aged Alloy 22 in Aerated Aqueous Solutions

Alloy 22 (N06022) is a nickel base alloy highly resistant to all forms of corrosion.  In aggressive environmental conditions Alloy 22 could suffer localized attack such as crevice corrosion.  For a given application, the occurrence of localized corrosion is governed by the values of the critical potential (E_crit) for crevice corrosion and the corrosion potential (E_corr).  If by natural evolution E_corr may reach potential values in the order of E_crit, localized corrosion may be expected. (In many environments Alloy 22 does not undergo crevice corrosion since the conditions for the attack cannot be established regardless the value or E_corr). The objective of this work was to study the metallurgical effect of Alloy 22 on the corrosion potential in a variety of electrolyte solutions. The E_corr of Alloy 22 was monitored as a function of time for non-welded (or mill annealed – MA), as-welded (ASW), and as-welded plus high temperature aged (HTA) rods. The six different electrolyte solutions studied included acidic and alkaline, reducing and oxidizing, detrimental and non-detrimental for crevice corrosion. In general the HTA rod established the highest E_corr followed by the ASW and the MA rods.