Long-Term Corrosion Behavior of Alloy 22 in 5 M CaCl₂ at 120°C

In conditions where tight crevices exist in hot chloride containing solutions Alloy 22 may suffer crevice corrosion. The occurrence (or not) of crevice corrosion in a given environment (e.g. salt concentration and temperature), is governed by the values of the critical potential (E_crit) for crevice corrosion and the corrosion potential (E_corr). This paper discusses the evolution of E_corr and corrosion rate (CR) of creviced Alloy 22 specimens in 5 M calcium chloride (CaCl₂) at 120°C. Tested specimens included non-creviced rods and multiple creviced assemblies (MCA) both non-welded (wrought) and welded. Results show that Alloy 22 suffers crevice corrosion under the open circuit conditions in the aerated hot CaCl₂ brine. However, after more than a year immersion the propagation of crevice corrosion was not significant. The general corrosion rate decreased or remained unchanged as the immersion time increased. For rods and MCA specimens, the corrosion rate was lower than 100 nm/year after more than a year immersion time.