Corrosion-creep interaction of stainless alloys in acid chloride solutions

Abstract

Rupture of passive film is considered as an essential step in the stress corrosion cracking (SCC) process. At constant load, accumulation of creep strain is often associated with the strain to passive film rupture. Therefore, low-temperature creep behavior of a material is important from an SCC point of view. Constant load creep studies carried out on alloy 22 (a Ni-22Cr-13Mo-4W alloy) in acidified chloride environments at 80 °C showed a logarithmic creep behavior. The creep strain decayed logarithmically and reached values less than 4 ϫ 10 Ϫ9 /s, which is lower than the detectable limit of laboratory scale SCC tests. 304 SS showed SCC failure in acidified chloride solutions in simulated open circuit conditions. A steady-state creep strain rate could be observed during SCC failures, of the order of 10 Ϫ5 to 10 Ϫ6 /s. The high creep strain rate of 304 SS can be correlated to the observed higher corrosion currents, which were more than 40 times that observed in alloy 22. When the dissolution rate of alloy 22 was increased by impressing about 1 mA/cm 2 anodic current, a steady-state creep strain rate of 6.5 ϫ 10 Ϫ8 /s was observed. The results indicated that anodic dissolution increased the localized plasticity of the material, resulting in creep strain. However, alloy 22 did not show SCC.

Characterization of surface composition on Alloy 22 in neutral chloride solutions

“…The XPS results clearly demonstrate the loss of Cr 2 O 3 for potentials > 0.2 V, which would explain the decrease in resistance observed in previous EIS studies over this potential range (1). [23] The increase in film capacitance which accompanies oxidation in the transpassive region (2) [23] can then be attributed to the 3 . This suggests that destruction of the Cr(III) oxide barrier layer leads to the transport of Cr(III) to the outer regions of the film.…”

“…These alloys are widely used in a range of industrial applications, [1] and Alloy 22 was recently considered as the corrosion barrier on packages for the permanent disposal of nuclear wastes. [2] This last potential application stimulated many studies on this alloy and, to a lesser degree, other Ni-Cr-Mo alloys, on processes such as intergranular corrosion, [3,4] localized corrosion with an emphasis on crevice corrosion, stress corrosion cracking, [26][27][28][29] and general passive corrosion. [9,[30][31][32][33][34][35] Alloy 22 develops a very stable passive film [27,[36][37][38][39] whose electrical properties have been characterized by electrochemical impedance spectroscopy (EIS).…”

“…These alloys are widely used in a range of industrial applications, and Alloy 22 was recently considered as the corrosion barrier on packages for the permanent disposal of nuclear wastes . This last potential application stimulated many studies on this alloy and, to a lesser degree, other Ni‐Cr‐Mo alloys, on processes such as intergranular corrosion, localized corrosion with an emphasis on crevice corrosion, stress corrosion cracking, and general passive corrosion …”

The Influence of Potential and Temperature on the Kinetics of Oxygen Reduction on Alloy 22 in Neutral Chloride Solutions.

“…However, seepage water contacting the waste package could evaporatively concentrate to produce a concentrated, corrosive environment (5)(6)(7)(8) potentially leading to crevice corrosion over the required long-term containment period. With this application in mind, intergranular corrosion (9,10), localized corrosion (5,(11)(12)(13)(14)(15)(16), stress corrosion cracking (17)(18)(19)(20), and general passive corrosion studies have been undertaken (21)(22)(23)(24)(25)(26)(27)(28). In addition, surface analytical studies have been performed, including X-Ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectroscopy (ToF SIMS) (24,29), Atomic Force Microscopy (AFM) (28,30), and Electron Backscatter Diffraction (EBSD) (28).…”