Effect of stress and surface finish on Pb-caustic SCC of alloy 690TT

• Published in: Corrosion science 2021-07, Vol.187, p.109462, Article 109462
• Main Authors: Mazzei, G.B., Burke, M.G., Horner, D.A., Scenini, F.
• Format: Article
• Language: English
• Subjects: Alkaline corrosion (C); Corrosion effects; Crack initiation; Crystallography; De-alloying (C); Fracture mechanics; Ni-base alloys (A); Nickel base alloys; Nucleation; STEM-EDX microanalysis (B); Stress analysis; Stress corrosion (C); Stress corrosion cracking; Superalloys; Surface finish; Surface preparation; TEM (B)
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2021.109462

[Display omitted] •The effect of stress and surface finish on caustic-PbSCC on Alloy 690 was studied using C-rings.•The threshold stress for cracking was identified in proximity of the yield point of the material.•A Cr-Fe spinel, which embedded in nodules of metallic Ni, formed on the surface deformed layer.•Crystallographic corrosion slots formed on the deformation-free surface.•A film-rupture/slip-dissolution mechanism assisted by de-alloying is proposed. The effect of surface preparation on lead-induced stress corrosion cracking (PbSCC) of Alloy 690 TT in Pb-caustic solution was investigated using C-rings manufactured from tubing that was either as-manufactured or polished. The surface deformed layer on the as-manufactured samples promoted the formation of an oxide, which reduced the number of sites for crack nucleation. Conversely, the polished surface developed crystallographic corrosion slots from which some of the cracks seemed to initiate. Advanced microstructural characterization complemented with stress analysis of the samples, suggested that the early stages of PbSCC are consistent with a film-rupture/slip-dissolution mechanism and influenced by de-alloying.