The mechanism of stress corrosion cracking of Alloy 690TT in a caustic solution containing lead

• Published in: Corrosion science Vol. 128; pp. 154 - 163
• Main Authors: Hou, Qiang, Liu, Zhiyong, Li, Chengtao, Li, Xiaogang
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.11.2017; Elsevier BV
• Subjects: A. Nickel alloy; Alloys; B. TEM; C. Internal oxidation; Corrosion mechanisms; Crack propagation; D. Pitting corrosion; E. Stress corrosion; Grain boundaries; Lead; Microcracks; Oxidation; Oxides; Stress corrosion cracking; D. Pitting corrosion; A. Nickel alloy; E. Stress corrosion; B. TEM; C. Internal oxidation
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2017.09.015

•Pb-doped oxide films are similar, regardless of a surface or a crack tip.•Pb is evenly distributed in oxides and inhibits the formation of protective films.•Adding Pb, the pitting resistance deteriorates and GBs are severely oxidized.•The pitting can lead to the nucleation of a SCC crack under high stress condition.•Microcracks nucleate in GB oxides and link with a crack, causing SCC extension. This study investigated the PbSCC of Alloy 690TT exposed to a caustic solution at 320°C. Characterization of the resulting films indicates that lead is involved in the formation of oxides and evenly distributed in the films. TEM analysis was carried out to elucidate the role of lead in IGSCC by investigating the oxides at the crack tip. Lead penetrates into the crack tip and disperses in the intergranular oxides, enhancing the oxidation of grain boundaries. Thus, microcracks initiate within oxides under stress and connect with the main SCC crack stemming from the pit, resulting in propagation of the IGSCC.