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

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.