The oxide film was locally broken in the places where a cuprite (Cu2O) layer was
formed, weakly adherent to the substrate. The possibility of an intermediate cuprite layer
forming between a tenorite (CuO) layer and copper metal was announced by the authors
of the works [1,9]. In the case of the examined tube, some shallow pits were created under
the malachite and cuprite layers. Chloride anions have no effect on SCC of copper [4] but
they are believed to be the main cause of pit initiation and propagation [15]. The latter
opinion is inconsistent with practical observations proving that nitrate content is important
to pitting [16].
Pits undoubtedly facilitating crack initiation by notching effect yielding to an increase
of stress at the pit bottom. Contribution of pits to SCC initiation can be of particular
importance in the cases where surface stresses in the tube are compressive stresses and tensile
rupture of tenorite film is impossible.