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