If tape coating get disbonded from pipeline surface, an appropriate environment for corrosion can create under disbonded coating. Disbonded coatings are usually tape (Poly-ethylene) coatings and can disbond in different slope and morphologies. Despite extensive researches on corrosion under disbonded coating, there are no researches about effect of disbondment slope and morphology on corrosion under disbonded coating. Therfore in this study, the effects of disbondment morphology, slope and cathodic protection (CP) on electrochemical and corrosion of weld and base metal of pipeline steel under disbonded coating were investigated. Results shown, pH could decrease to acidic values due to increasing concentration of H + ions under disbondment region. An aggressive pitting corrosion could occur in mid region from open mouth (OM) of disbondment gap. Using no CP is better than using near OCP CP potentials. Because near OCP potentials can cause aggressive pitting corrosion at the end of disbondment gap. Corrosion rate of weld specimens were more than base metal specimens due to formation of galvanic cells on weld specimens. Decreasing disbondment gap size caused more aggressive pH drop but CP had less drop in lower gap sizes. Corrosion rate of steel decreased by decreasing gap size but in 1mm gap size an aggressive corrosion happened. Major products of pipeline corrsoion under disbonded coating are CaO in near OM region and FeHO 2 in bottom of disbondment gap.
