Stress corrosion of pipeline steel under occluded coating disbondment in a red soil environment

• A crevice cell with a loading frame was constructed to study SCC of pipeline steel.
• Severe corrosion attack and microcrack initiation is preferential at the holiday.
• Species gradient and internal polarization enhance corrosion at the holiday.
• Yield stress applied remarkably enhances corrosion and microcrack at the holiday.
• Thin occluded shielding gap restricts CO2 access under disbonded coating.

A crevice cell with a multi-sample loading frame was constructed to study stress corrosion initiation of pipeline steel under an occluded shielding plate simulating coating disbondment under free corrosion condition in a red soil environment. The local potential and pH under the shielding were monitored by microelectrodes. Results show that intensive anodic dissolution and initiation of microcrack were preferential at the open holiday, whereas the corrosion attack was markedly mitigated under the occluded shielding. Species gradient and internal polarization were proposed for the corrosion scenarios of pipeline steel under disbonded coating.