Stress corrosion cracking initiation under the disbonded coating of pipeline steel in near-neutral pH environment

A novel test setup has been used in this study to simulate stress corrosion cracking initiation under a disbonded coating on an X-65 pipeline steel. In this setup, the synergistic effects of cyclic loading, cathodic protection and soil solution environment under disbonded coatings have been considered. When the X-65 pipeline steel was exposed to the test environment, there existed a wide range of corrosion products on the steel surface in the gradient of cathodic protection. Increasing the test time and the maximum stress increased the possibility of stress corrosion cracking initiation in regions with a high susceptibility to pitting corrosion.

Research highlights
► There could be a wide range of corrosion products on the steel surface in the gradient of cathodic protection under the disbonded coating.
► CP could effectively mitigate the pitting corrosion under the disbonded coating at regions with sufficient CP.
► Pitting corrosion under the disbonded coating is most severe at regions with insufficient CP; not regions completely free from CP.
► Micro cracks could initiate both from the surface and bottom of pits.
► Stress, time, and the level of CP are the three important factors in increasing the possibility of near-neutral pH SCC initiation.