Corrosion characteristics of X70 pipeline steel under disbonded coatings in Kuerle soil environment

The chemical characteristics of trapped liquid and the corrosion features of X70 pipeline steel under a disbonded coating in a simulated solution of Kuerle soil were studied by using the rectangular stripping gap model. With the increasing of test time, the pH value of trapped solution gradually declines and finally reaches a stable level. Cl^- has different degrees of gathering and its highest concentration occurs in the end of the gap. The concentration of SO₄^2- decreases at the initial stage but increases at the late stage, the concentrations of HCO₃^- and NO₃^- decrease slightly from the holiday to the end, and the concentration change of cations is not obvious or only a minor reduction. The corrosion morphology of X70 steel under the disbonded coating performs obvious pitting corrosion, which is much more serious with the increasing of distance from the holiday.