The corrosion behavior and cracking susceptibility of the disbonded coating in the X80 steel pipeline by theoretical simulations and experimental measurements

The corrosion behavior and cracking susceptibility of the disbonded coating in the X80 steel pipeline were investigated by different methods. The oxygen content in the trapped solution decreased rapidly with the formation of an airtight disbonded area. The airtight system affected the electrode reaction process, resulting in the inhibition of corrosion in the center of the disbonded area and the more refined surface finish of the sample. The bottom of the disbonded area underwent a relatively intense and accelerated corrosion reaction controlled by the diffusion process. The cracking susceptibility of the X80 steel firstly decreased and then increased in the pointing direction.

Effect of Alternating Stray Current Density on Corrosion Behavior of X80 Steel under Disbonded Coating

In this paper, the effect of alternating stray current (AC) density on the corrosion behavior of X80 steel under disbonded coating was studied by electrochemical methods, wire beam electrode (WBE) technology, and surface observation technology. The results showed that under the interference of different AC densities, the corrosion potential of X80 steel under disbonded coating underwent negative deviation, and the degree of negative deviation increased with the increase of AC density. The corrosion current density of X80 steel under disbonded coating with the action of 0~100 A/m2 AC density had few differences. While the corrosion current density of X80 steel with the action of 200~300 A/m2 AC density increased and the corrosion current density was higher than that under low AC density. The cathode area of the wire beam electrode under disbonded coating is mainly distributed outside and the edge of the gap between disbonded coating and X80 steel, while the anode area is mainly distributed inside the gap.

Microenvironment evolution and SCC behavior of subsea pipeline within disbonded coating crevice in a seawater environment under cathodic protection

Purpose This paper aims to make clear the sensitive zone of subsea pipeline to stress corrosion cracking (SCC) under a disbonded coating. Design/methodology/approach The change of microenvironment under a disbonded coating in artificial seawater was analyzed by using a rectangular crevice cell. The SCC behavior of subsea pipeline was studied by slow strain rate tensile tests. Findings The microenvironment at the crevice bottom exhibits obvious acidification, Cl- aggregation and cathodic protection potential (CP) rise. Accordingly, the susceptibility of X70 steels to SCC is high due to the intensive anodic dissolution effect. At the opening, hydrogen atom can access into the steel and induce hydrogen embrittlement effect on account of the applied over-protected CP potential, resulting in a relatively high susceptibility to SCC. The corrosiveness of the microenvironment at crevice middle, however, is mild with proper CP potential; thus, the susceptibility of X70 steel to SCC here is lower than that obtained at the opening and the crevice bottom. Originality/value A rectangular crevice cell is built to survey the microenvironment evolution under a disbonded coating in situ. The sensitive zone of subsea pipeline to SCC under a disbonded coating is clarified.