Local environment under simulated disbonded coating on steel pipelines in soil solution |
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Authors: | Maocheng Yan Jianqiu Wang Enhou Han Wei Ke |
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Affiliation: | aEnvironmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China |
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Abstract: | Taking advantage of microelectrode technique, the local potential and pH in a crevice simulating disbonded coating on X70 pipeline steel were investigated as a function of cathodic protection (CP) in a near neutral pH soil bulk solution bubbled with 5% CO2/N2 gas. The experimental potential–pH (E–pH) diagrams were established for the steel in the crevice. Stress corrosion cracking (SCC) susceptibility of the steel in the local environment in the crevice was analyzed based on the experimental E–pH diagrams. The results showed that the local steel potential in the deep of the crevice was independent on CP potential applied at the opening. Due to the effect of the atmospheric CO2, a near-neutral pH local environment promoting near-neutral pH SCC (also known as transgranular SCC, TGSCC) might be harbored in the crevice even with normal CP at the opening. During CP interruption, the steel potential decay and CO2 absorption (pH decrease) might shift E–pH points into a susceptibility region of near-neutral pH SCC. |
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Keywords: | B Microelectrode technique C Cathodic protection C Disbonded coatings C Stress corrosion C Crevice corrosion |
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