CATHODIC POLARIZATION AGAINST CREVICE CORROSION OF X70 PIPELINE STEEL IN SIMULATED SOLUTION OF KU'ERLE SOIL IN XINJIANG
SONG Yiquan; DU Cuiwei;ZHANG Xin; LI Xiaogang
Cite this article:
SONG Yiquan; DU Cuiwei; ZHANG Xin; LI Xiaogang. CATHODIC POLARIZATION AGAINST CREVICE CORROSION OF X70 PIPELINE STEEL IN SIMULATED SOLUTION OF KU'ERLE SOIL IN XINJIANG. Acta Metall Sin, 2006, 42(3): 305-310 .
Abstract A wedge-shaped crevice cell used to model previously disbonded coating holiday of X70 pipeline steel under impressed current cathodic protection in simulated solution of desert soil of Ku’erle in Xinjiang. Distributions of polarization potentials and current along long direction of the wedge-shaped crevice were measured in different time intervals at different opening control potentials (-850mV, -1000mV and -1150mV vs CSE) and at different crevice opening thickness (0.15mm, 0.30mm and 0.45mm). The influences of applied control potentials and crevice thickness on polarization potentials, polarization current and pH value in crevice were investigated deeply. It was showed that gradients of polarization potential and current in crevice gradually decreased with times, due to the depletion of dissolved oxygen. It was found again that, a negative shift of opening control potentials, and increase of crevice opening thickness resulted in the decrease of polarization potentials, and the increase of polarization current in crevice. On the other hand, the pH value in crevice gradually increased also with more negative opening control potential, and with increase of the opening thickness. At the same control potential, the pH value from crevice opening to bottom increased first, then stabilized at a definite value. Moreover, more negative shift of the control potentials and bigger crevice opening thickness can make the stable pH value increase, but the increasing rate gradually decreased.
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