Formation of calcareous deposits in the tidal zone and its effect on cathodic protection

Abstract

Using the wire beam electrode technique, electrochemical impedance spectroscopy, energy-dispersive X-ray spectroscopy, the formation of calcareous deposits in a tidal zone and its effects on the corrosion and protection of Q235 steel under cathodic protection were studied. Results showed that the production of aragonite CaCO3 crystals significantly reduced from the immersion zone to the high-tide zone, the protective performance of the deposited layer weakened, and the corrosion of the metal intensified. In the immersion zone, the cathodic protection current density decreased, and the potential shifted negatively, indicating that the protection performance of the deposited layer was enhanced and the metal was effectively protected. In the tidal zone, the deposited layer was stratified, and the porosity of the deposited layer increased by dry-wet cycling. During flood tide, the cathodic reaction is accelerated near the waterline, which promotes the corrosion of the metal and the loss of the sacrificial anode under water.