Study of the formation of calcareous deposits on cathodically protected steel in Baltic sea water

The purpose of this paper is to investigate whether the sedimentation of calcareous deposits occurs on cathodically protected steel in Baltic sea water.

Steel electrodes were cathodically polarized in natural Baltic sea water at potential +0.150 V vs Zn electrode in potentiostatic mode. During exposure chronoamperometric measurements were carried out. After the exposure, the electrode's surface was examined by scanning atomic force microscope (AFM) and by scanning electron microscope (SEM). Deposit composition was examined by energy‐dispersive X‐ray spectroscopy (EDX). Comparative investigation was carried out in 1 percent NaCl solution (comparable to the salinity of Baltic sea water).

During cathodic polarization in Baltic sea water, non‐conducting calcareous deposits developed on steel surface. These deposits significantly lowered the cathodic current demand. Morphology and EDX spectroscopy of the deposit indicated that it was built mainly of aragonite (polymorph of CaCO3). No non‐conducting deposits on cathodically protected steel electrodes developed in 1 percent NaCl solution.

Composition of Baltic sea water favours the formation of calcareous deposits on cathodically protected steel. Sedimentation is a beneficial and desired phenomenon from the point of view of cathodic protection system of maritime construction as it facilitates polarization. Evolution of calcareous deposits should be taken into account as one of the environmental factors when designing a cathodic protection system.