The Link Between the Corrosion and calcium carbonate scaling susceptibilities of heat transfer surfaces

The nucleation of CaCO3 scales on copper, graphite, aluminium and mild steel heat transfer surfaces at surface temperatures 54–56°C, from turbulent solutions (Re 22,000) of bulk temperature 30 °C, has been studied using thermal resistance and corrosion potential measurements and scanning electron microscopy. The rate of CaCO3 scale nucleation and growth decreases in the order mild steel > aluminium > copper and graphite. Scale nucleation apparently proceeds from the very outset, throughout an apparent thermal induction period, the end of which appears to be associated with the development of nuclei into aragonite clusters. The differing scaling susceptibilities of the materials are directly related to their corrosion susceptibilities. Studies on aluminium highlight the importance of the nature and integrity of surface oxide films in determining scaling susceptibility. Under the conditions examined, scales consist primarily of aragonite, with small amounts of calcite and vaterite. Mild steel surfaces apparently favour growth of “flower” vaterite.