Electrochemistry Study Of Corrosion Resistant Of Carbon Steel Covered By Calcium Carbonate In Geothermal Liquid

There is an abundance of geothermal water resources in china. However, because of the limitation of technology and costs of development of the utilization of this resources is very low especially the high temperature geothermal resources. This paper aims to find characteristics of corrosion behavior of carbon steel under calcium carbonate scale and provide theory instruction for corrosion control. An appropriate testing technique has also been developed.In this paper, the corrosion behavior of Q235 and pipe steel immerged in geothermal water of different temperature(45℃,55℃,65℃,75℃,85℃) was investigated using constant current step technique. The results indicated that both Ecorr and Rp of two materials increase with the immersion time increasing, but the lager fluctuation appeared in the later time, it illustrate that water scale and corrosion product inhibit the process of corrosion, but with the water scale and corrosion product scale off from the surface in the later time, corrosion was accelerated and local corrosion was induced. Combined with SEM and XPS analysis we found that the performance of water scale formed in 65℃was best. With the increase of water temperature, iron oxide would form between the water scale and substrate, and finally resulted in calcium carbonate layer off.In this paper, a complete water scale was formed on steel surface by means of cathodic protection. Samples were immerged in geothermal water for a week under temperature of 45℃,55℃,65℃,75℃,85℃. Ecorr and Rp was used to investigate corrosion behavior. As indicated in the results, At 45℃and 55℃, the water scale with Al-Zn-In alloy protection was dense, thick, its protective effect was better than with zinc protection. When the temperature above 65℃, alumina membranes appeared on the surface of Al-Zn-In sample with pitting, and corrosion was accelerated. Corrosion resistance of Q235 with coating calcium carbonate layer was decreased, because the growth rate of the calcium carbonate layer with a loose structure was high. The calcium carbonate layer with zinc protection was dense. Grain of zinc carbonate and zinc oxide was large and layer had a loose structure. With the temperature increasing, the growth rate of the calcium carbonate layer was high and grain was acicular, Corrosion resistance of Q235 sample under the calcium carbonate loose layer was decreased. Corrosion resistance of Q235 sample with Al-Zn-In alloy protection was best at 55℃. When the temperature above 65℃sacrificial anodes using zinc was better than using Al-Zn-In alloy.