Evaluation of water corrosivity using a corrosion rate model for a cooling water system

Abstract

The first part of a corrosion inhibitor model has been developed to be used in a specific Mexican Power Plant. The model takes into account the main operational conditions found in the cooling water such as major corrosive chemical species, a wide pH range, the performance of a commercial corrosion inhibitor (based on tolyltriazol) and the material of the condenser (admiralty). The objective is to replace the old criteria based on Langelier Saturation and Ryznard Stability Index for a better approach that can suggest a variable inhibitor dosage to achieve a desired mpy value in the cooling water system (e. g. 1 mpy). Five pairs of admiralty coupons were sunk in five different beakers containing synthetic cooling water with an increasing concentration factor (I to 5) at fixed pH and temperature. The experiment was repeated at different corrosion inhibitor concentrations, testing three different pH values (6, 7 and 8). Admiralty corrosion rates were obtained (from 0.04 to 2.7 mpy) in the laboratory, in the Presence and absence of a commercial corrosion inhibitor using a jar test and synthetic cooling water The corrosion rates in admiralty were assessed by means of the Linear Polarization Resistance technique. It is demonstrated that, basically admiralty corrosion rate is a function of water chemistry, pH and corrosion inhibitor concentration. Experimental data can be fitted to an empirical equation to predict the performance of a corrosion inhibitor versus inhibitor dosage. The model runs in a personal computer allows the prediction of information related to the treatment cost to achieve a desired mpy value in the cooling water system.