Corrosion monitoring using electrochemical noise and linear polarization resistance in fuel oil combustion gas environment

Abstract

Corrosion monitoring of different steels is carried out online in a combustion rig firing 32 kg/h of fuel oil. Two temperature-controlled probes are designed to allow control of the specimens temperature and the use of electrochemical noise (EN) and linear polarization resistance (LPR) techniques for corrosion monitoring. Two probes are placed where the combustion gas reached a temperature of 850–900°C, and another one at the combustion gas exit where the rig was at 200–240°C. Corrosion rates of an austenitic and a ferritic steel are obtained where the temperature of the combustion gas is 850–900°C, firing fuel oils with different content of Na-V-S. Corrosion monitoring of mild steel is carried out in the test burning a fuel oil with the higher content of Na-V-S by placing a corrosion probe in the low combustion gas temperature zone. The EN results show that this technique is able to assess the corrosion rate in an environment at high temperature where fuel oil ashes deposited and at a temperature high enough where they start to melt and a corrosion process proceeds. Results show that this technique is able to assess the corrosivity of fuel oil ashes originated from fuel oil containing different amounts of sodium, vanadium, and sulfur as corrosion causing impurities. Results of the low-temperature probe show that EN and LPR are able to detect the onset of corrosion on mild steel as a result of sulfuric acid condensation on the probe. However, the corrosion rates are not the same, because localized corrosion is taking place as detected by the EN technique. It is demonstrated that the use of two techniques for corrosion monitoring can give a better understanding of the corrosion process. Electrochemical techniques used to assess the corrosion resistance of alloys at high and low temperatures prove to be a valuable tool for the purposes of materials selection or controlling the main process variables that affect the corrosion resistance of materials in industrial equipment.