Electrochemical corrosion monitoring has been used to evaluate fireside corrosion of coal fired boilers materials under low NOX operations. The reducing environments which are prevalent under these firing conditions can lead to the deposition/formation of non-protective iron sulfide films on the boiler tubes, resulting in excessive corrosion attack. In order to mitigate the boiler tube corrosion problems, it is common practice to weld overlay the boiler tubes with alloy C276. Corrosion of typical boiler tube material and C276 has been monitored electrochemically using a combination of Linear Polarisation Resistance (LPR), Harmonic Distortion Analysis (HDA), Electrochemical Current Noise (ECN), and Solution Resistance (Rs) measurements. The electrochemical corrosion monitoring instrumentation used in this work has been designed to operate under extreme conditions, with embedded algorithms to minimise the effects of electrical interference and provide simplified data analysis. Corrosion measurements for the field trials were updated at five minute intervals to provide a continuous record of the changes in corrosion behaviour. Electrochemical probes, using a two electrode configuration, have been designed specifically for this application where access is restricted. The probes are designed to be inserted into the webbing between the boiler tubes, where they will experience similar temperatures and heat flux as the boiler tubes. Results of both laboratory tests, and field trials in an operating boiler are presented.
Keywords: fireside corrosion, Hastelloy, low NOX, corrosion monitoring, Linear Polarisation Resistance, Harmonic Distortion Analysis, Electrochemical Noise