Abstract
In this article, wire beam electrode (WBE) was used to evaluate the corrosion behavior of ND steel in environmental acid atmosphere with different partial pressure of CO2. Meanwhile, corrosion products and surface morphology analysis also used to support this research. The results showed that the corrosion behavior began from the edge of droplet in dew point corrosion, and gradually spread to the center of it. The spread speed would be increasing with CO2 partial pressure enhance, which was 24h in 5% CO2 and 4h in 50% CO2. Corrosion current density in the edge of droplet can form the “cathode-anode-cathode ring” structure and disappears gradually as the corrosion time was going. Corrosion morphology observation results showed three ring shapes region and different elemental composition of different corrosion products, which is correspondence with the “cathode-anode We-cathode ring” structure measured in WBE experiments. The results showed that the reaction gradually transferred to the uniform corrosion on electrode surface when the dew point corrosion reaction reaching the late stage. It comes from the dissolution, diffusion and reaction of gaseous corrosion medium of CO2 and O2.
Highlights
Dew point corrosion (DPC) is the most important type of high temperature equipment corrosion (Dan et al, 2011; Wang et al, 2013)
As for DPC, the corrosion media is different to the common thin electrolyte film, the acid atmosphere such as SO2, SO3, CO2 and HCl are became the corrosion media instead O2 to attack the base metal (Shu et l., 1999; Huijbregts and Leferink, 2004)
All surface of wire beam electrode (WBE) cell was covered by distilled water droplets, and the abscissa and ordinate coordinates represent different electrode positions
Summary
Dew point corrosion (DPC) is the most important type of high temperature equipment corrosion (Dan et al, 2011; Wang et al, 2013). Some researchers’ consideration that DPC is a kind of special corrosion in thin electrolyte film, and the corrosion rate was due to the rate of corrosion media mass-transfer process. As for DPC, the corrosion media is different to the common thin electrolyte film, the acid atmosphere such as SO2, SO3, CO2 and HCl are became the corrosion media instead O2 to attack the base metal (Shu et l., 1999; Huijbregts and Leferink, 2004). The chemical compositions of this steel are kept according to the requirements of the standards, and it used to make the electrodes and observation samples
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