EROSION-CORROSION BEHAVIOR OF STEELS IN A PARTICULATE-CONTAINING PULPING LIQUOR ENVIRONMENT AT ELEVATED TEMPERATURE

摘要

Erosion-corrosion, is a major problem in pulp/paper mill equipment. Erosion-corrosion in steels under caustic conditions is a challenging subject due to the particulate fluid with organics and non-Newtonian behavior. Fluid properties, liquor composition and process parameters affect corrosion rates in this regime. Studies have suggested that the flow may interfere with passive film formation in caustic conditions and significantly increase the corrosion rate. In order to better understand the mechanism of this corrosion process, electrochemical tests were performed on UNS G10180, UNS S31603 and UNS S32205, used in the construction of pulp/paper machinery components exposed to caustic environments. Rotating cylinder electrode (RCE) tests with linear polarization resistance (LPR) method were used to get instantaneous corrosion in a simulated white liquor (WL) solution with hard particles simulating conditions for the digesters or evaporators. Repassivation behavior of alloys under flow conditions was studied by using scratch tests. The results showed that G10180 was resilient at room temperature but corroded actively at elevated temperature, while S31603 showed sensitivity to flow especially at elevated temperature. S32205 provided good performance in the tested temperatures and environments without significant flow effects. Finally, a practical, qualitative measurement of "potential shift" after a scratch was introduced.