Influence and Mechanism of SO₄²⁻ Ions on the Pitting Corrosion of Boiler Water-Wall Tubes

This study investigates the influence and mechanism of SO₄²⁻ ions on the pitting corrosion of boiler water-wall tubes. The kinetics of SO₄²⁻ ions on pitting corrosion was assessed by mass gain rate and depth gain. Sample surfaces were examined using transmission reflection metallurgical microscopy, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and x-ray diffraction (XRD). Results indicate that Fe concentration and SO₄²⁻ concentration follow a logarithmic relationship. The adsorption mechanism initiates pitting corrosion, and the local acidification theory of SO₄²⁻ accelerates pitting corrosion. Critical SO₄²⁻ concentrations for the prepas-sivated and un-prepassivated samples are 1 mg L⁻¹ and 0.4 mg L⁻¹, respectively.