Mitigation of Fireside Corrosion of Stainless Steel in Power Plants: A Laboratory Study of the Influences of SO₂ and KCl on Initial Stages of Corrosion

Abstract

The effect of SO2(g) on the initial oxidation of the stainless-steel 304L, sprayed with 0.1 mg/cm2 KCl and exposed in 5% O2 and 40% H2O at 600 °C, was investigated. In the absence of SO2(g), KCl accelerates the corrosion attack by the formation of K2CrO4. The reaction with KCl depletes the oxide in chromium and converts it into an iron-rich, poorly protective oxide. When SO2(g) was introduced to the gas flow, KCl rapidly transformed into K2SO4. In contrast to KCl, K2SO4 does not form K2CrO4. Hence, it does not accelerate the corrosion rate. Although the conversion of KCl to K2SO4 is fast, the corrosion rate of KCl samples exposed in the presence of SO2(g) is higher than samples exposed in the presence of K2SO4. It is therefore suggested that small amounts of unreacted KCl react initially with the protective oxide, forming K2CrO4, which depletes the oxide in chromium. However, because of the presence of SO2(g), K2CrO4 immediately reacts with SO2(g) to form K2SO4. This study shows that the initial stages of the corrosion attack are of great importance. The initial complex interactions between the flue gas, deposit, and oxide scale affect the future corrosion resistance of the steel.

Deposit Shedding in Biomass-Fired Boilers: Shear Adhesion Strength Measurements

“…Several corrosion studies in literature indicate that the rate of corrosion decreases considerably over time [2,5,12]. The change in melt fraction brought about by increasing corrosion is probably not significant enough to observe reliable changes in adhesion strength.…”

Oxidation After Breakdown of the Chromium-Rich Scale on Stainless Steels at High Temperature: Internal Oxidation

“…In an analogous manner, the breakdown of the initial protective oxide in the presence of alkali [8] was explained by the formation of alkali chromate in a reaction with the protective scale. Addition of small amounts of sulfur dioxide has been shown to prolong the incubation time for breakaway oxidation in the presence of KCl and to slow down scale growth after breakaway [20]. [16,[21][22][23].…”

“…5a, 6a; Table 2). This implies that SO 2 not only delays the breakdown of the protective scale by converting the corrosive KCl to non-reactive K 2 SO 4 , it also slows down the growth of the iron-rich scale after breakaway [20].…”

“…Thus, the breakdown of the initial protective oxide in the presence of water vapor/alkali was explained by the formation of chromium(VI) oxide hydroxide/alkali chromate in a reaction with the protective scale temperatures [4,8,18,19]. Addition of small amounts of sulfur dioxide has been shown to prolong the incubation time for breakaway oxidation in the presence of KCl and to slow down scale growth after breakaway [20]. At low oxygen activities, evaporation of chromium (VI) oxide hydroxide is negligible and the accelerated oxidation of stainless steels in H 2 ?…”

Effect of Water Vapor on High-Temperature Corrosion under Conditions Mimicking Biomass Firing

“…Other studies [11,[22][23][24][25][26][27] suggest that SO2 in the flue gas can affect the corrosion process in a couple of ways:…”