Effect of Phosphorus on the Corrosion Behavior of Carbon Steel in Sulfuric Acid

Abstract

This study examined the influence of phosphorus addition on the corrosion resistance of carbon steel for a flue gas desulfurization (FGD) system using electrochemical methods, such as potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in 10 wt% sulfuric acid (H 2 SO 4 ) solution at room temperature. The potentiodynamic measurements indicated that the addition of phosphorus increased the cathodic hydrogen evolution reaction. X-ray photoelectron spectroscopy (XPS) analyses of the corroded surfaces after the immersion testing indicated that the oxidized product of phosphorus-containing steel was composed mainly of iron(II) sulfate (FeSO 4 ), iron(III) sulfate (Fe 2 (SO 4 ) 3 ), and iron(III) phosphate (FePO 4 ). However, these products seem to have no protective property. The experimental results confirmed that phosphorus has a deleterious effect on the corrosion resistance of carbon steels in H 2 SO 4 solution as a result of the higher hydrogen activity.However, in alkali media, it was reported that corrosion resistance of steel is decreased by the presence of phosphorus. 9 This study is part of an ongoing research program to evaluate the corrosion resistance and corrosion mechanism of corrosion-resistant steel for FGD systems. The alloying effect and mechanisms of phosphorus addition on the corrosion properties of carbon steels in H 2 SO 4 were examined through electrochemical tests and surface analyses. EXPERIMENTAL PROCEDURES Materials and Test ConditionCarbon steels in this study were made by hot working. A mixture of the constituent elements was heated to 1,250°C, held for 1 h, subjected to hot rolling to reduce the steel thickness to 0.35 cm, and then annealed at 900°C. For ease of storage and transport, the semifinished steel was coiled at a temperature of 650°C for 1 h, and then cooled in a furnace.Carbon steel plates, 0.35 cm in thickness, were cut into 2.25-cm 2 pieces. Table 1 lists the chemical composition of these steels. Only the phosphorus content differed among the steels. The specimens were cast in a mold using hot acrylic powder, ground with 600-grit silicon carbide (SiC) paper, degreased in an ultrasonic cleaner with ethanol (C 2 H 6 O) for 5 min, cleaned with distilled water, and dried in hot air. All electrochemical measurements were carried out in 1,000 mL of a 10 wt% H 2 SO 4 solution, which is considered to be most representative of the corrosive environment in Korean FGD facilities. The solution was aerated with pure air at a flow rate of 10 cm 3 /min. At least three measurements were run for each specimen to ensure reproducibility.

Microbial communities associated with wet flue gas desulfurization systems

“…The corrosion of steel structures associated with FGD systems is an increasingly prevalent problem (Mansfield and Jeanjaquet, 1987; Hibner and Ross, 1988; Bordziłowski and Darowicki, 1998; Kim et al, 2010). The high solute concentrations and DO of the absorber unit fluids makes them aggressively corrosive solutions, and may give rise to severe pitting corrosion, which has been reported for FGD structures (including systems evaluated in this study) and is often associated with MIC (Franklin et al, 1991; Strehblow, 2007; Moskal, 2011).…”

“…Furthermore, the high TDS of slurry fluids will favor the activities of organisms that are capable of tolerating high osmotic strength fluids. Due to the required oxic conditions, relatively high operating temperatures, high Cl − , and SO 4 2− concentration, and potentially low pH of FGD absorber slurries, they represent an extremely corrosive environment (Mansfield and Jeanjaquet, 1987; Hibner and Ross, 1988; Bordziłowski and Darowicki, 1998; Rajendran et al, 1999; Kim et al, 2010). As such, degradation of the steel walls and other structures is a significant concern for FGD operators.…”

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“…It is of interest to map the distribution of Mn corrosion products and determine the speciation of Mn after corrosion because Mn is present as both MnS inclusions and as alloyed Mn in the steel rebar, [45][46][47] and these different forms of Mn may play a role in the corrosion process.…”

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