Evaluation of 316L Stainless Steel Corrosion Resistance in Solution Simulating the Acid Hydrolysis of Biomass

Abstract

The corrosion resistance of 316L stainless steel in 65 wt % ethanol, 35 wt % water, 1 wt % H 2 SO 4 solution containing different NaCl concentrations and at different temperatures was investigated using open circuit potential measurements, polarization curves, and electrochemical impedance spectroscopy. At 25 C, the minimum NaCl concentration required for occurrence of pitting was 0.58 wt %. In 0.35 wt % NaCl solution, localized corrosion was observed at temperatures higher than 40 C and, depending on the potential, metastable or stable pits were observed. No pits were observed below 40 C in 0.35 wt % NaCl solution. Stainless steels are used as construction materials for key corrosion-resistant equipment in most of the major industries, and especially in chemical, petroleum, processing, and power generation plants. A very thin film, known as the passive film, which is selfhealing in a wide variety of environments, 1-4 provides their corrosion resistance. Due to environmental concerns, there has recently been an increase in the demand for ethanol as a road vehicle fuel. There is therefore, a greater need for studies of the corrosion resistance of materials used in alcohol production plants, and in transportation and storage facilities.Among these stainless steels, the 300 series stands out. The 300 series represents compositional modifications of the classic 18=8 (18% Cr-8% Ni) stainless steel, which has been a popular corrosion-resistant material for some 70 years, to improve pitting, crevice and stress corrosion resistance, high-temperature oxidation resistance and strength, and reduce intergranular corrosion in welded materials. Type 304 is the general-purpose grade, widely used in applications requiring a good combination of corrosion resistance and formability. On the other hand, type 316 contains molybdenum and has greater resistance than type 304 to pitting in marine and chemical industry environments. and pitting corrosion constitutes one of the most important failure mechanisms. Pits cause failure through perforation, and engender stress corrosion cracks.1 Pitting corrosion has been studied for the last few decades and, according to Frankel,6 fundamental studies have focused on characterization of the passive film, the initial stages of passive film breakdown, metastable pitting growth, and the growth of large and stable pits.Solution chloride concentration is a very important parameter influencing pitting formation on stainless steels. Increasing the chloride concentration significantly increases the possibility of pitting. The chloride levels that can be tolerated without the onset of pitting increase with the chromium and molybdenum contents of austenitic and ferritic stainless steels (for example, the minimum chloride ion concentration in 1 mol L À1 H 2 SO 4 for initiation of pitting on pure Fe is 0.3 mmol L À1, while on Fe-18.6Cr-9.9Ni alloy it is 0.1 mol L À1). 1Electrochemical studies of pitting corrosion have found the existence characteristic potentials. Stable pits form at potentials noble to t...

Influence of ethanol, acidity and chloride concentration on the corrosion resistance of AISI 316L stainless steel

“…31 Figures 2a, 2b, and 2c show the SEM micrographs for the polarized steel in the absence and presence of ethanol, respectively. According to X-ray microanalysis previously performed, 14 both images show MnS inclusion dissolution up to the transpassivation region (+1000 mV and +1500 mV vs. Ag/AgCl/KCl sat. ).…”

“…Current density values higher than those obtained in the direct scan (before inverting the scan) indicate that the damaged passive film is not repaired and/or localized corrosion has started, while smaller current values reflect film repair under the same conditions, and therefore the pitting process (stable pit formation) is not initiated. 14 As can be seen in Figure 1, in the reverse scan, the current density decreased exponentially as the potential decreased, indicating that the current density increase in the direct scan was not associated with the localized corrosion, but with transpassivation of the steel.…”

“…The n values are 0.9 and the phase angle values suggest a near-capacitor behavior. 14 Table 4 shows the calculated capacitance and the thickness of the oxide films obtained from the frequency at the maximum imaginary impedance which was estimated from the EEC according to equations 1 and 2. 37…”

“…Our group has started a systematic study on the corrosion resistance of 316L SS in ethanolic solutions. Our lately work 14 reported the evaluation of 316L SS corrosion resistance in a solution that simulates the acid hydrolysis of biomass. In that case, the working solution was composed of 65 wt.% ethanol, 35 wt.% water, 1 wt.% H 2 SO 4 and NaCl contents ranging from 6 × 10 -5 to 0.58 wt.%.…”

Construção de uma célula-autoclave para medidas eletroquímicas a altas temperaturas

“…1,9 As soluções foram preparadas a partir de reagentes com grau analítico e água Milli-Q (18,2 MΩ cm).…”