Effect of Pseudomonas aeruginosa Marine Biofilm on Microbial Corrosion of 2707 Super Duplex Stainless Steel

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Microbial corrosion (MIC) is a major problem in many industries because it can lead to huge economic losses. Super duplex stainless steel 2707 (2707 HDSS) is used in marine environments due to its excellent chemical resistance. However, its resistance to MIC has not been experimentally demonstrated. This study examined the behavior of MIC 2707 HDSS caused by the marine aerobic bacterium Pseudomonas aeruginosa. Electrochemical analysis showed that in the presence of the Pseudomonas aeruginosa biofilm in the 2216E medium, the corrosion potential changed positively, and the corrosion current density increased. The results of X-ray photoelectron spectroscopy (XPS) analysis showed a decrease in the Cr content on the sample surface under the biofilm. Analysis of the pit images showed that Pseudomonas aeruginosa biofilms produced a maximum pit depth of 0.69 µm after 14 days of culture. Although this is small, it suggests that 2707 HDSS are not completely immune to the effects of P. aeruginosa biofilms on MIC.
Duplex stainless steel (DSS) is widely used in various industries due to the perfect combination of excellent mechanical properties and corrosion resistance1,2. However, localized pitting may still occur, which may affect the integrity of this steel 3, 4 . DSS is not protected against microbial corrosion (MIC)5,6. Although the application range of DSS is very wide, there are still environments where the corrosion resistance of DSS is not sufficient for long term use. This means that more expensive materials with higher corrosion resistance are required. Jeon et al.7 found that even super duplex stainless steel (SDSS) has some limitations in terms of corrosion resistance. Therefore, there is a need for super duplex stainless steels (HDSS) with higher corrosion resistance in certain applications. This led to the development of highly alloyed HDSS.
The corrosion resistance of DSS is determined by the ratio of α-phase to γ-phase and areas depleted in Cr, Mo and W adjacent to the secondary phases8,9,10. HDSS contains a high content of Cr, Mo and N11, which gives it excellent corrosion resistance and a high value (45-50) equivalent pitting resistance value (PREN), which is defined by wt.% Cr + 3.3 (wt.% Mo + 0, 5 wt % W) + 16 wt %. N12. Its excellent corrosion resistance depends on a balanced composition containing approximately 50% ferritic (α) and 50% austenitic (γ) phases. HDSS has improved mechanical properties and higher chlorine resistance compared to conventional DSS13. Characteristics of chemical corrosion. Improved corrosion resistance extends the use of HDSS in more aggressive chloride environments such as marine environments.
MIC is a significant problem in many industries, including oil and gas and water supply14. MIC accounts for 20% of all corrosion damage15. MIC is a bioelectrochemical corrosion that can be observed in many environments16. The formation of biofilms on metal surfaces changes the electrochemical conditions and thus influences the corrosion process. It is generally accepted that MIC corrosion is caused by biofilms14. Electrogenic microorganisms eat away metals in order to obtain energy for survival17. Recent MIC studies have shown that EET (extracellular electron transfer) is the limiting factor for MIC induced by electrogenic microorganisms. Zhang et al.18 demonstrated that electron mediators accelerate electron transfer between Desulfovibrio vulgaris sessile cells and 304 stainless steel, resulting in more severe MIC attack. Anning et al. 19 and Wenzlaff et al. 20 have shown that biofilms of corrosive sulfate-reducing bacteria (SRBs) can absorb electrons directly from metal substrates, resulting in severe pitting.
DSS is known to be susceptible to MIC in media containing SRBs, iron-reducing bacteria (IRBs), etc. 21 . These bacteria cause localized pitting on the surface of the DSS under the biofilm22,23. Unlike DSS, little is known about the MIC HDSS24.
Pseudomonas aeruginosa is a Gram-negative, motile, rod-shaped bacterium that is widely distributed in nature25. Pseudomonas aeruginosa is also the main microbiota responsible for the MIC of steel in the marine environment26. Pseudomonas species are directly involved in corrosion processes and are recognized as the first colonizers during biofilm formation27. Mahat et al. 28 and Yuan et al. 29 demonstrated that Pseudomonas aeruginosa tends to increase the corrosion rate of mild steel and alloys in aquatic environments.
The main goal of this work is to study the MIC properties of 2707 HDSS caused by the marine aerobic bacterium Pseudomonas aeruginosa using electrochemical methods, surface analysis methods and corrosion product analysis. Electrochemical studies including open circuit potential (OCP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and dynamic potential polarization were performed to study the behavior of the MIC 2707 HDSS. Energy dispersive spectroscopy (EDS) analysis is performed to detect chemical elements on corroded surfaces. In addition, the stability of oxide film passivation under the influence of a marine environment containing Pseudomonas aeruginosa was determined by X-ray photoelectron spectroscopy (XPS). The depth of the pits was measured under a confocal laser scanning microscope (CLSM).
Table 1 shows the chemical composition of 2707 HDSS. Table 2 shows that 2707 HDSS has excellent mechanical properties with a yield strength of 650 MPa. On fig. 1 shows the optical microstructure of solution heat treated 2707 HDSS. Elongated bands of austenitic and ferritic phases without secondary phases can be seen in a microstructure containing approximately 50% austenitic and 50% ferritic phases.
On fig. 2a shows the open circuit potential (Eocp) versus exposure time for 2707 HDSS in 2216E abiotic medium and Pseudomonas aeruginosa broth for 14 days at 37°C. It was found that the most pronounced changes in Eocp occurred during the first 24 hours. Eocp values ​​in both cases peaked at about -145 mV (versus SCE) at about 16 hours and then dropped sharply to -477 mV (versus SCE) and -236 mV (versus SCE) for non-biological samples and P for relative SCE) patina leaves, respectively. After 24 hours, the Eocp value of Pseudomonas aeruginosa 2707 HDSS remained relatively stable at -228 mV (compared to SCE), while the corresponding value for the non-biological sample was approximately -442 mV (compared to SCE). Eocp in the presence of Pseudomonas aeruginosa was quite low.
Electrochemical testing of 2707 HDSS samples in abiotic media and Pseudomonas aeruginosa broth at 37°C:
(a) Change in Eocp with exposure time, (b) polarization curve at day 14, (c) change in Rp with exposure time, (d) change in corr with exposure time.
Table 3 shows the electrochemical corrosion parameters of 2707 HDSS samples exposed to abiotic and P. aeruginosa inoculated media over a period of 14 days. Tangential extrapolation of the anodic and cathodic curves to the intersection point allowed the determination of corrosion current density (icorr), corrosion potential (Ecorr) and Tafel slope (βα and βc) according to standard methods30,31.
As shown in Figure 2b, the upward shift of the P. aeruginosa curve resulted in an increase in Ecorr compared to the abiotic curve. The icorr value of the sample containing Pseudomonas aeruginosa, proportional to the corrosion rate, increased to 0.328 µA cm-2, which is four times greater than that of the non-biological sample (0.087 µA cm-2).
LPR is a classic electrochemical method for non-destructive express analysis of corrosion. It has also been used to study MIC32. On fig. 2c shows the change in the polarization resistance (Rp) depending on the exposure time. A higher Rp value means less corrosion. Within the first 24 hours, Rp 2707 HDSS peaked at 1955 kΩ cm2 for non-biological specimens and 1429 kΩ cm2 for Pseudomonas aeruginosa specimens. Figure 2c also shows that the Rp value decreased rapidly after one day and then remained relatively unchanged over the next 13 days. The Rp value for the Pseudomonas aeruginosa test specimen is about 40 kΩ cm2, which is much lower than the 450 kΩ cm2 value for the non-biological test specimen.
The value of icorr is proportional to the uniform corrosion rate. Its value can be calculated from the following Stern-Giri equation:
According to Zoe et al. 33 the Tafel slope B was taken as a typical value of 26 mV/dec in this work. On fig. 2d shows that the icorr of the 2707 abiotic strain remained relatively stable, while the icorr of the Pseudomonas aeruginosa band fluctuated strongly with a large jump after the first 24 hours. The icorr value of the Pseudomonas aeruginosa test sample was an order of magnitude higher than that of the non-biological control. This trend is consistent with the results of polarization resistance.
EIS is another non-destructive method used to characterize electrochemical reactions at a corrosion interface34. Impedance spectra and capacitance calculations of strips exposed to abiotic media and solutions of Pseudomonas aeruginosa, Rb is the resistance of the passive/biofilm formed on the surface of the strip, Rct is the charge transfer resistance, Cdl is the electrical double layer. ) and QCPE constant phase element (CPE) parameters. These parameters were further analyzed by comparing the data with an equivalent electrical circuit (EEC) model.
On fig. 3 shows typical Nyquist plots (a and b) and Bode plots (a’ and b’) of 2707 HDSS samples in abiotic media and Pseudomonas aeruginosa broth at various incubation times. In the presence of Pseudomonas aeruginosa, the diameter of the Nyquist loop decreases. The Bode plot (Fig. 3b’) shows the increase in total impedance. Information about the relaxation time constant can be obtained from phase maxima. On fig. 4 shows the physical structures and the corresponding EEC based on a single-layer (a) and two-layer (b). CPE is introduced into the EEC model. Its admittance and impedance are expressed as follows:
Two physical models and corresponding equivalent circuits for fitting the 2707 HDSS coupon impedance spectrum:
Where Y0 is the magnitude of the CPE, j is the imaginary number or (−1)1/2, ω is the angular frequency, and n is the CPE power factor less than one35. The charge transfer resistance inversion (ie 1/Rct) corresponds to the corrosion rate. A lower Rct value means a higher corrosion rate27. After 14 days of incubation, the Rct of the test sample of Pseudomonas aeruginosa reached 32 kΩ cm2, which is much less than the 489 kΩ cm2 of the non-biological test sample (Table 4).
CLSM images and SEM images in fig. 5 clearly show that the biofilm coverage on the surface of HDSS sample 2707 was very dense after 7 days. However, after 14 days the biofilm coating became sparse and some dead cells appeared. Table 5 shows the biofilm thickness of 2707 HDSS samples after 7 and 14 days of exposure to Pseudomonas aeruginosa. The maximum biofilm thickness changed from 23.4 µm after 7 days to 18.9 µm after 14 days. The average biofilm thickness also confirmed this trend. It decreased from 22.2 ± 0.7 μm after 7 days to 17.8 ± 1.0 μm after 14 days.
(a) 3-D CLSM image at 7 days, (b) 3-D CLSM image at 14 days, (c) SEM image at 7 days, and (d) SEM image at 14 days.
EMF revealed chemical elements in biofilm and corrosion products on samples exposed to Pseudomonas aeruginosa for 14 days. On fig. Figure 6 shows that the content of C, N, O, P in the biofilm and corrosion products is much higher than in pure metal, since these elements are associated with the biofilm and its metabolites. Microorganisms require only trace amounts of Cr and Fe. The high content of Cr and Fe in the biofilm and corrosion products on the surface of the sample indicate the loss of elements in the metal matrix as a result of corrosion.
After 14 days, pits with and without P. aeruginosa were observed in medium 2216E. Before incubation, the surface of the samples was smooth and without defects (Fig. 7a). After incubation and removal of biofilm and corrosion products, the deepest pits on the surface of the sample were examined using CLSM, as shown in Fig. 7b and c. No obvious pitting was found on the surface of the non-biological control (maximum pit depth 0.02 µm). The maximum pit depth caused by Pseudomonas aeruginosa was 0.52 µm after 7 days and 0.69 µm after 14 days, based on the average maximum pit depth from 3 samples (10 maximum pit depths were selected for each sample) and reached 0. 42 ± 0.12 µm. and 0.52 ± 0.15 µm, respectively (Table 5). These dimple depth values ​​are small but important.
(a) before exposure; (b) 14 days in an abiotic environment; (c) 14 days in P. aeruginosa broth.
On fig. Table 8 shows the XPS spectra of various sample surfaces, and the chemistry analyzed for each surface is summarized in Table 6. In Table 6, the atomic percentages of Fe and Cr were much lower in the presence of P. aeruginosa (samples A and B) than in the non-biological control strips. (samples C and D). For a sample of Pseudomonas aeruginosa, the Cr 2p core level spectral curve was fitted to four peak components with binding energies (BE) of 574.4, 576.6, 578.3 and 586.8 eV, which were assigned to Cr, Cr2O3, CrO3 and Cr(OH)3, respectively (Fig. 9a and b). For nonbiological samples, the spectra of the core level Cr 2p in Figs. 9c and d contain the two main peaks of Cr (BE 573.80 eV) and Cr2O3 (BE 575.90 eV), respectively. The most striking difference between the abiotic coupon and the P. aeruginosa coupon was the presence of Cr6+ and a relatively high fraction of Cr(OH)3 (BE 586.8 eV) under the biofilm.
Broad surface XPS spectra of 2707 HDSS samples in two media for 7 and 14 days, respectively.
(a) 7 day P. aeruginosa exposure, (b) 14 day P. aeruginosa exposure, (c) 7 day abiotic exposure, (d) 14 day abiotic exposure.
HDSS exhibits a high level of corrosion resistance in most environments. Kim et al.2 reported that HDSS UNS S32707 was identified as a highly doped DSS with PREN greater than 45. The PREN value of HDSS sample 2707 in this work was 49. This is due to the high Cr content and high levels of Mo and Ni, which are useful in acidic environments and environments with a high content of chlorides. In addition, the well-balanced composition and defect-free microstructure provide structural stability and corrosion resistance. Despite excellent chemical resistance, the experimental data in this work show that 2707 HDSS is not completely immune to Pseudomonas aeruginosa biofilm MICs.
Electrochemical results showed that the corrosion rate of 2707 HDSS in Pseudomonas aeruginosa broth increased significantly after 14 days compared to the non-biological environment. In Figure 2a, a decrease in Eocp was observed both in the abiotic medium and in P. aeruginosa broth during the first 24 hours. After that, the biofilm finishes covering the surface of the sample and Eocp becomes relatively stable. However, the biotic Eocp level was much higher than the abiotic Eocp level. There are reasons to believe that this difference is associated with the formation of P. aeruginosa biofilms. On fig. 2g, the icorr value of 2707 HDSS reached 0.627 µA cm-2 in the presence of Pseudomonas aeruginosa, which is an order of magnitude higher than that of the non-biological control (0.063 µA cm-2), which is consistent with the Rct value measured by EIS. During the first few days, the impedance values ​​in the P. aeruginosa broth increased due to the attachment of P. aeruginosa cells and biofilm formation. However, the impedance decreases when the biofilm completely covers the sample surface. The protective layer is attacked primarily due to the formation of biofilm and biofilm metabolites. Therefore, corrosion resistance decreases over time, and deposits of Pseudomonas aeruginosa cause localized corrosion. The trends in abiotic environments are different. The corrosion resistance of the non-biological control was much higher than the corresponding value of the samples exposed to Pseudomonas aeruginosa broth. In addition, for abiotic samples, the Rct 2707 HDSS value reached 489 kΩ cm2 on day 14, which is 15 times higher than in the presence of Pseudomonas aeruginosa (32 kΩ cm2). Thus, 2707 HDSS has excellent corrosion resistance in a sterile environment, but is not protected from MIC attack by Pseudomonas aeruginosa biofilm.
These results can also be observed from the polarization curves in Figs. 2b. Anodic branching is associated with Pseudomonas aeruginosa biofilm formation and metal oxidation reactions. At the same time, the cathodic reaction is the reduction of oxygen. The presence of P. aeruginosa significantly increased the corrosion current density, which was about an order of magnitude higher than in the abiotic control. This indicated that the Pseudomonas aeruginosa biofilm enhanced the localized corrosion of 2707 HDSS. Yuan et al.29 found that the corrosion current density of a 70/30 Cu-Ni alloy was increased by Pseudomonas aeruginosa biofilm. This may be due to the biocatalysis of oxygen reduction by Pseudomonas aeruginosa biofilm. This observation may also explain the MIC 2707 HDSS in this work. Aerobic biofilms can also reduce the oxygen content underneath them. Thus, the refusal to repassivate the metal surface with oxygen may be a factor contributing to MIC in this work.
Dickinson et al. 38 suggested that the rate of chemical and electrochemical reactions directly depends on the metabolic activity of bacteria attached to the sample surface and on the nature of the corrosion products. As shown in Figure 5 and Table 5, the number of cells and biofilm thickness decreased after 14 days. This can reasonably be explained by the fact that after 14 days most of the anchored cells on the 2707 HDSS surface died due to nutrient depletion in the 2216E medium or release of toxic metal ions from the 2707 HDSS matrix. This is a limitation of batch experiments.
In this work, a Pseudomonas aeruginosa biofilm promoted local depletion of Cr and Fe under the biofilm on the surface of 2707 HDSS (Fig. 6). In Table 6, Fe and Cr decreased in sample D compared to sample C, indicating that Fe and Cr dissolution caused by the P. aeruginosa biofilm was maintained after the first 7 days. The 2216E environment is used to simulate the marine environment. It contains 17700 ppm Cl-, which is comparable to its content in natural sea water. The presence of 17700 ppm Cl- was the main reason for the decrease in Cr in 7-day and 14-day non-biological samples analyzed by XPS. Compared to the test sample of Pseudomonas aeruginosa, the dissolution of Cr in the abiotic test sample is much less due to the strong resistance of 2707 HDSS to chlorine in the abiotic environment. On fig. 9 shows the presence of Cr6+ in the passivating film. This may be related to the removal of Cr from steel surfaces by P. aeruginosa biofilms, as suggested by Chen and Clayton39.
Due to bacterial growth, the pH values ​​of the medium before and after incubation were 7.4 and 8.2, respectively. Thus, corrosion of organic acids is unlikely to contribute to this work under P. aeruginosa biofilms due to the relatively high pH in the bulk medium. The pH of the non-biological control medium did not change significantly (from initial 7.4 to final 7.5) during the 14 day test period. The increase in pH in the inoculum medium after incubation was associated with the metabolic activity of Pseudomonas aeruginosa, and the same effect on pH was found in the absence of the test strip.
As shown in fig. 7, the maximum pit depth caused by the Pseudomonas aeruginosa biofilm was 0.69 µm, which is significantly greater than in the abiotic medium (0.02 µm). This agrees with the above electrochemical data. Under the same conditions, the pit depth of 0.69 µm is more than ten times smaller than the 9.5 µm value specified for 2205 DSS40. These data show that 2707 HDSS exhibits better resistance to MICs than 2205 DSS. This is not surprising since 2707 HDSS has a higher Cr level, which allows longer passivation, makes Pseudomonas aeruginosa more difficult to depassivate, and starts the process without harmful secondary precipitation Pitting41.
In conclusion, MIC pitting was found on 2707 HDSS surfaces in Pseudomonas aeruginosa broth, while pitting was negligible in abiotic media. This work shows that 2707 HDSS has better resistance to MIC than 2205 DSS, but it is not completely immune to MIC due to Pseudomonas aeruginosa biofilm. These results assist in the selection of suitable stainless steels and life expectancy for the marine environment.
The 2707 HDSS samples were provided by the School of Metallurgy, Northeastern University (NEU), Shenyang, China. The elemental composition of 2707 HDSS is shown in Table 1, which was analyzed by the Materials Analysis and Testing Department of Northeastern University. All samples were treated for solid solution at 1180°C for 1 hour. Prior to corrosion testing, 2707 HDSS coin steel with an exposed surface area of ​​1 cm2 was polished to 2000 grit with silicon carbide sandpaper and then further polished with a 0.05 µm Al2O3 powder slurry. The sides and bottom are protected with inert paint. After drying, the samples were washed with sterile deionized water and sterilized with 75% (v/v) ethanol for 0.5 h. They were then air-dried under ultraviolet (UV) light for 0.5 h before use.
Marine strain Pseudomonas aeruginosa MCCC 1A00099 was purchased from Xiamen Marine Culture Collection (MCCC), China. Marine 2216E liquid medium (Qingdao Hope Biotechnology Co., Ltd., Qingdao, China) was used to culture Pseudomonas aeruginosa in 250 ml flasks and 500 ml electrochemical glass cells under aerobic conditions at 37°C. Medium contains (g/l): 19.45 NaCl, 5.98 MgCl2, 3.24 Na2SO4, 1.8 CaCl2, 0.55 KCl, 0.16 Na2CO3, 0.08 KBr, 0.034 SrCl2, 0.08 SrBr2 , 0.022 H3BO3, 0.004 NaSiO3, 0.008, 0.008 Na4F0H20PO. 1.0 yeast extract and 0.1 iron citrate. Autoclave at 121 °C for 20 min prior to inoculation. Sessile and planktonic cells were counted under a light microscope using a hemocytometer at 400x magnification. The initial concentration of planktonic P. aeruginosa cells immediately after inoculation was approximately 106 cells/mL.
Electrochemical tests were carried out in a classic three-electrode glass cell with a medium volume of 500 ml. A platinum sheet and a saturated calomel electrode (SCE) were connected to the reactor through a Luggin capillary filled with a salt bridge and served as counter and reference electrodes, respectively. To create the working electrode, rubber-coated copper wire was attached to each sample and coated with epoxy, leaving about 1 cm2 of surface area on one side for the working electrode. During electrochemical measurements, the samples were placed in the 2216E medium and kept at a constant incubation temperature (37°C) in a water bath. OCP, LPR, EIS and potential dynamic polarization data were measured using an Autolab potentiostat (Reference 600TM, Gamry Instruments, Inc., USA). LPR tests were recorded at a scan rate of 0.125 mV s-1 in the -5 and 5 mV range and Eocp with a sampling rate of 1 Hz. EIS was performed at steady state Eocp using an applied voltage of 5 mV with a sinusoid over a frequency range of 0.01 to 10,000 Hz. Before the potential sweep, the electrodes were in open circuit mode until a stable free corrosion potential of 42 was reached. With. Each test was repeated three times with and without Pseudomonas aeruginosa.
Samples for metallographic analysis were mechanically polished with 2000 grit wet SiC paper and then polished with a 0.05 µm Al2O3 powder slurry for optical observation. Metallographic analysis was performed using an optical microscope. The sample was etched with 10 wt% potassium hydroxide solution43.
After incubation, wash 3 times with phosphate buffered saline (PBS) (pH 7.4 ± 0.2) and then fix with 2.5% (v/v) glutaraldehyde for 10 hours to fix the biofilm. Subsequent dehydration with ethanol in a stepped series (50%, 60%, 70%, 80%, 90%, 95% and 100% by volume) before air drying. Finally, a gold film was sputtered onto the surface of the sample to provide conductivity for SEM44 observation. The SEM images are focused on the location with the most established P. aeruginosa cells on the surface of each sample. EMF analysis was carried out to detect chemical elements. To measure the depth of the pit, a Zeiss confocal laser scanning microscope (CLSM) (LSM 710, Zeiss, Germany) was used. To observe corrosion pits under the biofilm, the test sample was first cleaned according to the Chinese National Standard (CNS) GB/T4334.4-2000 to remove corrosion products and biofilm from the surface of the test sample.
X-ray photoelectron spectroscopy (XPS, ESCALAB250 Surface Analysis System, Thermo VG, USA) analysis using a monochromatic X-ray source (Al Kα line with an energy of 1500 eV and a power of 150 W) in a wide range of binding energies 0 below the standard conditions of –1350 eV. Record high resolution spectra using 50 eV pass energy and 0.2 eV step size.
Remove the incubated sample and gently wash it with PBS (pH 7.4 ± 0.2) for 15 s45. To observe the bacterial viability of the biofilm on the sample, the biofilm was stained using the LIVE/DEAD BacLight Bacterial Viability Kit (Invitrogen, Eugene, OR, USA). The kit contains two fluorescent dyes: SYTO-9 green fluorescent dye and propidium iodide (PI) red fluorescent dye. In CLSM, fluorescent green and red dots represent live and dead cells, respectively. For staining, incubate 1 ml of a mixture containing 3 µl of SYTO-9 and 3 µl of PI solution at room temperature (23°C) in the dark for 20 minutes. After that, the stained samples were observed at two wavelengths (488 nm for live cells and 559 nm for dead cells) using a Nikon CLSM apparatus (C2 Plus, Nikon, Japan). Measure the biofilm thickness in 3-D scanning mode.
How to cite this article: Li, H. et al. Effect of Pseudomonas aeruginosa marine biofilm on microbial corrosion of 2707 super duplex stainless steel. science. House 6, 20190; doi:10.1038/srep20190 (2016).
Zanotto, F., Grassi, V., Balbo, A., Monticelli, C. & Zucchi, F. Stress corrosion cracking of LDX 2101 duplex stainless steel in chloride solutions in the presence of thiosulfate. corrosion. the science. 80, 205–212 (2014).
Kim, S.T., Jang, S.H., Lee, I.S. and Park, Y.S. Effect of solution heat treatment and nitrogen in shielding gas on the pitting corrosion resistance of super duplex stainless steel welds. corrosion. the science. 53, 1939–1947 (2011).
Shi, X., Avchi, R., Geyser, M. and Lewandowski, Z. A chemical comparative study of microbial and electrochemical pitting in 316L stainless steel. corrosion. the science. 45, 2577–2595 (2003).
Luo H., Dong K.F., Li H.G. and Xiao K. Electrochemical behavior of 2205 duplex stainless steel in alkaline solutions at various pH values ​​in the presence of chloride. electrochemistry. Journal. 64, 211–220 (2012).