Localized Corrosion Of Stainless Steel Research Articles

PREDICTION OF ELECTROCHEMICAL PROCESSES OF LOCAL DISSOLUTION OF STAINLESS STEELS. PART 1. SPECTRAL –FREQUENCY ANALYSIS OF POTENTIAL FLUCTUATIONS

The propagation of localized corrosion of stainless steels was investigated by spectral frequency analysis (HPA) of potential fluctuations in the modes of stationary and cyclic galvanostatic polarization. Corrosion-resistant austenitic and austenitic-ferritic chromium-nickel steels were studied: 12X18N10T, 10X17N13M2T, 08X22N6T, resistant to pitting corrosion, in an aqueous solution of 0.1 M NaCl with a cyanide-containing complexing agent, a corrosion stimulator - 0.01 g/l (K3[Fe(CN)6]). The studies were carried out in the range of low densities (0.5–10 µA /cm2) due to the small values of the limiting diffusion current density in oxygen. To find the time of the origin of macropittings, it is proposed to use the NAV of chronopotentiograms with their subsequent statistical processing (Fourier transform). It has been established that fluctuations in the boundary polarization regime are characteristic of the process of the origin, development and passivation of macropittings. In the mode of stationary galvanostatic polarization, frequency characteristics were studied in the range of 1.0 ± 0.5 µA/cm2. When analyzing spectral density graphs, it was found that the dominant frequency characterizes the time of formation of the macropitting, and the sections of the chronopotentiogram should be divided into sections with a duration of no more than 50-100 s. In non-stationary conditions of galvanostatic polarization in the range of 1.0-10 µA/cm2 in a cyclic mode, it was found that the processes of nucleation and passivation of macropittings can be traced with a changing value of the polarizing current. Based on the frequency range of chronopotentiograms, it was found that the average macropitting lifetime is 250-300 s (frequency range 0.033 - 0.004 Hz). The dominant frequencies are determined to identify the characteristic dependencies of the envelopes along the upper (fhg) and lower (fhg) boundaries of the potential change, based on them, an algorithm is proposed for selecting the values of the parameters of the prediction mode of the formation of macropitting processes.

Interaction of marine organisms on localized corrosion of 316L stainless steel in Dalian seawater

PurposeThe purpose of this paper is to study the interaction of main marine organisms on localized corrosion of 316L stainless steel in the Dalian Sea area.Design/methodology/approachThe steel plate was immersed in the Dalian Sea area for nine months to observe the biofouling and localized corrosion. The local potential distribution on the steel plate covered by marine organisms was measured. The local electrochemical measurements were performed to facilitate understanding the interfacial status under different biofouling conditions. The local surface morphologies and corrosion products were characterized.FindingsThe localized corrosion of stainless steel is mainly induced by the attachment of barnacles on the steel. The mussels have no influence on the localized corrosion. The cover of sea squirts could mitigate the localized corrosion induced by barnacles. Both crevice corrosion and pitting corrosion were found beneath the barnacle without the covering of sea squirts. The pitting damage was more serious than the crevice corrosion in the Dalian Sea area. The probing of sulfur element indicates that the potential growth of sulfate-reducing bacteria at barnacle center.Originality/valueThe above findings revealed that the interaction of marine organisms has significant influences on the localized corrosion of stainless steel. The influences of macro-fouling and micro-fouling on localized corrosion are discussed.

A study on localized corrosion behavior of 304 stainless steel in the presence of Allium Sativum extract inhibitor using electrochemical noise analysis

The present work aimed to investigate the Allium Sativum (garlic) extract as a localized corrosion inhibitor for AISI 304 stainless steel in hydrochloric acid medium. The Allium Sativum extract was characterized by FTIR and UV–visible spectroscopy. The corrosion resistance of the 304 stainless steel was studied using electrochemical noise (EN), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). According to the EN analysis, it was demonstrated that the addition of the inhibitor up to the optimum amount (8 cc L−1) increased the spectral noise resistance. The shot noise results illustrated that the distribution of the frequency of events shifts to a higher frequency region in the presence of Allium Sativum inhibitor, which is an indicator of less localized corrosion of stainless steel. Stochastic analysis for pit initiation and growth showed that although the pits initiation rate increased in the presence of the Allium Sativum extract because of its antioxidant nature, the formation of stable pits with a radius larger than 30 μm was significantly inhibited due to the filling of the metastable pits with phosphate compounds. Microscopic corrosion morphology confirmed the idea of the formation of phosphate compounds on the pits nuclei and re-passivation of the steel surface.

Effect of substrate on metallographic corrosion of cladding in stainless/carbon steel bimetal plate

The effect of substrate on metallographic corrosion of cladding in stainless/carbon steel bimetal plate is investigated in this paper. The metallographic observation results show that the presence of substrate (carbon steel) would lead to the over-corrosion of stainless steel grain boundary, interfering with the metallographic observation results of stainless steel.The over-corrosion of stainless steel grain boundary could be attributed to the iron ion released from carbon steel. The excessive iron ion would enlarge the difference of iron ion concentration between etchant and stainless steel grain boundary, forming the concentration cell. The concentration cell would promote the localized corrosion of stainless steel, aggravating the corrosion degree of stainless steel.

The effect of CeCl3 inhibitor on the localized corrosion of stainless steel in chloride solutions

AbstractStainless steels have been used extensively in many sectors such as medical and household appliances as well as construction. This has been primarily due to their high resistance to corrosion attacks, reasonable cost, and excellent mechanical properties. However, when placed in corrosive media stainless steel is susceptible to localized corrosion attacks, especially when placed in chloride solutions. The paper explores the issue of corrosion liability of austenitic (AISI 316) and duplex (UNS S32205) stainless steels in et aconditions of seawater environment as well as under the influence of an inhibitor in the same environmental conditions. The behavior of stainless steels was examined via electrochemical testing relying on DC and AC techniques, optical metallographic analysis, scanning electron microscopy, and X‐ray diffraction analysis. Duplex stainless steel showed better resistance to localized corrosion but a higher tendency toward general corrosion in all examined solutions. Cerium chloride in a chloride solution showed inhibiting properties for both the AISI 316 and the UNS S32205.

A support vector machine‐based ensemble algorithm for pitting corrosion modeling of EN 1.4404 stainless steel in sodium chloride solutions

The resistance to localized corrosion of stainless steel in sodium chloride solutions is evaluated at different conditions. The effects of chloride ion concentration, acidity, and temperature on pitting corrosion resistance are analyzed. In order to develop a model capable of predicting pitting corrosion behavior of EN 1.4404 by an automatic way, a support vector machine‐based ensemble algorithm is proposed. An additional step related to feature selection is included in the model in order to improve the prediction capability. According to the excellent prediction results, the support vector machines (SVM) model is used to perform a sensitivity analysis for the purpose of analyzing the influence of the environmental variables on the breakdown potential and the pitting corrosion status modeling of this grade of stainless steel. Based on this analysis, it can be concluded that the breakdown potential is the main variable to be considered in pitting corrosion modeling whereas temperature is the most important one for breakdown potential modeling.

EIS Study on Effects of Inorganic Inhibitors on Localized Corrosion on Stainless Steels at PEFC Environments

Stainless steel is considered as a suitable material of PEFC metal separator because it has good durability, formability, chemical stability and reasonable price. Whereas, localized corrosion would occur on stainless steel due to potential and temperature change during PEFC operation because a metal separator contacts with acidic solution containing fluoride and chloride ions. It is generally known that a few percent of molybdenum as an alloy element inhibits localized corrosion. Hashimoto et. al. 1) proposed that dissolved molybdenum from stainless steel affected protection of steel surface. In previous study2), we discussed anti-corrosive effects of molybdate ions as an inhibitor in solution. In present study, we investigate inhibitor mechanisms of sodium molybdate, sodium tungstate and sodium phosphate for localized corrosion of stainless steel by electrochemical impedance spectroscopy. In this study, measurement of polarization curve and electrochemical impedance were conducted by three electrode methods. The working electrode was S44700 (Surface area : 0.28 cm2). The counter electrode was platinum wire and the reference electrode was a saturated KCl/Ag/AgCl (SSE) electrode. The electrolyte solution simulating PEFC operation environment (PEFC simulating solution) was 1 mol/dm3 H2SO4 aqueous solution (pH 3) which contained 10 ppm NaCl and 30 ppm NaF. Furthermore, some inorganic inhibitors were added to PEFC simulating solution as follows: 1 mmol/dm3 sodium molybdate, sodium tungstate or sodium phosphate. Polarization curves were measured by scanning the working electrode potential at 100 mV min-1 from open circuit potential to 1.5 V vs. SSE. Impedance measurements were carried out at potentials in passive and transpassive regions. Imposed AC potential amplitude was 10 mV and frequency ranges were from 10 mHz to 10 kHz. Figure 1 presents polarization curve and impedance spectra of S44700 in PEFC simulating solution. The polarization curve is composed of passive region from open circuit potential to 0.8 V vs. SSE and transpassive region from 0.8 V to 1.5 V vs. SSE. Impedance spectra show blocking behavior at passive region (0.7 V, 0.8 V vs. SSE) and inductive loops at transpassive regions (0.9 V, 1.0 V vs. SSE). In present study, we investigate inorganic inhibitors reducing transpassive dissolution current. Then, we propose inhibitor mechanisms of sodium molybdate, sodium tungstate and sodium phosphate by EIS. References 1) K. Hashimoto, K. Asami, M. Naka and T. Masumoto, Corros. Sci., 19, 857 (1979). 2) M. Ueyama, C. Tsukioka, Y. Hoshi, I. Shitanda, M. Itagaki, S. Takata, and T. Kogure, C01 – 697, 232 nd ECS Meeting. Figure 1

The role of titanium in the initiation of localized corrosion of stainless steel 444

Titanium has been added to ferritic stainless steels to combat the detrimental effects of intergranular corrosion. While this has proven to be a successful strategy, we have found that the resulting Ti-rich inclusions present on the surface play a significant role in the initiation of other forms of localized corrosion. Herein, we report the effect of these inclusions on the localized corrosion of a stainless steel using macro and micro electrochemical techniques. Through the use of scanning electrochemical microscopy, we observe the microgalvanic couple formed between the conductive inclusions and passivated metal matrix. The difference in local reactivity across the material’s surface was quantified using a 3D finite element model specifically built to respect the geometry of the corrosion-initiating features. Combined with electron microscopy and micro elemental analysis, localization of other alloying elements has been reported to provide new insight on their significance in localized corrosion resistance.

Macrofouling induced localized corrosion of stainless steel in Singapore seawater

Biofouling induced corrosion of stainless steels grades UNS S31603 and UNS S31254 was investigated at three sites off Singapore for 30months. No corrosion was observed on grade UNS S31254, while the propensity for corrosion by shellfish of UNS S31603 is ranked as oyster>>barnacles>>green mussels. Oysters caused extensive localised corrosion, penetrating 2mm thick plates with 12months with tracks of corrosion several centimetres long.Shallow crevice corrosion was observed under dead barnacles, with an explanation presented for why corrosion is more severe under dead barnacles than live ones. Green mussels did not cause any corrosion.

Influences of Chloride and Fluoride Ions on Localized Corrosion of Stainless Steels at Anodic Polarization

Polymer electrolyte fuel cells (PEFCs) are environmentally friendly generators and operate at relatively low temperatures, so they have been put into practical use as power sources for automobiles. A carbon plate is generally used for the separator of PEFC. However, there are problems in using carbon separator such as low mechanical strength and cost, thus metal separators are used for automotive PEFC. Stainless steels are considered to be suitable metal among several candidates for material of metal separator because it is highly corrosion resistant, high workable and relatively reasonable. Since the inside of the PEFC becomes particular corrosive environments, dissolution of metallic ions due to localized corrosion of stainless steel is feared. Typical conditions of the particular corrosive environments assumed in this research are as follows, chloride ion concentration: 10 ppm, fluoride ion concentration: 30 ppm, pH 3, electrode potential: 0.8 V vs. SSE, temperature: 80 degree centigrade. A schematic diagram of the anodic polarization curve of stainless steels is shown in Fig. 1. The anodic polarization curve is divided into three potential regions and they are defined as a passive region, a first transpassive region, and a second transpassive region. Anodic polarization curves of SUS 447 in three kinds of solutions are shown in Fig. 2. The following three solutions were used for measurements. A: pH 3 1 M H2SO4 (80℃) without halide ions, B: 1 M H2SO4 containing 10 ppm NaCl, C: 1 M H2SO4 containing 30 ppm NaF. The anodic polarization curve of SUS 447 in solution A without halide ion shows the passive region and the second transpassive region at nobler potential than 1.2 V vs. SSE. The anodic polarization curve of SUS 447 in the solution B containing chloride ions shows the first transpassive region and the current increase above 0.8 V vs. SSE is observed. If the potential of the PEFC cathode is assumed to be 0.7 ~ 0.8 V vs. SSE, it is near the boundary between the passive region and the first transpassive region, and metallic ions dissolution may occur. Furthermore, in the anodic polarization curve in SUS447 in a solution C containing fluoride ions, the current value in the first second transpassive regions is much larger than that in the solution B, indicating the acceleration of the dissolution rate. It is considered that corrosion protections such as surface treatment and inhibitor addition are necessary when stainless steels are used in the particular corrosive environment in PEFC. In this study, we investigated the influences of chloride and fluoride ions on localized corrosion of stainless steel by electrochemical measurements, and discuss the corrosion protection method of stainless steel as a metal separator of PEFC. Figure 1

(Invited) Passivity and Localized Corrosion of Stainless Steels in Energy-Related Applications

In recent years, new types of environments related to energy technologies can provide new challenges for the passivity of traditional materials. Examples are different types of biofuels (ethanol, ethanol-gasoline blends, biodiesel). For instance, stress-corrosion cracking of steels can take place in ethanolic environments and Al alloys can show very fast degradation in ethanol-containing fuels at higher temperatures. This presentation will focus on passivity and localized corrosion of stainless steels in such new type of environments. Critical factors of localized corrosion were studied in different ethanol-gasoline blends, in presence of various corrosion-enhancing factors (such as H2O, chloride contamination). The influence of the different factors on occurrence of pitting corrosion and the morphology of growing pits was studied. In addition, XPS measurements were carried out, to explore the effect of the specific environment on the nature of the passive films. Other examples of the behavior of stainless steels in energy-related applications will be shortly discussed, such as passivity and localized corrosion in molten salts that can be used as heat transfer media in high temperarature applications.

Transient analysis through Hilbert spectra of electrochemical noise signals for the identification of localized corrosion of stainless steel

Hilbert spectra allow identification of instantaneous frequencies that are attributed to specific corrosion mechanisms in electrochemical noise data. The present work proposes to identify and analyze areas of interest in Hilbert spectra, which enables to obtain valuable frequency information from electrochemical noise signals. Experiments were performed on AISI304 exposed to aqueous HCl solutions at different pH values resulting in either distinct general or localized attack. Results indicate that application of the proposed transient analysis to Hilbert spectra provides a significantly improved determination of the frequency characteristics of the electrochemical noise signals compared to time–frequency data analysis without transient analysis.

Probing the vertical profiles of potential in a thin layer of solution closed to electrode surface during localized corrosion of stainless steel

Based on a home-built integrated system of scanning reference electrode technique and scanning tunneling microscope (SRET/STM), a method for in situ measurement of vertical potential in the thin layer of solution closed to electrode surface during localized corrosion of stainless steel has been successfully established in this work. An obviously different vertical profile of potential over corrosion active sites and passive sites were firstly observed. The reason for this different was discussed taking into account the distribution of electric field and concentration of Fe3+/Fe2+ in a thin layer solution closed to electrode surface, due to the occurrence of localized corrosion.

Effect of biofilm on ennoblement and localized corrosion of stainless steel in fresh dam-water

AISI 304 stainless steel specimens were exposed in-situ to fresh dam-water for nearly 2 years. Open circuit potential (OCP) of the specimens becomes remarkably ennobled after exposure for about 40 days. The ennobled OCP of coupons is greatly affected by both immersion depth and sunlight. It is found that ammonium, nitrate, nitrite and chloride ions are enriched in the biofilm. It is suggested that the reduction of nitrate may be partly responsible for the OCP ennoblement. Localized corrosions at welds and crevices of specimens are attributed to both the OCP ennoblement of specimens and the chloride ion enrichment in the biofilm.

In situ characterization of localized corrosion of stainless steel by scanning electrochemical microscope

Scanning electrochemical microscopy (SECM) area scan measurements have been performed to investigate the localized corrosion of type 304 stainless steel in neutral chloride solution. Variations in the Faradaic current measured at selected tip potential values can be related to changes in the local concentration and electrochemical activities of electroactive species involved in corrosion reactions occurring at the substrate as a function of immersion times of the substrate and polarized currents or potentials applied on the substrate. To further verify the results acquired from cyclic voltammetric experiments, SECM measurements were employed to in situ study the compositions and electrochemical activity distribution profile of the pitting corrosion products of stainless steel. It has been demonstrated that the combination of feedback current mode with generation-collection (G-C) mode of SECM is suitable to elucidate the possible reaction mechanisms and paths involved in the localize corrosion of stainless steel in neutral chloride solution.

Role of Methanol on Pitting of Type 316 Stainless Steel

Abstract This work is aimed at improving the understanding of the localized corrosion of stainless steel in methanolic solutions. Potentiodynamic polarization curves on Type 316 (UNS S31600) were measured in methanol (CH3OH)-water (H2O)-1 M lithium chloride (LiCl) at water concentrations ranging from 1 wt% to 100 wt%. The pitting potential increased from 350 mV vs. saturated calomel electrode (SCE) to −100 mVSCE as the concentration of water increased from 0 wt% to 99 wt%. Dissolution kinetics were determined as a function of water concentration, from 100 wt% to 10 wt%, in a saturated pit environment. The overvoltage for active dissolution increased with decreasing water (increasing methanol) content. This, however, does not explain the decrease in pitting potential with increasing methanol content. Repassivation transients were determined by pulsing the potential to −150 mVSCE at different concentrations of water. The time to repassivate increased with decreasing water content, suggesting that the critic...

Unified approach to localized and general corrosion of stainless steels

Localized and general corrosion of stainless steels is considered. In the case of localized corrosion, statistical parameters are deduced from the comparison of the distributions of breakdown and corrosion potential values to rank different materials, environments and designs. Cumulative frequency F is considered for breakdown ( E b) and corrosion ( E c) potential, and both are represented on a logarithm plot as E= E(log F). An extrapolated value of F (the risk H) corresponding to E b= E c is related to the field behavior of the material. The risk H is formally related to the corrosion current density ( i) of the general corrosion approach. An analogy between the formalism of the probabilistic treatment of localized corrosion of stainless steels and that of uniform corrosion is highlighted through Monte Carlo simulation. Introducing a discretization model of the general corrosion, the time evolution of the surface roughness during general corrosion of stainless steels is reproduced in agreement with the experimental results. According to this model, the general corrosion can be treated on a similar basis of the localized corrosion in terms of discretization of corroding areas, and vice-versa localized corrosion can be treated on a similar basis of the general corrosion in terms of statistical distributions of the potential values.

Discretization Model of General Corrosion

Abstract An analogy between the formalism of a probabilistic approach to localized corrosion of stainless steels and the formalism of the classical approach to general corrosion of metals is highlighted. This formal analogy is justified experimentally through the study of the roughness evolution of stainless steels, iron, and zinc, corroded in sulfuric acid (H2SO4). A discretization model of general corrosion, based on a stochastic distribution of localized active areas on the surface, is proposed. Based on this model, a computer simulation is carried out to analyze roughness evolution and the role played by the active areas. Observations on the dissolution mechanism of a zinc monocrystalline sample according to the model also are reported.

Influence of temperature on the localized corrosion of stainless steels

Localized corrosion processes of passive metals are almost always initiated at local heterogeneities of the substrate material. In the case of stainless steels MnS inclusions are of primary importance. Increasing the temperature strongly accelerates the pitting. Detailed large-scale and microelectrochemical investigations show that this is mainly caused by an enhanced anodic dissolution facilitating stable pit growth and retarding repassivation. Activation of new inclusions, remaining inactive at lower temperature, may also occur but are of minor importance.

Detection of localized corrosion of stainless steels by optical interferrometry

An optical corrosion meter has been developed for materials testing and evaluation of different corrosion phenomena. The meter was based on principles of 3D holographic interferrometry for measuring microsurface dissolution, i.e. mass loss, and on those of electrochemistry for measuring the bulk electronic current, i.e. corrosion current of metallic samples in aqueous solutions. The early stage of pitting corrosion of UNS No. 304 stainless steel and crevice corrosion of UNS 316 stainless steel in natural seawater were monitored, in situ by the optical corrosion meter during the cyclic polarization tests. The observations of pitting corrosion were basically interferrometric perturbations detected on the surface of the UNS No. 304 stainless steel in seawater. In contrast, the observations of crevice corrosion were basically interferrometric perturbations detected on the surface of the UNS No. 316 stainless steel underneath a crevice assembly. Eventually, the interferrometric perturbations were interpreted as localized corrosion in the form of an early pitting or of an early crevice corrosion, of a depth ranging from 0.3 μm to several micrometers. Consequently, holographic interferrometry is shown to be a useful technique as a 3D-interferrometric microscope for monitoring pitting corrosion or crevice corrosion at the initiation stage of both phenomena for different metallic samples in aqueous solutions.