Initiation Of Crevice Corrosion Research Articles

Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625

Close packed coupled multi-electrodes arrays (MEA) simulating a planar electrode were used to measure the anodic current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel (UNS S31600) and Ni-Cr-Mo alloy 625 (UNS N06625). Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCl at 50{degree sign}C was found to readily initiate close to the crevice mouth (i.e., xcrit ≈ 0) at modest applied potentials (e.g., 0 VSCE) and to spread inwards and outside the crevice with time. In the case of alloy 625, crevice corrosion initiates further inside the crevice (i.e., xcrit is large) and requires higher applied potential (e.g., 0.05 VSCE). The local crevice current density increased dramatically over a short period to reach a limiting value in both cases.

The Effect of Anions on the Passive Film Properties and Localized Corrosion Behavior of Alloy C-22

This paper investigates corrosion behavior of Alloy C-22 in hot concentrated brines. The passive film behavior and localized corrosion properties of alloy C-22 as a function of nitrate and sulfate anions in concentrated chloride brines was investigated. Cyclic potentiodynamic polarization tests were used to study the general corrosion behavior of the alloy, Electrochemical Impedance Spectroscopy (EIS) and Mott-Schottky (M-S) were used to examine the electronic properties of the passive films, and constant potential tests were done to study crevice corrosion initiation, propagation and stifling of the alloy. The aim was to investigate the correlation between the electronic properties of the alloy's passive film and the localized corrosion susceptibility of the alloy. The results showed that anions had major impact on the repair- repassivation behavior but did not cause significant effect on the properties of passive film when it was intact.

Coupled Multielectrode Investigation of Crevice Corrosion of AISI 316 Stainless Steel

Close packed coupled multielectrode arrays simulating a planar electrode were used to measure the current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel. Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCI at 50°C was found to initiate close to the crevice mouth and to spread inward and outward with time. The local crevice current density increased dramatically over a short period to reach a limiting value.

An electrochemical evaluation on the crevice corrosion of 430 stainless steel by micro capillary tubing method

The aim of this study was to investigate the initiation of crevice corrosion for ferritic 430 stainless steel in artificial crevice electrode cells using the IR drop mechanism. The 430 stainless steel artificial crevice electrodes were potentiodynamically polarized in solutions of sodium chloride with different concentrations. The potentiostatic polarization was measured for various artificial crevice sizes by measuring the potentials in the crevice by the depth profile technique using a micro capillary tube which was inserted into the crevice. The criterion for IR>Δ Φ*, where Δ Φ* is the difference between the applied potential, ESURF, and the electrode potential of the active/passive transition, EA/P, was also measured during the process of crevice corrosion. The potentials in the crevice were successfully measured from −220 mV versus SCE to −360 mV versus SCE, which is lower than that of the external surface potential of −200 mV versus SCE. Thus these results show that evaluation of corrosion using the IR drop mechanism in the crevice was more objective and easier to reproduce than the existing methods.

Electrochemical evaluation of crevice corrosion of 430 ferritic stainless steel using the microcapillary tube technique

The aim of this study was to investigate the initiation of crevice corrosion for ferritic 430 stainless steel in artificial crevice electrode cells using the IR drop mechanism. The 430 stainless steel artificial crevice electrodes were potentiodynamically polarized in solutions of sodium chloride with different concentrations. The potentiostatic polarization was measured for various artificial crevice sizes by measuring the potentials in the crevice by the depth profile technique using a microcapillary tube which was inserted into the crevice. The criterion for IR>ΔΦ* , where ΔΦ* is the difference between the applied potential, E SURF, and the electrode potential of the active/passive transition, E A/P, was also measured during the process of crevice corrosion. The potentials in the crevice were successfully measured from −220 mV vs. SCE to −360 mV vs. SCE, which is lower than that of the external surface potential of −200 mV vs. SCE. Thus, these results show that evaluation of corrosion using the IR drop mechanism in the crevice was more objective and easier to reproduce than other existing methods.

Stainless steel crevice corrosion testing in natural and synthetic seawater

AbstractSusceptibility of stainless steel to crevice corrosion in natural and synthetic seawater was investigated by a new test method, developed by a research group, CrevCorr, of the Marine Working Party of the European Federation of Corrosion. The method was defined on the basis of a Round Robin test performed by twenty laboratories over the world [1, 2]. Among them was our Institute at the Adriatic coast. Geometry of the crevice model, gasket materials, finishing of metal surface and the electrochemical potential increase rate were strictly defined. The monitoring of the free corrosion potential of two austenitic steels and a duplex steel, in the constant flowing conditions, as well as the redox potential, temperature, chloride and oxygen content, have been carried out during six months in the natural seawater from the Adriatic Sea at the location in Dubrovnik, Croatia. Sharp drop of the corrosion potential was used as an indication of the crevice corrosion initiation. After exposure to the seawater eventual crevice damage on a steel specimen was detected by visual and microscopic inspections.In the synthetic seawater the organic component was simulated by glucose and glucose oxidase [3, 4]. The monitoring of the free corrosion potential and the redox potential was performed at 20, 30 and 40°C during five days, and results compared with those obtained in the natural seawater at same temperatures.

Effect of Ionic Interactions on the Initiation of Crevice Corrosion in Passive Metals

In the crevice corrosion process, oxygen reduction occurs faster than diffusion into an occluded crevice, causing deoxygenation of the crevice solution. Once oxygen is depleted in the crevice, oxygen reduction can only occur on the metal surface outside of the crevice. The cations produced by metal dissolution are hydrolyzed, which causes the pH of the crevice solution to drop. This increases the rate of metal dissolution, forming an autocatalytic coupling that causes concentrated electrolyte solutions to form in the crevice. The focus of this paper is the prediction of the effect of nonideal solution behavior on crevice corrosion using the ionic interaction model of Pitzer coupled with an electrolyte mass-transport model. This mathematical model was used to simulate the type 304 stainless steel crevice corrosion experiment of Alavi and Cottis. The results are in excellent agreement with experimental observations. The model was then applied to simulate the crevice corrosion initiation period of a titanium crevice. Comparison of the predictions to those generated via an ideal solution crevice corrosion model indicates that interionic forces draw chloride ions into the crevice and hinder the transport of hydrogen ions out of the crevice. © 2005 The Electrochemical Society. All rights reserved.

A Study on the Crevice Corrosion for Ferritic Stainless Steel by Micro Capillary Tube Method

The aim of this study is to investigate the initiation and propagation of crevice corrosion for ferritic stainless steel in artificial crevice based on micro capillary tube method. The 430 stainless steel in artificial crevice is potentiostatically polarized in different sodium chloride solutions. Potentiodynamic and potentiostatic polarization data were measured in situ. The potentials in the crevice were measured by depth profile using the 0.04 mm diameter micro capillary tube inserted in the crevice. The potentials in the crevice ranged from -220 mV to -360 mV vs SCE from opening to bottom of crevice, which are lower than the external surface potential, -200 mV vs SCE. Such a potential drop induced the change of the metal surface state from passive to active. The surface of metal is located in passive state in -200 mV but the inner surface keeps active state below -220 mV, Thus these results show that the It drop mechanism in the crevice was more objective for evaluation and the method was easier to reproduce. Therefore the potential drop is one of the reasons for crevice corrosion by measuring the potentials in narrow crevice with a new micro measuring system.

Initiation and repassivation of crevice corrosion of type 444 stainless steel in chloride solution

Effects of chloride ion concentrations, solution temperature, and crevice-forming materials on the crevice corrosion of type 444 stainless steel were investigated using a potentiostatic method. Critical crevice potential (Ecrev) and repassivation potential (Er) of the creviced alloy decreased with an increase in chloride concentration [Cl−], satisfying the logarithmic relationship between E and [Cl−]. In addition, Ecrev and Er of the alloy with silicone crevice former were measured to be higher than those of the alloy with an EPDM (Ethylene Propylene Diene Monomer) crevice former, suggesting that silicone was more effective in preventing water from penetrating crevices between a stainless steel sheet and the crevice former. In electrochemical current transient measurements with an applied potential, the intensity of current transients corresponding to the initiation of metastable pits increased abruptly near the Er of the alloy, indicating that the stability of crevice corrosion is associated with the initiation of metastable pits.

Effect of the Crevice Gap on the Initiation of Crevice Corrosion in Passive Metals

Abstract Past research into the mechanism governing the time to active crevice corrosion—the incubation period—of a passive metal crevice has produced theoretical models coupled with the B-dot model, the Debye-Huckel limiting law, and other activity models to correct for nonideal behavior at moderately high concentrations. In this research, the transport model of Watson and Postlethwaite is coupled with the ionic interaction model of Pitzer to predict the effect of the crevice gap on the iR drop and chemical activity of the crevice solution. Two cathodic reactions, crevice external oxygen reduction and crevice internal hydrogen ion reduction, are assumed to balance metal dissolution. To validate the model, the experimental Type 304 (UNS S30400) stainless steel crevice of Alavi and Cottis is simulated. Model predictions improve upon predictions of past models and match observations of this experimental work within experimental uncertainty. The effect of crevice gap on a titanium crevice immersed in 0.5 M a...

Initiation and propagation of pitting and crevice corrosion of hydrogen-containing passive films on X70 micro-alloyed steel

Hydrogen promoted initiation and propagation of pitting and crevice corrosion of X70 micro-alloyed steel were characterized by potential dynamic measurements, the scanning reference electrode technique (SRET) and electrochemical impedance spectra (EIS). At open circuit potential, in situ SRET results show that hydrogen accelerates the nucleation and propagation of pitting of X70 steel. The pitting potential E p of X70 steel gradually decreases with an increase of chloride ion concentration in NaHCO 3 solution. Pre-charged hydrogen does not have a significant effect on the pitting potential E p and open circuit potential E corr of the steel in 0.5 M NaHCO 3 solution. However, a synergistic effect of hydrogen and Cl − on the anodic dissolution and pitting potential of X70 steel is observed in 0.5 M NaHCO 3 solution containing chloride ions. When crevices are present in X70 steel, hydrogen accelerates the initiation and progress of crevice corrosion. The mechanisms by which hydrogen promotes the initiation and propagation of pitting and crevice corrosion are proposed and discussed.

Micro Capillary Tube 방법을 이용한 430 스테인레스강 틈의 폭변화에 따른 틈부식의 전기화학적 평가

본 연구는 전기화학적 실험측정으로 페라이트계 430스테인레스강 시험편에 인위적으로 틈을 형성시켰다. 부식용액은 IN <TEX>$H_2SO_4+0.1N\;NaCl$</TEX> 전해액을 사용하였고, 각 시험편의 틈의 크기를 달리하였다. 전기화학적 평가방법은 -600mV/5CE에서 정방향으로 +1,200mV/SCE까지 주사속도 600mV/hr로 동전위 분극시험을 실시하여 부식전위, 부동태 전류밀도 등의 부식거동을 분석하였다. 그리고 정전위 분극시험을 실시하여 부동태 구간 전위 -200mV/SCE를 일정하게 인가 한 후, 틈내에 부동태 전류밀도와 틈부식 발생시간을 계측하였다 실험방법에 있어 Microcapillary tube(MCT)를 이용한 방법으로 틈내 각 지점의 전위를 틈 깊이에 따른 틈내부의 전위강하(IR Drop)에 주목하고, 575 430 스테인레스강 금속에 대한 분극특성과 연계하므로써 틈부식의 발생 원인을 '전위의 이동'의 관점에서 규명 하였다. In this study, the IR drop theory was adopted to explain the initiation of crevice corrosion in the framework of IR drop in crevice electrolyte. Furthermore, the electrochemical polarization was measured to study the mechanism of crevice corrosion for type STS430 stainless steel. lest method adopts under condition that the size of specimen is <TEX>$10\times20\times5mm,\;in\;1N\;H_2SO_4+0.1N\;NaCl$</TEX> solution, and the artificial crevice gap sizes are three kinds, the Micro capillary tube size is inner diameter 0.04 mm, outer diameter 0.08 mm. Crevice corrosion is measured under the applied voltage of passivation potential -200mV/SCE, resulted from anodic potentio-dynamic polarization to the external surface along the crevice. The potential difference was measured by depth profile by Micro capillary tube which inserted in the crevice. The obtained results of this study showed that 1) As artificial crevice gap size became narrow, the current density was increased, whereas no crevice corrosion was found in the crevice gap size <TEX>$3\times0.5\times16mm\;in\;1N\;H_2SO_4+0.1N\;NaCl\;solution\;at\;20^{\circ}C$</TEX> 2) potential of the crevice was about from -220 to -358mV which is lower than that of external surface potential of -200mV The results so far confirmes that the potential drop(so-called IR drop) in the crevice is one of the major mechanisms the process of crevice corrosion for 430 stainless steel.

Crevice Corrosion of Alloy 625 in Natural Seawater

Abstract An experimental study was conducted to determine the influence of temperature on crevice corrosion initiation for Alloy 625 (UNS N06625) in natural seawater. These tests showed that there was a critical potential-temperature-time relationship needed to initiate crevice corrosion. The potential necessary to cause crevice corrosion on Alloy 625 decreased (became less noble) when the temperature was increased from ambient to 40°C. The crevice initiation potential decreased from 300 mV for ambient temperature seawater to 100 mV for 40°C seawater. Crevice initiation potentials were essentially unchanged between 40°C and 65°C, while the time required to initiate crevice corrosion decreased as temperature increased. In a second aspect of this work, natural seawater exposure studies were conducted to determine if there is a mechanistic connection between ennoblement (the gradual elevation of corrosion potential that occurs during long-term continuous immersion in natural seawater) and crevice corrosion i...

Temperature Dependence of Crevice Corrosion Initiation on Titanium Grade-2

The temperature dependence of crevice corrosion initiation on titanium grade-2 has been investigated using a galvanic coupling technique. The film breakdown/repassivation transients indicate a temperature threshold, around 65°C, for the initiation of crevice corrosion. The number, size, frequency, and background current of these events increased when the temperature was increased from 65 to 80°C. Analysis of single transients suggests that the temperature also has an effect on the repassivation mechanism. Image analysis of corroded coupons reveals that crevice initiation and deeper penetration occur around the edge of the creviced area. Surface studies using electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy show oxide film flaws accompanied by water incorporation at temperatures above the 65°C threshold. Under creviced conditions, the occurrence of film flaws is the key process leading to the development of acidity and the initiation of crevice corrosion. © 2002 The Electrochemical Society. All rights reserved.

Experimental procedure for crevice corrosion studies of Ni–Cr–Mo alloys in natural seawater

An experimental procedure intended for crevice corrosion studies on Ni–Cr–Mo alloys is demonstrated. In this procedure a potentiostatic control of crevice corrosion specimens is applied to an immersible crevice cell design that uses a fluoroelastomer gasket crevice former. The procedure is demonstrated for a crevice susceptibility study on Alloy 625 in elevated temperature natural seawater, where crevice corrosion initiation and propagation are shown to be influenced by the electrochemical potential. Potentiostatic current monitoring establishes the crevice initiation time and rate of propagation, while post-mortem inspections confirm the extent of crevice damage.

A study on the modeling of parameters affecting the Ir drop mechanism in the initiation stage of crevice corrosion

The sizable potential difference between the crevice mouth and the crevice tip is difficult to explain from theories mainly based on the chemical changes in crevice solution. In this study, the IR drop theory was adopted to explain the initiation of crevice corrosion in the framework of IR drop in the crevice electrolyte. Furthermore, the parameters linking the two components of potential drop — one due to accumulated charges from chemical changes of ionic species by mass transfer and the physical one caused by the current path through the crevice electrolyte — are examined. The mathematical model is constructed and the IR drop in the crevice is calculated using the FVM method. The chemical composition change in the crevice solution can affect the IR drop behavior through the intermediate parameter form of ion conductivity and viscosity, etc., together with the potential difference generated by the electric charge of locally charged ions. Viewed in this light, it can be concluded that the initiation mechanism only by IR drop is insufficient to explain the initiation of crevice corrosion in stainless steels that have very strong passivity.

Crevice Corrosion Studies Using Electrochemical Noise Measurements and a Scanning Electrode Technique

The formation of crevice corrosion on type 304L stainless steel when immersed in 0.05 M ferric chloride solution has been used to investigate electrochemical potential noise measurements. The surface activity of the stainless steel was simultaneously studied using a scanning electrode technique to provide corroborating evidence of crevice corrosion. The spontaneous potential noise fluctuations were recorded in a freely corroding system with respect to a reference electrode. Power spectral densities calculated by fast Fourier transforms and a stochastic technique were used for the analysis of the time records, in order to reveal fundamental characteristics of the fluctuations resulting from the initiation and propagation of crevice corrosion. A stochastic analysis tool based on a Poisson process test has been developed and evaluated using data generated by computer simulation of both stochastic and deterministic processes, before applying the analysis technique to real corrosion processes. There appears to be agreement between the two analysis methods; both revealed the presence within the time series of stochastic and deterministic features. Using a combination of noise analysis techniques it was possible to obtain evidence of the different corrosion processes occurring on the 304L stainless steel which were metastable pitting, propagation and termination of localized corrosion events, and the development of crevice corrosion. © 2000 The Electrochemical Society. All rights reserved.

Initiation modeling of crevice corrosion in 316L stainless steels

An advanced mathematical model has been developed to evaluate transport processes and chemical reactions during the initiation stage of crevice corrosion. The model considers the time evolution of the solution chemistry and electrochemistry within crevices, and uses the method of finite elements to solve the complex set of mass-conservation equations describing the system. In order to produce a useful estimate of the time of the incubation period, the concept of CCS (critical crevice solution), which delineates the transition between the passive and active states, has been introduced. The most important factors in crevice corrosion are the crevice gap and the crevice depth, especially the ratio of depth/width, on which the initiation of crevice corrosion reacts most sensitively. The potential drop inside the crevice consists of two components, the chemical potential drop and the physical potential drop, and the ratio of these components seems to be related to the crevice geometry. The results of numerical simulation of 316L (Fe–Cr–Ni–Mo alloy) show that the incubation time of the crevice corrosion is strongly dependent on the depth/width ratio of the crevice geometry.

Calculating chemical concentrations during the initiation of crevice corrosion

Numerical simulations of solution chemistry and electrochemical potential variations within crevice corrosion sites on stainless steel have been carried out using a method recently developed by Friedly and Rubin. Potential differences in the crevice solution have been calculated via the Nernst–Planck equation rather than by making the usual assumption of electroneutrality at any point, although this assumption is proven to be justified for time scales of >10 −13 s. Results of these simulations have been compared with the experimental data of Alavi and Cottis and the modelling results reported by Sharland. It is shown that typical passive current densities for stainless steels in near-neutral solutions are too low to induce local chemistry, or potential, changes capable of causing depassivation in the crevice. However, once active corrosion has been initiated, physically reasonable anodic current densities can be used to match model simulations with experiment. The precipitation of Cr(OH) 3 is the critical reaction responsible for reducing pH within the crevice, and consideration of the effect of potential on anodic current density allows the model to reproduce a minimum in the pH profile along the crevice, as found experimentally.

Heterogeneous phase equilibria as a basis for crevice corrosion modelling

The presented crevice corrosion model is intended to provide basic understanding of formation and dissolution of passivating layers during time dependent metal dissolution in an already deoxygenated crevice. It operates along a constant cathodic polarization curve in subsequent time steps with time dependent anodic polarization curves and corrosion currents. The anodic polarization curves are determined by dissoluted ionic chromium and respective Nernst potentials as well as by the mass of precipitated passivating chromiumhydroxide layers. All chemical reactions including diffusion of chloride into the model crevice configuration are assumed to be at equilibrium during the respective time steps. The amounts of passivating chromiumhydroxide masses are determined by lever‐rule application at increasing chromium and chloride contents in aquaeous solution of the quaternary water‐chromium‐hydrogen‐chloride phase diagram at various Nernst potentials. For this purpose, the established water–chromium Pourbaix diagram had to be redrawn in terms of ternary water‐chromium‐hydrogen phase diagrams for constant potentials. It was tentatively extended to the quaternary chloride including diagram based on literature results. This included solubility of chromiumchloride in hydrochloric acid and most probable effects of chloride ions on chromiumhydroxide solubility at saturation with chromium metal. The results of the interactive corrosion process are based on a crevice geometry drawn from previous publications and given initial solution concentrations as well as assumed polarization curves for time steps of one second. It is shown, how the process starts with concentration changes of chromium, chloride and hydrogen in the crevice, the subsequent formation of the passive layer and the corresponding decrease in the corrosion current and increase in the mixed potentials. In the presence of the chromiumhydroxide phase, however, chromium and hydrogen remain at low levels in the equilibrium aqaeous solution while chloride is increasing. The saturated solution reaches the four phase equilibrium concentration including saturation by chromium, chromiumhydroxide and chromiumchloride at corresponding Nernst potentials. The further increase in total chromium and chloride concentrations of the crevice then leads to initiation and propagation of crevice corrosion by formation of non‐passivating chromiumchloride at the expence and finally, the total dissolution of passivating chromiumhydroxide, at decreasing mixed potentials and increasing currents. Due to the low solubility of chromiumchloride in hydrochloric acid, the latter is finally formed with the result of the well‐known increase in crevice acidity. Thus, it is demonstrated that the acidification itself is not a requirement for crevice corrosion but rather a consequence of it.