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.     

Influence of Cl- and polarization potential on crevice corrosion behavior of X70 pipeline steel北大核心CSCD

The crevice corrosion behavior of X70 pipeline steel in NaHCO3 solution with varying Cl- concentration was investigated by potentiostatic polarization method in terms of the initiation and development of crevice corrosion. Results show that inside the crevice the X70 steel could suffer from localized corrosion in NaHCO3 solution by polarization potential-0.4 V. The acidification initiated firstly at the crevice mouth and then extended gradually to the bottom. The hydrogen evolution could be observed with the development of corrosion and acidification. The cathodic reaction changed from the reduction of the dissolved oxygen to the reduction of hydrogen ions. The presence of Cl- did not change the crevice corrosion mechanism. With the increase of Cl- concentration, however, the crevice corrosion rate increased. The corrosion region moved towards the crevice bottom gradually and then pitting corrosion occurred with the increasing polarization potential. The initiation of crevice corrosion was determined by the polarization potential. © 2016, Corrosion Science and Protection Technology. All rights reserved.     

Conditions for stress corrosion cracking to occur from crevice corrosion sites and related electrochemical features

The occurrence of stress corrosion cracking (SCC) from crevice corrosion sites was studied using a kind of occluded U‐bend specimen of Type 316L (UNS S31603) stainless steel. It was done in 0.5 M NaCl solution at room temperature and 50°C. The galvanostatic and potentiostatic polarization methods were adopted. It was found that a tight crevice and high polarization current were the necessary conditions for SCC to occur relative rapidly from crevice corrosion sites. Meanwhile, if there was obvious SCC developing from a crevice corrosion site, the IR drop (or solution resistance) in the crevice path would increase. The increase of IR was attributed to the corrosion product deposition and/or hydrogen bubbles evolved from the cracks. On the other hand, the usually high aspect ratio of stress corrosion cracks, i.e. the inhibited dissolution on the crack walls, might be explained as due to the existence of high IR drops in them.     

409型不锈钢在冷凝液中的缝隙腐蚀行为

运用冷凝液循环蒸发方法模拟汽车消声器内部腐蚀环境,对比研究了在有/无缝隙条件下409型不锈钢在冷凝液中的腐蚀行为。结果表明:与无缝隙试样相比,有缝隙试样在循环试验过程中表现出相对较低的自腐蚀电位;20次循环试验后,腐蚀阻力较低,腐蚀深度较大;缝隙导致不锈钢局部腐蚀速率约增大2.4倍,这主要是由缝隙内部在蒸发过程中更容易保持电解液腐蚀环境、并不断酸化导致的。     

Rainbow fringes around crevice corrosion formed on stainless steel AISI 316 after ennoblement in seawater

The crevice corrosion occurrence probability of stainless steel (SS) AISI 316 was increased under ennoblement condition due to chemically added H₂O₂ into seawater. The H₂O₂ was used to simulate the important factor causing ennoblement in natural marine biofilm. Morphology of the crevice corrosion was observed using an incident‐light source microscopy. Some interesting “rainbow” fringes were observed around micro‐crevices. The mechanism was discussed from the ions diffusion and potential distribution during the crevice formation. This result shows that under ennoblement condition the colored fringe is a distinct characteristic of the morphology of localized corrosion for stainless steel.     

The localized corrosion of Al 6XXX alloys

This paper presents some recent findings on localized corrosion with a focus on Al 6XXX alloys and on the current times resistance (IR) voltage that exists between the separated anodic and cat hodic reactions. Some newly developed concepts help quantify the relationship between the IR voltage and the polarization curve that exists on the crevice wall, thereby providing for a deeper understanding on how crevice corrosion occurs in many metals and alloys. A signature of the IR voltage form of crevice corrosion in metal/electrolyte systems is the existence of an active/passive transition in their polarization curves. An aluminum/electrolyte system has been found to undergo this form of crevice corrosion. Some new results on intergranular corrosion in Al 6XXX alloys are also presented. For more information, contact B.A. Shaw, The Pennsylvania State University, Department of Engineering Science and Mechanics, University Park, Pennsylvania 16802; (814) 865-7828; fax (814) 865-0122; e-mail bas13.psu.edu.     

Loch- und Spaltkorrosion von Chrom- und Chromnickelstählen in chloridhaltigen Lösungen

Pitting and crevice corrosion of stainless steels in chloride solutions In practice stainless steels in chloride containing waters are found to be susceptible to crevice corrosion and pitting. Corrosion tests were carried out on AISI 304 L stainless using a simulated crevice and the compositions of the electrolyte in the crevice determined. Long term potentiostatic tests were used to determine the critical potentials for crevice corrosion (U_S), for various steels in sodium chloride solutions at different concentrations and temperatures. The steels studied were 22 CrMo V 121, X 22 CrNi 17 and AISI 304 L. Like the critical pitting potential (U_L), U_S was found to have a strong dependence on the chloride content of the external solution. At higher concentrations the two potentials were similar. At lower concentrations the U_S was lower than U_L. The knowledge of these critical potentials together with well known rest potentials for a steel in an electrolyte of known concentration, allows conclusions to be drawn about its susceptibility to pitting and crevice corrosion. The method is suitable also for other passive metals.     

Effect of the Crevice Former on the Corrosion Behavior of 316L Stainless Steel in Chloride-Containing Synthetic Tap Water

To restrain the failure of the plate heat exchanger (PHE) in customer boiler working fluid, the effect of crevice former type on the corrosion behavior of the 316L stainless steel plate was investigated using electrochemical methods and surface analyses in chloride-containing synthetic tap water (60 °C). The localized corrosion under metal–metal crevice condition was initiated more easily than that under the metal-gasket crevice condition due to the restricted mass transport at the gasket crevice mouth. However, the anodic current under the metal–metal crevice condition was lower than that under metal-gasket crevice condition at a higher anodic potential, indicating that that the metal dissolution under EPDM crevice would be higher than that under metal crevice under the accelerated corrosion condition. Because narrow crevice gap that was formed under gasket accelerated the anodic dissolution at the crevice mouth, the perforation tendency under metal-gasket crevice condition is much higher than that under metal–metal crevice condition. As a result, the crevice geometry, especially the crevice gap, mainly affected the corrosion behavior of PHE material.     

Predicting the chemistry,corrosion potential and corrosion rate in a crevice formed between substrate steel and a disbonded permeable coating with a mouth

A model developed in an earlier work was used in this work to investigate the effect of coating permeability on the evolution of solution chemistry, corrosion potential, and rate in a crevice formed between a steel surface and a coating disbonded from it. The crevice gap varies along distance from the mouth, and the coating is permeable to ions and/or oxygen (O₂). The earlier work focused specifically on modeling the effect of variable gap (on crevice corrosion) with the coating impermeable to either ions or O₂. In both works, the crevice chemistry was an aerated, diluted sodium chloride solution, which at the mouth was set to be different from that initially in the crevice. The results of this work show that a permeable coating behaves like a membrane, which, under a cathodic polarization at the crevice mouth, tends to raise the in-crevice sodium ion concentration and pH more rapidly relative to an impermeable coating. Later, as the sodium ion concentration and pH in the crevice become greater than at the mouth, the permeable coating tends to reverse the transport direction for ions. At a mouth potential of ?0.900 V vs. saturated Cu/CuSO₄, the cathodic current is sufficient to suppress all O₂ penetrating the crevice both from the mouth and through the coating. The practical implication is that in the presence of sufficient cathodic polarization, a permeable coating, when disbonded, can still be capable of protecting the substrate steel from corrosion attack.     

Ability of acoustic emission technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel

This experimental work was aimed at investigating the ability of acoustic emission (AE) technique for detection and monitoring of crevice corrosion on 304L austenitic stainless steel. Crevice initiation, propagation and repassivation was controlled by additions of hydrogen peroxide and hydrochloric acid and by the extent of the applied torque of crevice assembly, in the presence of chloride ions. The simultaneous measurements of corrosion potential of the specimen and AE global activity during the test, as well as the characterization of acoustic parameters of AE signals, evidences a good correlation between potential and AE activity fluctuations, AE rate and amplitude of crevice damage in terms of weight loss and metallic surface affected, in each tested experimental condition. Moreover, the evolution of cumulative% of AE signals number versus selected acoustic parameters shows that rise time, counts number, duration and cumulative energy of AE signals are affected by crevice development. Finally, visualization of crevice initiation and propagation during the test allows to propose that bubbles formation from cathodic reactions within the crevice is the emissive mechanism.     

Miniaturisierte elektrochemische Sensoren zur in-situ-Untersuchung der Spaltkorrosion in Modellsystemen

In-situ-investigation of crevice corrosion in model systems using miniaturized electrochemical sensors Measuring characteristics of miniaturized sensors for the determination of the parameters pH value, oxygen content, concentration of chloride ions and redox potential was tested and optimized with regard to the application in model crevices. The sensors were used for examinations of crevice corrosion in 0.1 molar and 1 molar solution of NaCl at the following alloys: X 20 Cr 13, X 2 CrNi 18 10, X 2 CrNiMoN 17 13 5, X 2 CrNiMoN 17 13 5*, X 2 CrNiMo CuN 20 25 6. Corrosion characteristic of the alloys and the change of crevice electrolyte without external polarization and with galvanostatic polarization (i = 10 μA/cm², i = 200 μA/cm²) were tested and discussed by the hand of the model concepts from Oldfield and Sutton [1]. In experiments with galvanostatic polarization the steels with increasing content of chromium or molybdenum showed a growing stability against crevice corrosion. The results showed that simultaneous measurements of the above mentioned chemical parameters of crevice electrolyte in connection with the corrosion potential can supply additional information about causes and mechanism of crevice corrosion.     

Moiré based method for real‐time crevice corrosion monitoring

A novel real‐time technique was developed to monitor localized corrosion occurring over a metal surface. It is an optical method based on the Moiré technique that has undergone further improvements and fine tuning for more accurate measurements. Upon testing, good agreements were obtained with the microscopically determined penetration depth. Application for this technique was demonstrated through real‐time monitoring of crevice corrosion activity occurring on the surface of AISI 316 (UNS S31600) stainless steel immersed in 3% NaCl at 60 °C. The crevice was an artificial clear glass/metal crevice with a gap thickness of 5 μm. Based on the findings of these results it was shown that this method can effectively and accurately be used to monitor crevice corrosion.     

Influence of activated carbon on crevice corrosion in adsorption tower of advanced liquid processing system

ABSTRACT

The adsorption tower made of type 316L stainless steel (SS) in Multi-nuclide Removal Equipment (Advanced Liquid Processing System) which uses Ag-impregnated activated carbon (Ag AC) as an adsorbent experienced crevice corrosion. The influence of Ag AC on the crevice corrosion susceptibility and E_sp of 316L SS was investigated by performing electrochemical experiments. Crevice corrosion was observed in the specimen in contact with the Ag AC. On the other hand, there was no crevice corrosion without the Ag AC in both pH 7.4 and pH 12 solutions. Clear ennoblement of spontaneous potential (E_sp) by in contact with activated carbon was observed and that was clearly higher than the repassivation potential for crevice corrosion (E_R,CREV). Thus, the presence of the AC notably increased E_sp of 316L SS and this resulted in increased crevice corrosion susceptibility by the galvanic effect.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

Implications of internal cathodic reactions for crevice attack of stainless steels in chloride environments

Abstract

Modelling of the crevice chemistry in stainless steels in chloride environments at ambient temperatures has been conducted in order to evaluate the impact of internal cathodic reactions on the potential and pH within the crevice. Consideration of the internal cathodic reactions is of particular importance in predicting the behaviour of crevices formed between dissimilar metals. The model is based on mass conservation of species and incorporates a range of chemical and electrochemical reaction processes. Hydrogen ion reduction within the crevice has a marked effect on the time evolution of the pH in the crevice and consequently on predictions of the time to passivity breakdown based on the critical pH concept. The impact on the steady state pH depends on the corrosion potential and on crevice dimensions. In the latter context, decreasing the gap or increasing the length does not invariably create more severe conditions for passivity breakdown. There is an optimum magnitude of the dimensions for inducing crevice attack. Coupling the stainless steel to a more noble material within the crevice, when the main cathodic reaction is reduction of hydrogen ions, may be more likely to retard crevice attack by virtue of the higher crevice pH, provided that effective coupling of the materials in the external environment is constrained. A specific bulk conductivity exists below which the critical crevice chemistry does not develop, but this is associated with potential drop in the bulk solution rather than in the crevice.     

The crevice corrosion behaviour of stainless steel in sodium chloride solution

The crevice corrosion behaviour of 13Cr stainless steel in NaCl solution was investigated mainly by electrochemical noise measurements, considering the influences of the crevice opening dimension (a) and the area ratio of the electrode outside the crevice to the one inside the crevice (r). Results show that the increase of r value prolongs the incubation period of crevice corrosion, but crevice corrosion develops rapidly once the crevice corrosion occurs. The crevice corrosion develops preferentially at the crevice bottom and then spreads to the whole electrode surface. Proton could reduce on the uncorroded area and hydrogen bubbles form inside the crevice.     

CREVICE CORROSION BEHAVIOR OF THE STEEL X70 UNDER CATHODIC POLARIZATION

采用矩形缝隙装置, 测量了模拟剥离涂层下不同位置X70钢的电位、溶液pH值及氧含量随时间的变化曲线. 研究了外加阴极极化电位、涂层破损尺寸和缝隙厚度对X70钢在Na2SO4溶液中的缝隙腐蚀行为的影响. 结果表明, 缝隙内氧气迅速耗尽并使溶液pH值升高, 氧耗尽与外加阴极极化电位无关. 随着缝口阴极极化程度加大, 缝隙内各点电位负移, 有效保护距离增加. 溶液介质电位(IR)降集中在缝口. 极化程度过高会导致氢气的析出. 减小缝隙厚度和破损点尺寸使缝隙内极化程度降低.     

The nature of crevice corrosion of aluminum in chloride solutions

To study crevice corrosion of pure aluminum, polished specimens partly covered with a glass foil were polarized potentiostatically in 1 N NaCl-solution at potentials negative to the critical potential for stable pitting (pitting potential). For comparison, non-crevice experiments were performed on polycrystalline and singlecrystalline material in neutral as well as acidified 1 N NaCl-solution and in AlCl₃-solutions. Corrosion morphology was examined by scanning electron microscopy. In current-time plots recorded during experiments on crevice corrosion, both an incubation and a propagation stage are discernible. If experiments were interrupted during the induction period, micropits were found inside the crevice. This unstable micropitting is detectable down to 0.30 V below the pitting potential. In contrast, during crevice corrosion propagation, the aluminum surface undergoes general attack. In a range of 0.2 V below the pitting potential, dimpled surfaces are produced. At more negative potentials, metal dissolution occurs crystallographically oriented. An identical behaviour was detected on unshielded samples polarized in the same potential range in both 1 N AlCl₃- and acidified 1 N NaCl-solution. Hence, the build-up of an acidic electrolyte is considered the sufficient requirement for crevice corrosion initiation.     

Crevice corrosion of Q235 carbon steels in a solution of NaHCO3 and NaCl

The crevice corrosion of Q235 carbon steels in a solution of NaHCO₃ and NaCl was investigated mainly by electrochemical noise. Three stages of crevice corrosion were found and include an induction stage, a transformation stage and a stable development stage. Principal component analysis and hierarchical agglomerative cluster analysis were used to identify the crevice corrosion stages. The electrode area ratio of the outer to the inner part of the crevice (r) significantly influenced the occurrence and development of crevice corrosion. The induction stage time increased as r increased.     

Wasserstoffinduzierte Spannungsrißkorrosion an unverzinkten und verzinkten Baustählen

Hydrogen induced stress corrosion cracking of non galvanized and galvanized construction steels The processes of atmospheric corrosion and corrosion in collected water which may lead to hydrogen induced stress corrosion cracking of high-strength reinforcing steels in casing tubes before injection with concrete are discussed. Hydrogen uptake during corrosion occurs in weakly acid solutions as well as in neutral or alkaline aqueous solutions. The hydrogen uptake by proton discharge in acid solutions decreases with increasing pH of the electrolyte. Hydrogen can also be absorbed in neutral to weakly alkaline solutions if steels are plastically deformed and water reacts with the fresh iron surface. In alkaline solutions, hydrogen uptake is possible if, at the generally passivated steel surface, localized corrosion (pitting or crevice corrosion), local galvanic cells and a sufficient decrease in the pH of the pit electrolyte occurs. In the case of galvanized steels with damaged zinc layers, hydrogen uptake may result from the cathodic polarization of the free steel surface by zinc dissolution. The absorbed hydrogen interacts with the microstructure of the steels and weakens the bonds between the iron atoms. The influence of the microstructure of high-strength steels on the fracture behaviour is discussed on the basic of the so-called decohesion theory.     

Influence of the microstructure and alloying element on the polarization behaviour within the crevice of UNS S32304 duplex stainless steel

The influence of microstructure evolution and alloying element redistribution of UNS S32304 duplex stainless steel induced by annealing treatment on the crevice corrosion behaviour was studied. As the annealing temperature was increased from 1030 to 1150 °C, the crevice corrosion resistance was decreased and the active peaks were not only increased in magnitude but also shifted towards the more noble direction. Austenite and ferrite have greatly different polarization behaviour within the crevice. This study provides guidance to the material design and usage in industry field in consideration of different polarization behaviour induced by the evolution of microstructure and alloying elements.