Chloride-containing Environments Research Articles

Non-Destructive Electrochemical Testing for Stainless-Steel Components with Complex Geometry Using Innovative Gel Electrolytes

Corrosion can be a problem for stainless steels in chloride-containing or other aggressive environments, especially when they are formed as components with complex shapes. Monitoring the corrosion performance of the stainless steels during their in-service life is not always an easy task. Traditional electrochemical cells can be difficult to adapt to complex surfaces, and undesired crevices or liquid electrolyte leaks can occur. In the presented work, the possible use of non-destructive techniques with innovative gel electrolytes was investigated using portable cells. The electrolytes were based on agar (used as a gelling agent with ionic conductivity), glycerol (a plasticizer that improves adaptability to complex surfaces), and NaCl or KClO4 salts (which improve the conductivity and control the aggression of the tests). X-ray photoelectron spectroscopy (XPS) and Mott–Schottky analysis were carried out to obtain information about the influence of the electrolyte on the passive layer. The oxygen concentration and conductivity in the gels with various glycerol contents were compared to those in liquid electrolytes. Electrochemical impedance spectroscopy (EIS) measurements were carried out in liquids and gels. The performance of the gel cell on a stainless-steel component with a weld and complex shape was checked. The variation in the sensitivity of gels with and without chlorides to identify corrosion-susceptible regions was tested.

Understanding Fibre-Matrix Degradation of FRP Composites for Advanced Civil Engineering Applications: An Overview

Common concretes use considerable amounts of fresh water and river sand, and their excessive use is already seriously implicating the environment. In this respect, seawater and sea sand concrete (SWSSC) is a very attractive alternative, since it addresses the increasing shortage of fresh water and dredging of river sand. A major concern with reinforced SWSSC is the severe corrosion of the steel reinforcements by seawater (that has a very high content of chloride which is very corrosive), thereby seriously impairing the strength of such concrete. Fibre reinforced polymer (FRP) can be a suitable alternative to replace steels as reinforcement. However, there has been little systematic work to understand the degradation kinetics and mechanisms of FRP in the chloride-containing alkaline SWSSC environment. This review first provides an overview of the degradation of FRP composites in normal concrete and chloride-containing alkaline SWSSC environments, and then presents an example of a recent study using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) that may provide a pathway to systematic experimental approach to understanding such degradation. The review also makes a comprehensive assessment of the influence of environment-assisted degradation on mechanical properties of FRPs.

Corrosion-Induced Fatigue Failure of a First-Stage Flow Straightener Vane of an Aeroengine

One of the first-stage vanes of double-row flow straightener vane assembly (at seventh stage in the compressor) of an aeroengine was found broken from its root, during strip examination of the aeroengine. A metal piece was also collected from inside the engine. The flow straightener vane was said to have broken prematurely with respect to its total as-specified technical life. The broken vane, collected metal piece and a serviceable first-stage flow straightener vane were received for failure analysis. The result of the failure analysis is presented in this article. The vane failed due to fatigue, which was initiated from a corrosion pit on the pressure side near the leading edge of the vane. Chloride-containing environment led to the development of pitting, followed by pitting-induced fatigue cracking and final overload fracture. Chemical composition, microstructure and hardness evaluations indicated that the material of construction for the vane was the usual 12% Cr martensitic stainless steel nearly conforming to SUS 410J1, used in the hardened and tempered condition. The recovered metal piece from inside the engine was also made of martensitic steel with similar composition and microstructure to that of the failed and serviceable flow straightener vanes. The piece was badly rubbed and damaged resulting in cold deformation, evident from strain marks and an increase in hardness. All these findings support that it could be the broken aerofoil of the failed flow straightener vane.

An electroplated copper–silver alloy as antibacterial coating on stainless steel

Transfer and growth of pathogenic microorganisms must be prevented in many areas such as the clinical sector. One element of transfer is the adhesion of pathogens to different surfaces and the purpose of the present study was to develop and investigate the antibacterial efficacy of stainless steel electroplated with a copper-silver alloy with the aim of developing antibacterial surfaces for the medical and health care sector. The microstructural characterization showed a porous microstructure of electroplated copper-silver coating and a homogeneous alloy with presence of interstitial silver. The copper-silver alloy coating showed active corrosion behavior in chloride-containing environments. ICP-MS measurements revealed a selective and localized dissolution of copper ions in wet conditions due to its galvanic coupling with silver. No live bacteria adhered to the copper-silver surfaces when exposed to suspensions of S. aureus and E. coli at a level of 108 CFU/ml whereas 104 CFU/cm2 adhered after 24 h on the stainless steel controls. In addition, the Cu-Ag alloy caused a significant reduction of bacteria in the suspensions. The coating was superior in its antibacterial activity as compared to pure copper and silver electroplated surfaces. Therefore, the results showed that the electroplated copper-silver coating represents an effective and potentially economically feasible way of limiting surface spreading of pathogens.

Corrosion Resistance of Construction Steel in Conditions of Simultaneous Dynamic Loading and Chloride-Containing Corrosive Environment

AbstractCorrosion of steel reinforcement is the main focus of many studies on condition assessment of road infrastructure. The major uncertainty involves the behavior of steel rebar during dynamic ...

Time-dependent in situ measurement of atmospheric corrosion rates of duplex stainless steel wires

Corrosion rates of strained grade UNS S32202 (2202) and UNS S32205 (2205) duplex stainless steel wires have been measured, in situ, using time-lapse X-ray computed tomography. Exposures to chloride-containing (MgCl2) atmospheric environments at 50 °C (12–15 M Cl− and pH ~5) with different mechanical elastic and elastic/plastic loads were carried out over a period of 21 months. The corrosion rates for grade 2202 increased over time, showing selective dissolution with shallow corrosion sites, coalescing along the surface of the wire. Corrosion rates of grade 2205 decreased over time, showing both selective and pitting corrosion with more localised attack, growing preferentially in depth. The nucleation of stress corrosion cracking was observed in both wires.

Multi-state Markov modeling of pitting corrosion in stainless steel exposed to chloride-containing environment

Although stainless steels (SSs) have excellent general corrosion resistance, they are nevertheless susceptible to pitting corrosion. The variation of pit depth and density is significant for the prediction of likelihood of corrosion damage occurring in service. Among the available pitting corrosion models, it is difficult to identify a specific model capable of characterizing all the pit formation processes observed and one that can be used for estimating the evolution of pit density distribution with time. A physics-based multi-state Markov model giving a full description of pitting corrosion states is presented. The transition rates used in the model are determined by fitting the model to experimental data. The variation of pit depth and density is simulated. The simulation is verified by experimental scenarios of SS exposed to chloride-containing environments.

Durability of self-healing ultra-high-strength reinforced micro-concrete under freeze–thaw or chloride attack

The durability of an innovative self-healing micro-concrete in aggressive environments simulated by freeze–thaw cycles and salt spray test is studied. Tests are conducted on an ultra-high-strength reinforced micro-concrete that incorporates an autonomous self-healing mechanism based on the reaction of an epoxy compound enclosed within silica microcapsules and amine functionalised silica nanoparticles distributed within the cementitious matrix. The effect of aggressive environments is analysed in the self-healing micro-concrete and in a reference micro-concrete stored for 28 d in laboratory conditions after cracking, for crack widths of 150 and 300 μm. The results of capillary water absorption tests, complemented by electron microscopy analysis, confirm the enhanced durability of the autonomously self-healed material in both the freeze–thaw and the salt spray tests, as compared to the reference micro-concrete. In conclusion, the innovative self-healing mechanism is expected to increase the service life of structures in humid, cold climates and chloride-containing environments.

High corrosion and wear resistance of Al-based amorphous metallic coating synthesized by HVAF spraying

A uniform and dense Al-based amorphous metallic coating was deposited on AA 2024 substrate by high velocity air fuel (HVAF) spraying. The Al86Ni6Y4.5Co2La1.5 alloy with high glass forming ability was adopted to prepare the feedstock powder. The coating exhibited 0.12% porosity and 83.7% volume fraction of amorphous phase. The corrosion and wear resistance of the coating were investigated compared to AA 2024. It was found that the coating presented an enhanced pitting potential and a lower corrosion potential than that of AA 2024, providing a sacrificial anode-based cathodic protection for the substrate under chloride-containing environment. The excellent corrosion resistance stems from the smaller driving force for the adsorption of aggressive anions and lower carrier density in passive film formed on amorphous coating. The wear resistance of Al-based amorphous coating was apparently superior to AA 2024 substrate, which is primarily associated with the formation of an even and protective oxide film.

The interaction of corrosion fatigue and stress-corrosion cracking in a precipitation-hardened martensitic stainless steel

Fracture mechanics-based testing was used to quantify the stress-corrosion cracking and corrosion fatigue behavior of a precipitation-hardened martensitic stainless steel (Custom 465-H950) in full immersion chloride-containing environments at two applied electrochemical potentials. A plateau in the cycle-based crack-growth kinetics (da/dN) was observed during fatigue loading at low ΔK and [Cl−] at and above 0.6 M. Evaluation of the fracture morphology and frequency dependence of this plateau behavior revealed an intergranular fracture surface morphology and constant time-dependent growth rates. These data strongly support a controlling stress-corrosion cracking mechanism occurring well below the established KISCC for quasi-static loading. Low-amplitude cyclic loading below ΔKTH (i.e., “ripple loads”) is hypothesized to enable time-dependent intergranular-stress-corrosion cracking to occur below the KISCC via mechanical rupturing of the crack-tip film and enhancement of the H embrittlement-based SCC mechanism.

Pitting Initiation and Propagation of X70 Pipeline Steel Exposed to Chloride-Containing Environments.

Inclusion-induced pitting initiation mechanisms in X70 steel were investigated by scanning electron microscopy, scanning Kelvin probe force microscopy (SKPFM), immersion and electrochemical polarization tests in chloride-containing ion solutions. There are three inclusion types in the X70 steel. Corrosion test results indicated that pitting corrosion resistance of type A inclusion < type C inclusion < type B inclusion, i.e., (Mn, Ca)S < matrix < (Al, Ca)O. SKPFM test results show that the type A inclusion exhibited both lower and higher potentials than the matrix, while the type B inclusion exhibited higher potential than the matrix. The corrosion test and the SKPFM potential test results are consistent. Potentiodynamic polarization results indicate that the type A and C are active inclusions, while the type B is an inactive inclusion. Three kinds of possible mechanisms of inclusion-induced pitting corrosion are established for the X70 steel.

A novel dioxime compound for protecting copper in neutral chloride solutions and to treat bronze disease in archaeological artefacts

This study aimed to evaluate (4,6-dihydroxy benzene-1,3-dicarbaldehyde dioxime (DBDD)) as a novel corrosion inhibitor for protecting copper in neutral sodium chloride (NaCl) solutions and conserving archaeological copper-based artefacts suffering from bronze disease. Potentiodynamic polarisation techniques showed that DBDD was effective in inhibiting copper corrosion in 3.5 wt. % NaCl solution. An Iron Age copper-based fibula was used for testing DBDD; X-ray diffraction (XRD) analysis showed that it was suffering from bronze disease before treatment was initiated. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and Fourier transform infrared (FTIR) spectroscopy investigations showed that DBDD coordinated with copper ions in the corrosion products and formed a protective film on the surface. Investigating the interaction of DBDD with pure copper chloride and carbonate minerals representing corrosion products appearing on archaeological artefacts proved the formation of new passive species between DBDD and these minerals. The fibula treated with DBDD showed no signs of corrosion after exposure to high relative humidity. It was concluded that DBDD was effective in protecting copper exposed to a neutral chloride-containing environment and passivating corrosion products appearing on heavily corroded archaeological artefacts suffering from bronze disease.

Localized Corrosion Characteristics of Nickel Alloys: A Review

There are a great variety of commercial nickel alloys mainly because nickel is able to dissolve a large amount of alloying elements while maintaining a single ductile austenitic phase. Nickel alloys are generally designed for and used in highly aggressive environments, for example, those where stainless steels may experience pitting corrosion or environmentally assisted cracking. While nickel alloys are generally resistant to pitting corrosion in chloride-containing environments, they may be prone to crevice corrosion attack. Addition of chromium, molybdenum and tungsten increases the localized corrosion resistance of nickel alloys. This review on the resistance to localized corrosion of nickel alloys includes specific environments such as those present in oil and gas upstream operations, in the chemical process industry and in seawater service.

Study on the Initial Atmospheric Corrosion Behavior of Copper in Chloride-Containing Environments

Study on the Initial Atmospheric Corrosion Behavior of Copper in Chloride-Containing Environments

Surface treatment and corrosion behaviour of austenitic stainless steel biomaterial

In this article results from corrosion behaviour of austenitic stainless steel AISI 316L after different surface treatments are published. “As received” surface and surface after grinding resulted in lower resistance to pitting corrosion in physiological solution than electrochemically polished in H3PO4+H2SO4+H2O. Electropolishing also improved the surface roughness in comparison with the “as received” surface. Deposition of Al2O3 nanometric ALD coating improves the corrosion resistance of stainless steel in chloride-containing environment by shifting the breakdown potential toward more positive values. This oxide coating not only improves the corrosion resistance but it also affects the wettability of the surface, resulting in hydrophobic surface.

Hydrophobicity and Improved Localized Corrosion Resistance of Grain Boundary Etched Stainless Steel in Chloride-Containing Environment

Localized corrosion of stainless steels by chloride ions in seawater leads to metal degradation while fouling of marine organisms increases the occurrence of localized corrosion. We describe a simple method to increase hydrophobicity of austenitic stainless steel using grain boundary etching that can also inhibit adhesion of bio-organisms present in seawater as well as increase the localized corrosion resistance of stainless steel in chloride-containing aqueous environments. This paper describes the corrosion behavior of stainless steel as a result of grain boundary etching to achieve hydrophobicity. Potentiostatic polarization on stainless steel 316L in a nitric acid solution at an anodic potential of 1.3 V vs. saturated calomel electrode (SCE) results in a grain boundary etched structure and a Cr- and Mo-rich passive film as confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. This modified stainless steel 316L surface exhibits enhanced corrosion resistance to a 0.6 M sodium chloride solution. Specifically, potentiodynamic polarization studies indicate that the breakdown potential increases and the sample-to-sample variability decreases. The modified surfaces show a narrow range of breakdown potentials (0.96 to 1.05 V vs. SCE) compared to as-received stainless steel 316L (0.32 to 0.86 V vs. SCE).

SIMULATION OF CORROSION WITH THE INFLUENCE OF THE STRESS-STRAIN STATE, TEMPERATURE AND CONCENTRATION OF AGGRESSIVE ENVIRONMENT ON THE CORROSION RATE

Ponte Academic JournalMar 2017, Volume 73, Issue 3 SIMULATION OF CORROSION WITH THE INFLUENCE OF THE STRESS-STRAIN STATE, TEMPERATURE AND CONCENTRATION OF AGGRESSIVE ENVIRONMENT ON THE CORROSION RATEAuthor(s): I. I. Ovchinnikov ,I. G. Ovchinnikov, O.V. SnezhkinaJ. Ponte - Mar 2017 - Volume 73 - Issue 3 doi: 10.21506/j.ponte.2017.3.27 Abstract:We consider the modeling and prediction of corrosion of metal wear in aggressive environments. A model of corrosive wear in the form of a differential equation, which takes into account the impact of the state of stress, temperature and concentration of chloride-containing environments. On the basis of experimental data the specified ratios and conducted model identification. Download full text:Check if you have access through your login credentials or your institution Username Password

Influence of Ferrite Phase Content on the Electrochemical Properties of Duplex Stainless Steels

Duplex stainless steels have a large number of industrial applications and may replace high cost materials, especially in chloride-containing environments like seawater in off-shore platforms due to their high mechanical properties and good corrosion resistance. The influence of the ferrite content on the performance of duplex stainless steels in these corrosive environments is not well known. For the present paper, new superduplex stainless steels with ferrite between 30 and 60% were developed and their microstructure and corrosion resistance were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in NaCl 3.5% (wt %) at 26°C and 78°C. The results obtained at 26°C showed that the pitting potential (Epitt) is little affected by the ferrite content, but for the materials with higher ferrite it was possible to observe an increase in the repassivation potential with a decrease in the corrosion potential and passive currents due to the presence of more resistive passive films. Tests performed at 78°C indicated a high decrease in the Epitt for all the samples, independently of the ferrite percentage, although maintaining superiority in higher ferrite content. Alloys with a 55% ferrite phase content, i.e. less dependent of Ni element, present a superior performance of corrosion resistance.

Effect of Cr Content on Pit Initiation Behavior at MnS Inclusions in Fe-Cr Steels

It is well known that Cr improves the pitting corrosion resistance of stainless steels. In chloride-containing environments, MnS inclusions act as a preferential site for pit initiation of stainless steels. In this study, a microelectrochemical approach was applied to elucidating the effect of Cr addition on the corrosion resistance of pit initiation at MnS inclusions. Fe-5Cr, Fe-12Cr, and Fe-18Cr steels, containing 0.027 mass% S, were prepared by vacuum induction melting. Heat treatment was performed at 1123 K for 600 s. After the heat treatment, the steels were water-quenched. Their surfaces were polished down to 1 μm diamond paste. Since the MnS inclusions are darker than the steel matrix, they are clearly visible in the as-polished condition without etching, and it was confirmed that the inclusions consisted of Mn, S, and a small amount of Cr. This type of inclusion was simply referred to as MnS inclusion. In order to ascertain the dissolution potential of the MnS inclusion, the potentiodynamic polarization curves for the small areas with the inclusion were taken in a naturally aerated 0.1 M Na2SO4 solution at 298 K. As shown in Fig.1a, the increase in current density around 0.05 V was a characteristic common to all the specimens. After the polarization, the inclusions were observed by a field emission scanning electron microscope equipped with an X-ray energy-dispersive spectrometer, and it was concluded that the current increase around 0.05 V was due to the dissolution of the MnS inclusion. Figure 1b shows the potentiodynamic polarization curves for the small areas with the inclusion in a naturally aerated 0.1 M NaCl solution at 298 K. In the cases of Fe-5Cr and Fe-12Cr, the large current increases were observed around 0.05 V. It was suggested that the MnS dissolution directly brings about the initiation of pit (Fig1c-e). On the other hand, no stable pit was initiated on Fe-18Cr. Moreover, even the initiation potential of meta-stable pit was higher than the inclusion dissolution potential. The addition of Cr in the steels was shown to improve the repassivation ability of the steel matrix. Figure 1

SECM Study of Effect of Chromium Content on the Localized Corrosion Behavior of Low-Alloy Steels in Chloride Environment

This paper investigates the effect of chromium (Cr) content (0, 1, 3 and 5% Cr) in epoxy-coated alloy steel against corrosion using in situ electrochemical techniques such as EIS and SECM in a 3% NaCl solution. The EIS results revealed that the epoxy-coated Cr steel exhibited higher impedance values than carbon steel, which is attributed to the greater resistance of Cr steel toward corrosion. Based on the cyclic voltammogram results, the tip potentials were set at −0.7, 0.04 and 0.60 V for determining the concentration of dissolved oxygen at cathodic region, and oxidation of Cr2+ and Fe2+ at anodic region, respectively. The SECM measurements showed that, the tip current in the anodic region has decreased with increase in Cr content of the sample, which indicates that the oxidation of Fe2+ and Cr2+ decreases (corrosion is reduced) with the increase in Cr content of the steel. Besides, 5% Cr steel can maintain the highest corrosion resistance, and 1 and 3% Cr steels have higher corrosion resistance than the 0% Cr steel. This higher corrosion resistance of Cr steel samples could be due to the formation of Cr-rich hydro-oxide layers [Cr(OH)3 as a corrosion product] on the surface of the samples. Thus, the epoxy-coated Cr alloy steel has greater corrosion resistance in a chloride-containing environment than the carbon steel. Hence, epoxy-coated Cr alloy steel can be successfully used as a construction material in structures.