Local Corrosion Rate Research Articles

(Invited) Understanding the Role of Al3+ in Accelerated Testing and Its Impact on the Protective Oxide Film of AA2060

In accelerated corrosion testing of aluminum-alloys, the stability of the protective oxide layer has a significant impact on corrosion rate and morphology. Many times the oxide layer is intentionally weakened during accelerated tests. An acidic solution pH can increase the general corrosion rate by uniformly thinning the oxide film, and a high chloride concentration can increase localized corrosion rates. Recent work has suggested that other chemical species may also impact the oxide film of aluminum during accelerated testing. In this study, aluminum-lithium alloy 2060 was tested in solutions of 1 M sodium chloride (NaCl) and 0.1 M potassium sulfate (K2S2O8) with and without the addition of a small amount (0.022 M) of aluminum chloride (AlCl3). The K2S2O8 was an oxidizing agent added to provide a fast cathodic reaction during corrosion. It was found that even a small amount of Al3+ could dramatically increase the frequency of attack for AA2060 as shown in Figure 1. Linear polarization was used to compare electrochemical kinetics with and without added Al3+, and samples that were tested with 0.022 M AlCl3 had a significantly higher diffusion limiting current (ilim) and consequently, a higher corrosion rate. For the near peak-aged AA2060-T86 temper, ilim was twenty-eight times higher with 0.022 M AlCl3 than without. The impact on the under-aged AA2060-T36 temper was smaller, but still significant at over three times higher ilim with added Al3+. The concentration of oxidizing agent was the same in tests with and without added Al3+, so these results suggest that the increase in i­lim may be due to increased diffusion through the protective oxide film. To further investigate this phenomenon, electrochemical impedance measurements will be used to study the oxide film of AA2060 in solution with and without added Al3+. Figure 1

Structure and in vitro bioactivity of ceramic coatings on magnesium alloys by microarc oxidation

Magnesium and its alloys have the potential to serve as lightweight, degradable, biocompatible and bioactive orthopedic implants for load-bearing applications. However, severe local corrosion attack and high corrosion rate have prevented their further clinical use. Micro-arc oxidation (MAO) is proved to be a simple, controllable and efficient electrochemistry technique that can prepare protective ceramic coatings on magnesium alloys. In this paper, electrolyte containing silicate salts was used for microarc oxidation to form ceramic bioactive coatings on the ZK61 alloy substrate. The structure characteristics and element distributions of the coating were investigated by XRD, TEM, SEM and EPMA. The MAO samples were immersed in simulated body fluid (SBF) for 7 and 14days, respectively. The surface characteristic of the immersed coatings was investigated by Fourier-transform infrared (FTIR) spectroscopy. The results show that these MAO coatings have low crystallinity and are mainly composed of MgO, Mg2SiO4 and Mg2Si2O6. The coating surface is porous. During the SBF immersion period, the nucleation and precipitation of bone-like apatites occur on the MAO coating surface. The corrosion resistance of the substrate is improved by the MAO coatings.

Measurement of localized corrosion rates at inclusion particles in AA7075 by in situ three dimensional (3D) X-ray synchrotron tomography

In situ X-ray synchrotron tomography was used to measure the localized corrosion rate of Mg2Si particles present in 7075 aluminum alloys in deionized ultra-filtered (DIUF) water. The evolution of hydrogen bubbles was captured as a function of time and the measured volume was used to calculate the local corrosion rate of Mg2Si particles. It was shown that in the absence of chloride ions, stress was needed to create fresh particle surfaces, either by fracture or debonding, to initiate corrosion at the particles.

Multidimensional Modeling of Nickel Alloy Corrosion inside High Temperature Molten Salt Systems

One challenge with concentrated solar power (CSP) systems is the potential corrosion of the alloys in the receivers and heat exchangers at high-temperature (700–1000°C), which leads to a reduction of heat transfer efficiency and influences the systems durability. In this work, a corrosion model has been developed to predict the rates and mechanisms for corrosion of a nickel-based alloy that is in contact with a molten salt heat transfer system. In addition to accounting for heat and mass transfer effects on the corrosion, the model takes into account the electrochemical kinetics. Coupled with computational fluid dynamics (CFD), the local electrochemical environment and corrosion rates in a high-temperature molten salt system can be predicted. The kinetic, heat and mass transfer parameters used in the model are based on experimental studies conducted in a thermosiphon. The immersion cell was designed to expose coupons to the molten salt at isothermal or non-isothermal conditions between 700–1000°C. The model can predict the effect of thermal gradients between the top and the bottom of the reactor which induce natural convection of the molten salt. The model has been validated against experimental results at different isothermal and non-isothermal conditions and good agreement has been achieved between the model predictions of the corrosion rates and corrosion potentials with the experimental observations.

Long-term corrosion of austenitic steels in flowing LBE at 400 °C and 10−7 mass% dissolved oxygen in comparison with 450 and 550 °C

Long-term corrosion tests for up to ∼13,194 h on 1.4970 (15-15 Ti), 316L and 1.4571 austenitic steels were carried out at 400 °C in flowing LBE (2 m/s) with 10−7 mass% dissolved oxygen. The steels show general slight oxidation (Cr-based oxide film) along with local, pit-type solution-based corrosion attack. The incubation time for pit-type attack is ∼4500 h. After ∼13,194 h, the maximum pit depth observed was ∼14, 23 and 57 μm for 1.4970, 316L and 1.4571, respectively, that corresponds to local corrosion rates of ∼6, 10 and 26 μm/year. At 450 °C and 550 °C, the corrosion rates are ranged in between ∼120−220 μm/year and ∼500–3000 μm/year, respectively. Corrosion appearances and mechanisms are discussed.

Defects in epoxy‐coated reinforcement and their impact on the service life of a concrete structure

AbstractEpoxy‐coated reinforcement (ECR) as a means of protection against chloride‐induced corrosion of steel in concrete is used in only a few countries due to doubts concerning its effectiveness. A common misconception is that possible defects in the coating are particularly weak points as these might favour high local corrosion rates and thus loss of steel cross‐section. This work discusses why a certain number of small defects can be tolerated. It is argued that prolongation of the initiation phase is caused by a higher critical chloride content compared with uncoated steel due to the “size effect”. Additionally, the propagation phase for ECR is likely to be extended due to the severely restricted cathodic area that limits the corrosion rate. This paper presents experimental and numerical tests to verify these assumptions.

Multidimensional Modeling of Nickel Alloy Corrosion inside High Temperature Molten Salt Systems

Concentrated solar power (CSP) systems in the presence of high operating temperature heat transfer fluids for power production processes has attracted more attention in recent years. The challenge with these systems is the corrosion of alloys at high-temperature (700-1000°C) in receivers and heat exchangers causing a reduction in heat transfer efficiency and influencing the apparent durability [1-3]. In this work, a corrosion model that includes thermal gradients and fluid flow is developed to predict corrosion rates and mechanisms observed in a nickel base alloy in contact with a molten salt heat transfer system. The model takes into account the electrochemical kinetics in addition to mass transfer-limited corrosion coupled with a computational fluid dynamic (CFD) model that can predict the local electrochemical environment and corrosion rates in a system with temperature and fluid flows. The kinetic and mass transfer parameters used in the model are based on the experimental coupon studies were conducted between 700-1000 °C within molten salt in a thermosiphon reactor that designed to allow exposure the coupons to the non-isothermal condition. The thermal gradients between top and bottom of the reactor could induce natural convection of the salts [4-5]. Fig. 1 shows an example of the model prediction of corrosion rate distribution, i (A/cm2) at coupon surfaces at both hot and cold zones in addition to the temperature gradient near the wall and streamlines that show the flow pattern of molten salt inside the thermosiphon. the This corrosion model accounts for the effects of different operational conditions such as temperature and component concentrations in addition to the alloy surface properties on the corrosion rate. Acknowledgements The authors gratefully acknowledge the financial support for this work from the DOE EERE SunShot Initiative (DE-AC36-08GO28308) under a subcontract from SRNL to the University of Alabama and to the University of South Carolina. The authors also thank the University of South Carolina Center for Fuel Cells and the CD-adapco group for their support. R eferences C. Forsberg, P.F. Peterson, and H.H. Zhao, J. Sol. Energy Eng. Trans.-ASME, 129, 141-146, 2007.C. Forsberg, Progress in Nuclear Energy, 47, 32-43, 2005.D. Ludwig, L. Olson, K. Sridahran, M. Anderson, and T. Allen, Corrosion Engineering Science and Technology, 46, 360-364, 2011.B. L. Garcia-Diaz, L. Olson, M. Martinez-Rodriguez, R. Fuentens, J. Gray. paper #741, 2014 ECS and SMEQ Joint International Meeting, Cancun, Mexico, Oct. 08, 2014.R. Fuentens, L. Olson, M. Martinez-Rodriguez, J. Gray, B. L. Garcia-Diaz. paper #743, 2014 ECS and SMEQ Joint International Meeting, Cancun, Mexico, Oct. 08, 2014. Figure 1. Corrosion rate distribution, i (A/cm2) at coupon surfaces at both hot and cold zones in addition to the temperature gradient near the wall and streamlines inside the thermosiphon. Figure 1

20 Years of Corrosion Sensing and Microvisualization of Corrosion Processes

Localized corrosion processes continue to be a major cause for degradation failure in damaging fluids. Initiation stages of response remain difficult to characterize, arising in part because of the difficulty in being able to predict the location and onset of the attack. Propagation stages are seldom constant but change with time due to competing processes of dissolution and product deposition at the corrosion sites. The progress of the attack changes the local environmental concentrations which are especially important at buried interfaces that are isolated from bulk conditions. The present paper will describe some of the recent advances in optical, electrochemical, and microscopy that are directed at providing local information on “precursor sites” and vulnerable areas on metal and covering oxide surfaces. Previous studies of coupled reactions on reactive surfaces provide a general basis for the work to be described here. The objectives of the experimental techniques are: (1) to measure the local corrosion rate; (2) to locate breakdown sites, and; (3) to study the fundamental properties of passive films and how they are related to the stability of the films and damaging environments. The latter is of particular interest since it will allow one to predict why a particular precursor site is more vulnerable to breakdown as compared to neighboring areas. In locating precursor sites, entire regions of the corroding surface can be imaged concurrently or point-by-point using scanned probe or beam. Both classes will be discussed with their capabilities. The techniques used in our laboratory are: (1) the Quartz Crystal Microbalance (QCM); (2) Optical Fiber Micromirrors (FOP); (3) Confocal Laser Scanning Microscopy (CLSM); (4) Photoelectrochemical Microscopy (PEM); (5) Scanning Electrochemical Microscopy (SECM); (6) Scanning Photoelectrochemical and Electrochemical Microscopy (SPECM); (7) Near Field Scanning Optical and Spectroscopic Microscopy (NSOSM). The experimental setup for each and the capability help to reveal the advantages that are offered by them. Optical sensing by the QCM and optical fiber micromirrors have been used to measure corrosion rates, with sensitivity of fractions of an atomic layer. Similar to them but with the capability to image a larger reactive surface is the CLSM to determine local attack rates at various surface sites. The NSOSM is valuable to obtain both vertical and lateral super resolution images of reacting surfaces of about 60 nanometers. The techniques support the development of miniature corrosion sensors devoted to monitoring reactive surfaces in remote and occluded regions, coupled with wireless transmission.

The influence of SO2 on the tolerable water content to avoid pipeline corrosion during the transportation of supercritical CO2

A systematic study is undertaken to establish the influence of sulfur dioxide (SO2) concentration on the critical water content required to avoid substantial levels of internal corrosion during the transport of supercritical CO2 for carbon capture and storage (CCS) applications. Corrosion experiments were performed on X65 carbon steel in autoclaves containing supercritical CO2 at 80bar and 35°C in the presence of 0, 50, and 100ppm (mole) SO2. General and localized corrosion rates were determined over a period of 48h through the implementation of gravimetric analysis and surface profilometry, respectively. Analysis of corrosions products formed on the steel surface was performed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results indicate that the presence of SO2 reduces the critical water content required to maintain a general corrosion rate below 0.1mm/year. Furthermore, the water content required to avoid excessive localized corrosion is far less than that to prevent significant general corrosion. Localized corrosion rates close to 1mm/year were observed in the absence of SO2 when the CO2 system was water-saturated, but below water contents of ∼1800ppm (mole) and ∼500ppm, general and localized corrosion rates (respectfully) were found to be below 0.1mm/year even in the presence of 100ppm SO2. The research presented highlights that reducing water content is a more favorable option compared to reducing SO2 content to minimize internal pipeline corrosion during transportation. Consideration is also afforded to the consumption of impurities in the closed system experiments.

Determination of the local corrosion rate of magnesium alloys using a shear force mounted scanning microcapillary method.

The successful development of scanning probe techniques to characterize corrosion in situ using multifunctional probes is intrinsically tied to surface topography signal decoupling from the measured electrochemical fluxes. One viable strategy is the shear force controlled scanning microcapillary method. Using this method, pulled quartz micropipettes with an aperture of 500 nm diameter were used to resolve small and large variations in topography in order to quantify the local corrosion rate of microgalvanically and galvanically corroded Mg alloys. To achieve topography monitoring of corroded surfaces, shear force feedback was employed to position the micropipette at a reproducible working height above the substrate. We present proof of concept measurements over a galvanic couple of a magnesium alloy (AE44) and mild steel along with a microgalvanically corroded ZEK100 Mg alloy, which illustrates the ability of shear force to track small (1.4 μm) and large (700 μm) topographic variations from high aspect ratio features. Furthermore, we demonstrate the robustness of the technique by acquiring topographic data for 4 mm along the magnesium-steel galvanic couple sample and a 250 × 30 μm topography map over the ZEK100 Mg alloy. All topography results were benchmarked using standard optical microscopies (profilometry and confocal laser scanning microscopy).

Optical measurement of uniform and localized corrosion of C1018, SS 410, and Inconel 825 alloys using white light interferometry

We describe the use of a vertical scanning interferometer (VSI) to quantitatively measure the uniform and localized corrosion rates of different metal alloys used in the oil and gas industry. Based on white light interferometry, the most significant advantage is the large field of view in combination with nanometer Z-resolution for fast and accurate surface measurements. Corrosion rates were calculated directly from VSI data and verified by weight loss analysis. We explored the quantitative impact of high temperature and high salinity on C1018, SS 410 and I-825 alloys. VSI data for uniform corrosion correlated well with data from weight loss analysis.

Filtration–UV irradiation as an option for mitigating the risk of microbiologically influenced corrosion of subsea construction alloys in seawater

The effect of filtration–UV irradiation of seawater on the biofilm activity on several offshore structural alloys was evaluated in a continuous flow system over 90days. Biofilms ennobled the electrode potential by +400 to 500mV within a few days of exposure to raw untreated seawater. Filtration–UV irradiation of the seawater delayed the ennoblement of the steels for up to 40days and lowered localized corrosion rates in susceptible alloys. Ennobling biofilms were composed of microbial cells, diatoms and extracellular polymeric substances and the bacterial community in biofilms was affected by both the alloy composition and seawater treatment.

Influence of Edge Effects on Local Corrosion Rate of Magnesium Alloy/Mild Steel Galvanic Couple

The effect of the insulator-mixed-material edge on the galvanic corrosion rate of magnesium alloy (AE44)-mild steel (MS) couple is experimentally studied using scanning vibrating electrode technique (SVET), profilometry, and classical electrochemistry. The local and average corrosion rates estimated from the experimental depth of anodic attack profile of AE44-MS couple are validated by 2D and 3D corrosion numerical models. Our study demonstrates experimentally and theoretically that the presence of the insulator edge increases the local current density, which enhances the corrosion rate. The extent of the local corrosion rate enhancement and its effect on the overall corrosion rate of the mixed material is discussed and depends on the mixed material's geometry and the edge type.

Localized Corrosion of Binary Mg-Nd Alloys in Chloride-Containing Electrolyte Using a Scanning Vibrating Electrode Technique

The influence of neodymium (Nd) alloying additions in the 0.47 wt% to 3.53 wt% range on the localized corrosion behavior of Mg, when freely corroding in aqueous sodium chloride (NaCl) electrolyte, is investigated using an in situ scanning vibrating electrode technique (SVET). For all samples, the point of surface breakdown is an intense focal anode that expands radially with respect to time, revealing a cathodically activated interior, which is galvanically coupled with the local anode at the perimeter. However, for Nd compositions of ≤0.74%, radial expansion ceases within ca. 2 h of initiation, whereupon dark filiform-like corrosion features are observed, which traverse over the exposed Mg surface. For Nd additions of ≥1.25%, the radial expansion continues with time up to a point where the entire intact surface becomes consumed. The intensity of the local anode ring of circular corroded regions is seen to increase as more cathodically activated corroded surface becomes exposed. Mean current density values measured within these corroded areas increase progressively with Nd content, leading to a progressive rise in localized corrosion rates. The cathodic activation of corroded regions is proposed to derive from an enrichment of noble, Nd-rich intermetallic grains caused as the alpha-Mg phase becomes attacked at local anode sites.

On the problem of theoretical estimation of alloying additives effect on susceptibility of zirconium alloys to nodular corrosion

Several mechanisms of nodular corrosion are discussed in literature for Zr-based alloys. One of the mechanisms is attributed to instability of the uniform corrosion front with respect to transverse perturbations. According to this mechanism, a nonuniform field of mechanical stress is formed at the disturbed metal–oxide interface. It leads to redistribution of alloying elements in the vicinity of the corrosion front and concentration of additives in the metal becomes inhomogeneous. Depending on properties of the particular additive and its effect on local corrosion rate, the drift in the field of mechanical stress may lead to either enhancement or suppression of the arising perturbations. In the present paper, this approach for nodular corrosion understanding is further developed. An analytical solution for mechanical stresses in the metal–oxide system with undulated interface is reported. For undulations of small amplitude the solution is built in the frame of elastic theory. Results of analysis are applied to additives of Fe, Cr, Ni and Sn in Zircaloy-type alloys. Effects of both solutes and precipitates of these additives on susceptibility of alloys to nodular corrosion are considered.

A Review of Recent Patents on Coupled Multielectrode Array Sensors for Localized Corrosion Monitoring

The coupled multielectrode array sensor (CMAS) is an emerging technology for monitoring localized corrosion, such as pitting, intergranular attack, crevice corrosion, or other forms of nonuniform corrosion. The technique has been used for online, real-time corrosion monitoring in laboratories and field systems. In this paper, the patents related to the development of CMAS technology for localized corrosion monitoring are reviewed. These patents include applications in mapping or monitoring localized corrosion; methods for localized corrosion rate measurements; method to minimize internal current; improvement in electronics and software; planar CMAS probe; and high-temperature electrochemical sensors. Current and future developments of this corrosion monitoring technology are discussed. Keywords: Coupled Multielectrode Array Sensors, Corrosion monitoring, Localized corrosion, electrochemical sensor, multielectrode array, high-temperature electrochemical sensor, pitting, anodic electrodes, Multielectrode systems, electrode arrays, wire-beam electrode, Multi-phase corrosion, multielectrode sensors, carbon-coated electrodes, stainless steel

INVESTIGATION OF THERMO-PHYSICAL AND FLOW PROPERTIES OF CO2 HYDRATE SLURRY

A pilot CO2 hydrate slurry production system was built and tested. The density of CO2 hydrate slurry was experimentally investigated and the relation between the density and the solid fraction has been established. The apparent viscosity of water, CO2 solution and CO2 hydrate slurry was investigated with a XL7-100 online resonant viscometer. We find that when the solid mass fraction in slurry increases, the density and apparent viscosity of CO2 slurry also increase. CO2 hydrate solid particles contribute only slightly to the viscosity increase when the solid mass fraction increased from 1.59% to 28% from our experimental results. Higher solid mass fraction can be achieved when more CO2 gas is injected into the loop under suitable hydrate formation conditions. The pure hydrate's dissociation enthalpy was evaluated by Micro Differential Scanning Calorimetry system. The enthalpy of CO2 hydrate slurry mainly depends on solid mass fraction. Real-time coupled multielectrode array sensor probes were applied to measure the maximal localized corrosion rate of three different materials subjected to CO2 hydrate slurry and saturated CO2 solution in the temperature range of 274.15–291.15 K and pressure range of 2.5–3.0 MPa. For a long-term usage in a mixture of CO2 saturated aqueous solution and hydrate slurry environment, carbon steel materials are to be unacceptable from the corrosion resistance point of view. In contrast, stainless steel type 304L and copper 110 have presented very low corrosion rates.

Localized CO2 corrosion propagation at moderate FeCO3 supersaturation initiated by mechanical removal of corrosion scale

The propagation of localized CO2 corrosion was investigated at moderate iron carbonate supersaturation using an artificial defect method with re-formed corrosion scale. A mechanical tool was developed which locally removed pre-formed iron carbonate scale and initiated localized corrosion at a FeCO3 supersaturation of 3–10. The localized corrosion rate was calculated based on electrochemical measurement using a simplified algorithm and was also measured at the deepest part of the defect using scanning electron microscopy. Localized corrosion was driven by a galvanic cell established between the two surfaces exposed in the artificial defect where an open circuit potential difference was maintained.

Localized Corrosion of 304 Stainless Steel under a NaCl Droplet

The distributions of corrosion potential and galvanic current of 304 stainless steel under a NaCl droplet were studied by using the wire beam electrode (WBE). It was found that the distributions of the electrochemical parameters were heterogeneous with isolated anodic and cathodic zones appeared randomly. During the corrosion process, the polarity of some anodes changed with the evolution of time. The localized corrosion rate and heterogeneity increased firstly, and then decreased afterward with the increase of time, which can be attributed to the cooperative effects of the aggressive ions and the corrosion products.

Internal Current Effects on Localized Corrosion Rate Measurements Using Coupled Multielectrode Array Sensors

Abstract Coupled multielectrode array sensors (CMAS) have been used for real-time monitoring of corrosion, particularly localized corrosion. The internal anodic current on the most anodic electrode...