Linear Polarization Resistance Tests Research Articles

A comprehensive study on hot corrosion resistance of NiCoCrAlYTa and NiCrAl thermal-sprayed coatings for CSP applications

The new generation of concentrated solar power (CSP) plants could be able to work at temperatures up 650 °C and carbonates molten salts are one of the main candidates to be used as thermal energy storage (TES) materials. Molten salt corrosion has been defined as one of the main issues and the technology demands more resistance alloys and innovative coatings. In this study, the assessment of hot corrosion resistance for NiCoCrAlYTa and NiCrAl thermal-sprayed coatings has been undertaken, tested on a ternary eutectic mixture (Li2CO3-Na2CO3-K2CO3) at a temperature of 650 °C. Electrochemical impedance spectroscopy and linear polarization resistance tests were used to evaluate the behaviour of the coatings but the obtained results reveal high values of corrosion rates accompanied by the formation of cracks. This unsatisfactory performance of the coatings, analysed by scanning electron microscopy and x-ray diffraction, can be attributed to a combination of different factors such as porosity, internal material stresses and thermal diffusion phenomena. As a result, it is concluded that further research is necessary to explore new coating application techniques.

The adsorption and inhibition efficiency of 2-amino-4-methoxy-6-methyl-1,3,5-triazine for corrosion of mild steel in hydrochloric acid solution

PurposeThis study aims to prevent mild steel (MS) against corrosion in 0.5 M HCl solution, 2-amino-4-methoxy-6-methyl-1,3,5-triazine was used. The effectiveness of the compound as a corrosion inhibitor was studied via electrochemical, surface and theoretical calculation techniques.Design/methodology/approachFor concentrations ranging from 0.5 to 10.0 mM, almost similar polarization resistances were obtained from electrochemical impedance spectroscopy (EIS) and linear polarization resistance tests. It also investigated inhibitive activity of 2-amino-4-methoxy-6-methyl-1,3,5-triazine on the steel surface using scanning electron and atomic force microscope instruments. Langmuir adsorption is the best matched isotherm for the adsorption of the inhibitor to the steel surface.FindingsEIS method was used to determine inhibition efficiency, which was determined to be 95.7% for 10.0 mM inhibitor containing acid solution. Density functional theory’s predictions for quantum chemistry agreed well with the other experimental results.Originality/valueThe methods used in this study are effective and applicable; the used organic inhibitor is 2-amino-4-methoxy-6-methyl-1,3,5-triazine; and protective effectiveness is important, which is crucial for the task of MS corrosion prevention.

(Digital Presentation) Investigation of Microstructure Dependent Inhibitor Adsorption Mechanism on Carbon Steel By in Situ Atomic Force Microscopy

In the petroleum industry, organic surfactant type inhibitors have been widely applied in the oil and gas industry considering their high efficiency. Carbon steels with various carbide contents have also been used extensively as pipeline materials during the transport and storage of crude oil due to their excellent mechanical properties and low cost. The previous investigation of inhibition mechanism on carbon steel is limited by lack of surface characterization techniques at a molecular level. Atomic force microscopy (AFM) can not only provide localized visual observation, but can also achieve the detection of mechanical properties of an inhibitor film. In this study, in situ AFM contact mode friction imaging and in situ AFM tapping mode phase imaging techniques have been applied to investigate the influence of the ferritic-pearlitic microstructure of carbon steel on inhibitor adsorption mechanisms during CO2 corrosion under different inhibitor concentrations. At concentration above surface saturation, AFM contact mode friction images show a large friction contrast between inhibitor covered cementite structures and ferrite structures, while in the absence of inhibitor, this friction contrast almost disappears, indicating the inhibitor adsorption induced this difference. AFM tapping mode phase images indicate uniform adsorption of inhibitor on both cementite and ferrite structures.The differences observed in these AFM analyses indicate that the adhesion force of inhibitor molecules on cementite could be smaller than on ferrite, or the molecular orientations of inhibitor molecules adsorbed on cementite and ferrite structures could be different. The special adsorption behavior of inhibitor molecules on cementite means the carbide component of the microstructure could directly influence inhibitor adsorption and may decrease inhibitor efficiency. Simultaneous linear polarization resistance tests in electrochemical AFM (EC-AFM) cell indicates a maximum inhibition efficiency at concentration above saturation.Keywords : Contact mode AFM, friction contrast, tapping mode AFM, phase contrast, cementite, ferrite, organic inhibitor, adhesion force.Statement of importance:Studies related to inhibitor adsorption mechanisms on ferritc-pearlitic carbon steels can be connected with the practical issues that iron carbide can impair the corrosion inhibitor performance on carbon steels. This AFM work connects the corrosion inhibition effect with the carbon steel components at a molecular level for the first time. Physical explanations regarding the interactions between inhibitor molecules and carbon steel microstructures can also be provided with the assistance of molecular simulations.Figure caption: Contact and tapping mode AFM images of inhibitor film formed on UNS G1018 steel at 2 CMC (100ppm) tetradecyldimethylbenzylammonium inhibitor + 1 wt% NaCl. The contact mode friction image indicates a large friction contrast between inhibitor covered cementite and ferrite structure, while the tapping mode phase image indicates a negligible softness contrast between cementite and ferrite structure. Figure 1

Decreasing microbially influenced metal corrosion using free nitrous acid in a simulated water injection system

Microbially influenced corrosion (MIC) is the main cause of metal corrosion in anoxic environments. Biocides are often dosed to the corrosive media to inhibit and kill the microbes which cause MIC. In this study, intermittent dosages of free nitrous acid (FNA), which was previously found to be a biocide, were applied to a simulated water injection system containing carbon steel coupons with mature biofilm, to study the effect of FNA on mitigation of metal corrosion. In each treatment, 0.49 mg-N/L FNA was dosed using 200 mg-N/L nitrite at pH 6 for 24 h. The corrosion properties were monitored by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), 3D optical profiling, and direct weight measurement. The biofilm viability was monitored by measuring cellular ATP level. The general corrosion rate (calculated by weight-loss measurement) was decreased by up to 31%, which was supported by LPR tests and reduced ATP levels of the corrosion-inducing biofilm. The 3D optical profiling results showed that FNA decreased the average pitting corrosion rate by 59%, with 2 intermittent treatments and 82-day interval over 304 days. Intermittent dosing of FNA has strong potential to be an effective and efficient strategy for controlling MIC in oil recovery infrastructure.

Advanced Electrochemical Sensors for Monitoring Relative Humidity and Internal Corrosion Rates of Natural Gas Transmission Pipelines Containing H2s

Monitoring the internal corrosion of natural gas transmission lines is required for safe management of natural gas infrastructures. Internal corrosion programs can be strengthened by real-time monitoring of key risk factors such as relative humidity and corrosion rates of the pipeline material. We have developed a membrane-based electrochemical sensor, which functions in gaseous environments, to provide this real-time monitoring capability. The design is based on the sensitivity of the membrane’s conductivity to gaseous water content. We match relative humidity curves to 4-electrode, electrochemical impedance spectroscopy results, and use 3-electrode, linear polarization resistance tests to calculate corrosion rates. Due to the membrane’s atypical current pathways, precise estimation of the sensor’s cell constant was required to interpret the impedance results into relative humidity. We utilize finite-element analysis to obtain our cell constant (14.84 cm-1), and the resulting membrane conductivity values were in good agreement with published data. The sensor was tested in H2S environments to gauge how these results may change with acidic gases that may be present in the natural gas stream.

High Temperature Effectiveness of Ginger Extract as Green Inhibitor for Corrosion in Mild Steel

Corrosion is one of the major problems of mild steels in acidic medium. This can be minimized by the application of corrosion inhibitors, however; the most of inhibitors are toxic in nature. Therefore inhibitors from green sources are highly desirable to maintain the sustainability of the environmental system. Consequently, in this study ginger was selected; its juice extracted mechanically and used as an inhibitor. The different concentrations of ginger extract such as 0.25ml, 0.5ml, 0.75ml and 1ml were mixed in 0.1 M HCl solution to record the effect of inhibitor on corrosion rate at room temperature and at an elevated temperature of 50ᵒC. Electrochemical linear polarization resistance (LPR) tests were carried out to determine the corrosion rates at both temperatures with different additions of the inhibitor respectively. The LPR test uses three electrodes, first electrode of AISI 1019 (mild steel), second electrode is standard electrode of saturated calomel while the third electrode consists of graphite, which is called counter electrode, to measure potential difference. The whole assembly was dipped in the solution having varying concentration of inhibitors. The corrosion rate was found to be higher in the absence of ginger- extract. Conversely, the corrosion rate was dramatically reduced more prominently at 50oC but was less effective at Troom; with the trace-additions of ginger-inhibitor. So this research would be the good contribution to overcome the deterioration of mild steel and increase its life at ambient temperatures, by using economically available environmentally-friendly organic compound specially the use of locally available raw material should be focused.

Corrosion Behavior of Thermally Sprayed WC-Co-VC Coatings in NaCl Aqueous Solution

WC-17Co coatings are used to protect components against wear, high temperature and corrosion. WC based cermet coatings have been considered as alternative replacements to traditional hard chrome plating for improve surface properties of aircraft landing gear. This coatings are used in engineering applications requiring superior hardness and improved wear resistance, little is known about the corrosion resistance. In this study, four WC-17Co based composite coatings were deposited onto austenitic stainless steel substrates using high velocity oxygen fuel (HVOF) spraying at different concentrations of VC. The corrosion behavior was performed by linear polarization resistance test, potentiodynamic polarization curves and electrochemical impedance spectroscopy in saline environment. Characterization of the coating structure, morphology and composition, was carried out, prior to and after corrosion testing, using scanning electron microscopy and EDX elemental analysis. It was determined that the anodic branches present a tendency to passivation this more pronounced in sodium chloride. The results showed the addition of nanostructured WC-17Co particles improved corrosion resistance in H2O and NaCl. The addition of VC did not affect the corrosion behavior of the bimodal thermal spray coating. The electrochemical data showed that sample with 50 % of nanoparticles of WC-17Co presented higher corrosion resistance than the others in chloride solutions.

Advancing Reliability of Membrane-Based Corrosion and Environmental Sensor in Simulated Natural Gas

Monitoring simultaneously water-content and corrosion rates in low conductivity natural gas pipeline systems) is carried out using membrane-based electrochemical sensors. An ion conducting membrane improves conductivity in humid natural gas in which electrochemical measurements can be performed. In this study, we monitor corrosion rate and humidity of a gas pipeline through the use of commercial Nafion™ membranes, whose conductivity depends on the partial pressure of water vapor in the gas stream. To improve the accuracy, consistency, and reproducibility of data collection, sensor designs vary between electrode preparation using platinum wires versus nanofabricating flat electrode surfaces and configuration. Data for humidity and corrosion rates within various environments is collected using electrochemical impedance spectroscopy and linear polarization resistance tests. Data for 2-, 3-, and 4-electrode cell tests are presented to compare experimental artefacts among sensor designs.

Hexagonal Boron Nitride: The Thinnest Insulating Barrier to Microbial Corrosion.

We report the use of a single layer of two-dimensional hexagonal boron nitride (SL-hBN) as the thinnest insulating barrier to microbial corrosion induced by the sulfate-reducing bacteria Desulfovibrio alaskensis G20. We used electrochemical methods to assess the corrosion resistance of SL-hBN on copper against the effects of both the planktonic and sessile forms of the sulfate-reducing bacteria. Cyclic voltammetry results show that SL-hBN-Cu is effective in suppressing corrosion effects of the planktonic cells at potentials as high as 0.2 V ( vs Ag/AgCl). The peak anodic current for the SL-hBN coatings is ∼36 times lower than that of bare Cu. Linear polarization resistance tests confirm that the SL-hBN coatings serve as a barrier against corrosive effects of the G20 biofilm when compared to bare Cu. The SL-hBN serves as an impermeable barrier to aggressive metabolites and offers ∼91% corrosion inhibition efficiency, which is comparable to much thicker commercial coatings such as polyaniline. In addition to impermeability, the insulating nature of SL-hBN suppresses galvanic effects and improves its ability to combat microbial corrosion.

A short-term test method to determine the chloride threshold of steel–cementitious systems with corrosion inhibiting admixtures

Now-a-days, multiple types of corrosion inhibiting admixtures (CIAs) are being used to enhance the chloride threshold (Clth) of steel–cementitious systems. However, due to the application of external potential to drive chlorides, some existing short-term test methods are not suitable to assess the Clth of S–C systems with CIAs containing anions. This paper presents the development of a Modified Accelerated Chloride Threshold (mACT) test to determine the Clth for S–C systems with CIAs. The test specimens consisted of a mortar cylinder with an embedded steel piece and electrodes forming a 3-electrode corrosion cell. The specimens were exposed to chloride solution and the linear polarization resistance tests were conducted every 3.5 days. The corrosion initiation was detected using statistical analysis of the repeated R p measurements. After corrosion initiation, the chloride content in mortar adjacent to the embedded steel piece was determined and defined as Clth. The time required to complete mACT test for an S–C system with CIAs is about 120 days. The Clth of eight specimens each with S–C system containing (i) without inhibitor, (ii) anodic inhibitor [calcium nitrite] and (iii) bipolar inhibitor [both calcium nitrite and amino alcohol] were determined. Both anodic and bipolar CIAs showed enhanced corrosion resistance. Also, the bipolar inhibitor performed better than anodic inhibitor. It was concluded that the use of CIAs could significantly delay the initiation of chloride-induced corrosion. The mACT test can be used to determine the Clth and estimate the service life during the planning and design stages of a project and help select durable materials.

Statistical Distributions for the Corrosion Rates of Conventional and Prestressing Steel Reinforcement Embedded in Chloride Contaminated Mortar

Many concrete structures are built using plain mild (PM) and cold-twisted deformed (CTD) steel rebars. Also, quenched and self-tempered (QST) and prestressing (PS) steels are extensively used in today’s construction. For estimating the corrosion propagation period (tp) of concrete structures, the current practice is to assume that the corrosion rate (icorr) of different steels are equal to that of PM steel—leading to erroneous estimation of tp. This paper provides icorr data from a 33-month experiment on PM, CTD, QST, and PS steels embedded in chloride contaminated mortar. Linear polarization resistance test was adopted for icorr measurement. A total of 100 specimens were tested. It was found that the CTD and QST steels exhibit higher icorr than the PM and PS steels. The paper also provides statistical distributions for icorr of these four steels. For PM, CTD, QST, and PS steel embedded in chloride contaminated mortar, and exposed to wet-dry conditions, these are found to be ∼Weibull (2.5, 20.7, 0) μA/cm2, ∼Lognormal (0.45, 3.2, 0) μA/cm2, ∼Gamma (6.8, 3.5, 0) μA/cm2, and ∼Weibull 3P (1.3, 6.5, −0.02) μA/cm2, respectively. Similar distributions for dry condition are also presented. These statistical tools would help engineers in estimating residual service life and scheduling repair activities.

PAni/SBR composite as anticorrosive coating for carbon steel, part II: electrochemical characterization

Conducting polymer composites have gained popularity into the field of organic anticorrosive coatings research due to their low environmental and health impact. In this work, the effect of the conducting polymer/elastomer ratio and the PAni doping method on the electrochemical behavior of polyaniline/styrene butadiene rubber films (PAni/SBR) has been studied in order to evaluate the performance of the proposed coatings for carbon steel corrosion prevention. According to open circuit potential measurements, linear polarization resistance tests, electrochemical impedance spectroscopy and polarization curves, the use of dodecyl benzene sulfonic acid as doping agent and the reduction of the PAni content in the composite enhance the anticorrosive behavior of PAni/SBR composites by inducing carbon steel passivation process.

Corrosion behaviors of cement mortar specimens with different cover thickness in natural sea water

This paper presents electrochemical corrosion behaviors of cement mortar specimens in the high salinity condition. Chloride ion is known as the most detrimental parameter to cause the corrosion in reinforced concrete. Increasing the concrete cover thickness is one of the corrosion protection methods against chloride ion; so, this study mainly focuses on the effects of mortar cover thickness on corrosion protection. In specimens, rebar, which was a height of 200 mm and a diameter of 10 mm, was installed at the center of the small size form. Later on, mortar was injected into the form, and 10, 20, 30, 40, and 50 mm of the different mortar cover thicknesses were selected. Potential measurements, linear polarization resistance tests, and cyclic potentiodynamic polarization tests were performed for specimens that were exposed to seawater. These results were compared with visual inspection results of rebar. The results show that an increase in the cover thickness contributes to corrosion protection. In addition, the result of electrochemical corrosion tests generally agreed with that of an autopsy visual inspection.

Assessment of high performance concrete containing fly ash and calcium nitrite based corrosion inhibitor as a mean to prevent the corrosion of reinforcing steel

This research analyses the effectiveness of the water-to-cement ratio (w/c), fly ash and a calcium nitrite based corrosion inhibitor to prevent the corrosion of reinforcing steel embedded in high performance concrete. The interactive effect between the inhibitor and fly ash was evaluated because the occurrence of a negative effect when both ingredients are added together in a concrete mixture has been reported. All the concrete mixtures studied in this investigation had 8.2% of silica fume. Twenty seven prismatic concrete specimens were fabricated with dimensions of 55 × 230 × 300 mm each containing two steel rods embedded for the purpose of corrosion monitoring. The specimens were exposed to a simulated marine environment with two daily cycles of wetting and drying for one year. To evaluate the deterioration of the specimens corrosion potentials and linear polarization resistance tests were carried out. The results indicate that the use of a low w/c, the addition of fly ash and the addition of the corrosion inhibitor contributed to the reduction of the corrosion of steel in the concrete specimens. The results further suggest that the combination of fly ash and corrosion inhibitor does not promote the deterioration of the concrete matrix.

Comparative corrosion behaviour of different Sn-based solder alloys

Sn–Pb solders, particularly Sn–37 %Pb eutectic alloy, have been widely used as low temperature joining alloys for some time. However, the restriction of Pb use in industry has been strongly promoted to protect the environment and establishing a Pb-free solder has become a critical issue and an important task for material engineers. New solders must fulfil several requirements; in particular they must be corrosion resistant. In the present work, the corrosion behaviour of five Pb-free solders was studied in a 0.1 M NaCl aqueous solution by means of polarization measurements (corrosion potential measurements, potentiodynamic polarization curves and linear polarization resistance tests), and compare to that of a conventional Sn–37 %Pb solder alloy and pure Sn. The results show that the Sn–3.5 %Ag–0.9 %Cu, Sn–3.5 %Ag and Sn–0.7 %Cu solders have the best resistance to localized as well as to general corrosion, similar to that obtained for the Sn–37 %Pb solder and pure Sn. The Sn–57 %Bi solder has poorer corrosion properties but its behaviour is still acceptable, because it passivates and shows a relatively low corrosion rate. In all these cases the corrosion resistance is good due to the content of noble elements (Ag, Cu, Pb and Bi) in the alloys. On the other hand, the Sn–9 %Zn is definitely the one that exhibits the worst behaviour, not only to localize but also to general corrosion, due to the addition of a less noble material to the Sn matrix.

Linear Polarization Resistance Tests on Corrosion Protection Degree of Post-Tensioning Grouts

This article discusses the current industry practice for acceptance testing of post-tensioning grouts. The practice includes an accelerated corrosion test (ACT), as recommended in Post-Tensioning Institute (PTI) M55.1-03, “Specification for Grouting of Post-Tensioned Structures.” The current ACT method typically takes 1 to 2 months to complete and is seen as a downside. However, the linear polarization resistance (LPR) technique requires only a few hours to complete. The research presented in this paper indicates a strong correlation between the time to corrosion, as measured by the ACT method, and the system polarization resistance, as measured by the LPR technique. The authors recommend the use of the LPR method as a prescreen for very high-quality grouts so that lengthy ACT testing is not necessary.

Biotic Sol-Gel Coating for the Inhibition of Corrosion in Seawater

In marine environments corrosion is exacerbated by formation of destructive biofilms containing sulphate-reducing bacteria, which promote corrosion by forming corrosive species, such as H2S. Corrosion-causing biofilms are often resistant to inactivation by biocides since the biofilm bacteria are protected by a matrix of exopolymeric substances (EPS). Paradoxically, a biofilm of the endospore-forming Paenibacillus polymyxa can actually inhibit corrosion. Sol gel technology and immobilized microorganisms have been combined in a unique coating that inhibits corrosion on aluminium alloys, being low-cost, effective and environmentally friendly. Viability studies show that P. polymyxa endospores can withstand solvent concentration of up to 50% and an acid concentration of up to 1.5M and germinate within a biotic sol-gel coating. Electrochemical impedance spectroscopy and linear polarization resistance tests, in addition to an extended field trial, have shown that the endospore-loaded coatings show resistance to corrosion and biofilm formation relative to coatings without added endospores.

Corrosion performance of NiAl intermetallic with Mo, Ga and Fe in neutral and alkaline media

The corrosion resistance of mechanically alloyed NiAl intermetallics with additions of Mo, Ga and Fe, and their combinations, has been studied using potentiodynamic polarization curves and linear polarization resistance tests at room temperature. Solutions included 0.5 m NaCl and 0.5 m NaOH. The Al–42Ni+6Fe and Al–40Ni+6Fe+2Mo alloys exhibited the best corrosion resistance in NaCl whereas the highest corrosion rate was observed on Al–39Ni+6Fe+6Mo alloy, above the NiAl-base alloy. In NaOH, the highest corrosion rate was exhibited by Al–41Ni+6Mo alloy, whereas the best corrosion performance was obtained by alloys with 6Ga, followed by alloys containing 6Fe+2Ga and/or 2Mo+2Ga, and NiAl-base alloy had an intermediate corrosion rate. The alloys with the lowest corrosion rate also had the lowest pitting potential values. So, generally speaking, additions of 6Mo decreased the corrosion resistance of NiAl-base alloys in these environments. The results were supplemented by detailed scanning electronic microscopy studies and chemical microanalysis of the corroded specimens.