Severe Localized Corrosion Research Articles

The study on the influence of aluminum on the CO2 corrosion resistance of 3%Cr steel

PurposeThis study aims to report the CO2 corrosion performance of 3Cr steel and 3Cr2Al steel and reveal the role of aluminum in mitigating corrosion of low-Cr steel.Design/methodology/approachAluminum was added to 3Cr steel to prepare a new type of 3Cr2Al steel, and the effect of aluminum on the corrosion resistance of pipeline steel was studied using morphology observation and composition analysis, weight loss tests and electrochemical test.FindingsIn the CO2/O2 coexistence environment, the average corrosion rate of the 3Cr2Al steel was obviously lower than that of the 3Cr steel. The addition of aluminum expanded the range of prepassivation, and the dynamic potential polarization curve of 3Cr2Al steel showed duplex prepassivation phenomena. 3Cr steel underwent severe local corrosion, and 3Cr2Al steel underwent uniform corrosion. The addition of aluminum contributed to the formation of a dense corrosion product layer and greatly reduced the localized corrosion sensitivity.Originality/valueThe studies on CO2 corrosion of aluminum containing low-Cr steel are quite rare. This study clarifies the role of aluminum by comparing the corrosion behavior of 3Cr2Al and 3Cr steel. The effect of aluminum on the growth of corrosion product film was discussed, and the duplex prepassivation phenomena of Cr and Al were revealed.

Revisiting the tolerance limit of Fe impurity in biodegradable magnesium

The existence of iron impurity in magnesium (Mg) is conventionally deemed detrimental to the corrosion resistance against the inorganic solutions, especially over its tolerance limit. We deliberately investigated the biodegradation properties of pure Mg with different contents of Fe by immersing in DMEM+10% FBS. Surprisingly, the impurity of Fe, even its content higher than the tolerance limit previously determined by immersion in inorganic solutions such as NaCl, has no negative effect on the degradation of pure Mg. Pure Mg with a high content of Fe impurity even retains good biocompatibility. Detailed microstructural analyses decipher that the severe local micro-galvanic corrosion caused by the Fe impurity meanwhile promotes the formation of compact Ca-rich corrosion product layer on the top surface, protecting the adjacent Mg matrix from being further corroded. The present discovery provides new insights in designing biodegradable Mg alloys, especially pursuing high-level impurity doping without deteriorating the biocompatibility.

COMPREENDENDO OS MECANISMOS DE CORROSÃO DE LIGAS DE Al-Cu-Li: UMA INVESTIGAÇÃO ATRAVÉS DE TÉCNICAS ELETROQUÍMICAS GLOBAIS E LOCAIS

ON THE CORROSION MECHANISMS OF Al-Cu-Li ALLOYS: AN INVESTIGATION USING GLOBAL AND LOCAL ELECTROCHEMICAL TECHNIQUES. In this study, the corrosion mechanism of an Al-Cu-Li alloy manufactured by two different treatment routes (T3 and T851) was evaluated by immersion and electrochemical tests in solutions containing chloride ions (Cl-). For both alloys, the formation of cavities on the surface was associated with micrometer-sized intermetallics (IM’s), however, in addition to this attack, the alloy submitted to T851 treatment also presented an attack called severe localized corrosion (SLC), caused by the preferential attack to the nanometric T1 (Al2CuLi) phase. The electrochemical concepts involved in these two types of attacks were discussed. During the IM’s corrosive process, whereas the O2 reduction occurred over the IM’s, the Al dissolution is favored around the particle, forming trenching and cavities (with 2 and 6 mm of depth). On the other hand, the mechanism associated with the SLC is related to the formation of a differential aeration cell followed by the evolution of H2, with greater depth of attack penetration (8 and 35 mm). Additionally, by the use of the Scanning Vibrating Electrode Technique (SVET), it was concluded that the higher anodic currents observed for the T851 temper were related to the relation between the anodic area (Aa) and the cathodic area (Ac).

The Corrosion Process of an API 5L X80 Welded Joint in a System with Different pH and H2S Concentration

The corrosion evaluation of steels in the oil and gas industry environments is a crucial issue because corrosion can cause economic and human losses. It is well known that H2S can be originated from different processes in the oil and gas industry, accelerating the corrosion process. The objective of this work was to evaluate the H2S corrosion resistance of an API 5L X80 steel and its welded joint obtained by submerged arc welding process (SAW). All tests were performed in an aerated 5% wt NaCl and thiosulphate aqueous solution. The H2S concentration, pH, weight loss, electrochemical tests, and microstructure were considered. The results obtained showed an increase of the corrosion rate values, with decreasing pH and increasing concentration of H2S generated by the thiosulphate. For the lowest H2S concentrations, the corrosion process was inhibited, due to the formation of a partially protective film on the samples’ surfaces. The heat affected zone (HAZ) showed severe localized corrosion attack which was attributed to the microstructural characteristics of this region.

Simultaneous enhancement of mechanical properties and corrosion resistance of as-cast Mg-5Zn via microstructural modification by friction stir processing

Magnesium alloys are ideal lightweight materials; however, their applications are extremely limited due to their low strength, poor ductility, and weak corrosion resistance. In the present study, a friction stir processing (FSP) treatment was employed to optimize the mechanical properties and corrosion resistance of an as-cast Mg-5Zn alloy. The average grain size of the Mg-5Zn alloy was refined from 133.8 µm to 1.3 µm as a result of FSP. Along different directions, FSP exhibited the enhancement effects on different mechanical properties. Furthermore, according to the potentiodynamic polarization results, the corrosion current density at the free-corrosion potential of the FSPed sample, was 4.1 × 10−6 A/cm2 in 3.5 wt.% NaCl aqueous solution, which was significantly lower than that of the as-cast sample. Electrochemical impedance spectroscopy revealed that the polarization impedance, Rp, of the FSPed sample was 1534 Ω/cm2 in 3.5 wt.% NaCl aqueous solution, which was 71.4% greater than that of the as-cast sample. The corrosion morphology of the FSPed sample in 3.5 wt.% NaCl aqueous solution exhibited largely uniform corrosion, rather than severe localized corrosion characteristics, which further reduced the corrosion depth on the basis of reducing the corrosion current density. The results presented herein indicate that FSP is a viable technique for simultaneously improving the mechanical properties and corrosion resistance of the as-cast Mg-5Zn alloy.

Impact of sterilization treatments on biodegradability and cytocompatibility of zinc-based implant materials

Biodegradable zinc (Zn) and Zn-based alloys have been recognized as promising biomaterials for biomedical implants. Sterilization is an essential step in handling Zn-based implants before their use in clinical practice and there are various sterilization methods are available. However, how these treatments influence the Zn-based biomaterials remains unknown and is of critical relevance. In this study, three commonly-applied standard sterilization methods, namely gamma irradiation, hydrogen peroxide gas plasma and steam autoclave, were used on pure Zn and Zn3Cu (wt%) alloy. The treated Zn and ZnCu alloy were investigated to compare the different influences of sterilizations on surface characteristics, transient and long-term degradation behavior and cytotoxicity of Zn and Zn alloy. Our results indicate that autoclaving brought about apparently a formation of inhomogeneous zinc oxide film whereas the other two methods produced no apparent alterations on the material surfaces. Consequently, the samples after autoclaving showed significantly faster degradation rates and more severe localized corrosion, especially for the ZnCu alloy, owing to the incomplete covering and unstable zinc oxide layer. Moreover, the autoclave-treated Zn and ZnCu alloy exhibited apparent cytotoxic effects towards fibroblasts, which may be due to the excessive Zn ion releasing and its local concentration exceeds the cellular tolerance capacity. In contrast, gamma irradiation and hydrogen peroxide gas plasma had no apparent adverse effects on the biodegradability and cytocompatibility of Zn and ZnCu alloy. Our findings may have significant implications regarding the selection of suitable sterilization methods for Zn-based implant materials among others.

Corrosion behavior of X80 pipeline steel in oilfield injection water in Eastern China

PurposeThis paper aims to under the laboratory environment, the corrosion behavior of X80 pipeline steel in oilfield injection water in eastern China was studied by immersion test.Design/methodology/approachFirst, the corrosion product film was immersed in oilfield injection water and the effect on the corrosion behavior and the corrosion reaction mechanism were constantly observed during this period. The effect was displayed by potentiodynamic polarization curve and electrochemical impedance spectrums (EIS) measurements. Second, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to observe and test the corrosion product film immersed in the oilfield water for 30 days.FindingsThe results indicate that the tendency of metal corrosion becomes weaker at an early stage, but strengthened later, which means the corrosion rate is accelerating. Besides, it is indicated by impedance spectroscopy that with the decreasing of the capacitance arc radius, the reaction resistance is reducing in this progress. Meanwhile, the character of Warburg impedance could be found in EIS, which means that the erosional components are more likely to penetrate the product film to reach the matrix. The corrosion product is mainly composed of the inner Fe3O4 layer and outer shell layer, which contains a large number of calcium carbonate granular deposits. It is this corrosion under fouling that produces severe localized corrosion, forming many etch pits on the metal substrate.Originality/valueThe experiment chose the X80 steel, the highest-grade pipeline steel used in China, to conduct the static immersion test in the injection water coming from an oilfield in eastern China. Accordingly, the corrosion mechanism and the effect of corrosion product film on the corrosion of pipeline steel were analyzed and discussed.

Effect of heat treatment on microstructure and corrosion behavior of Mg-5Al-1Zn-1Sn magnesium alloy

The effects of heat treatment on the microstructure and corrosion behavior of AZT511 magnesium alloy were investigated by microscopic analyses, immersion tests, and electrochemical measurements. The results showed that AZT511 alloy has well corrosion resistance, as the alloy showed filamentous local corrosion after immersed for 7 days. The oxide film of T4 alloy effectively prevented corrosion in the initial stage, but severe local corrosion occurred after a long-term immersion. T6 alloy had numerous local micro-galvanic corrosion originated by second phase in the initial corrosion. While a long-term immersion, it had the lowest corrosion rate as the small corrosion driving force.

Evading strength-corrosion tradeoff in Mg alloys via dense ultrafine twins

Conventional ultrafine-grains can generate high strength in Mg alloys, but significant tradeoff of corrosion resistance due to inclusion of a large number of non-equilibrium grain boundaries. Herein, an ultrafine-grain structure consisting of dense ultrafine twins is prepared, yielding a high strength up to 469 MPa and decreasing the corrosion rate by one order of magnitude. Generally, the formation of dense ultrafine twins in Mg alloys is rather difficult, but a carefully designed multi-directional compression treatment effectively stimulates twinning nucleation within twins and refines grain size down to 300 nm after 12-passes compressions. Grain-refinement by low-energy twins not only circumvents the detrimental effects of non-equilibrium grain boundaries on corrosion resistance, but also alters both the morphology and distribution of precipitates. Consequently, micro-galvanic corrosion tendency decreases, and severe localized corrosion is suppressed completely. This technique has a high commercial viability as it can be readily implemented in industrial production.

Corrosion resistance and conductivity of amorphous carbon coated SS316L and TA2 bipolar plates in proton-exchange membrane fuel cells

Metal bipolar plates (BPs) typically corrode and form a high-resistivity passivation film in the environment of proton-exchange membrane fuel cells (PEMFCs). Surface modification is urgently needed to improve the corrosion resistance and surface conductivity of metal BPs, and their performance is typically closely related to the substrate type and coating characteristics. In this work, the commonly used metal BP substrates SS316L and Grade 2 Titanium (TA2) were selected, and an amorphous carbon (α-C) film was prepared using DC balanced magnetron sputtering. The passivation film defect density and corrosion resistance of SS316L and TA2 were analyzed by electrochemical and Mott–Schottky tests. The influence of the type of substrate on the microscopic morphology and phase composition of the α-C film was systematically studied, and the corrosion resistance, high-potential (1.4 V (SCE)) corrosion, and surface contact resistance of the film were also analyzed. It was found that the film has excellent corrosion resistance at 0.6 V. However, at 1.4 V (SCE), the film on SS316L showed severe local corrosion, while the TA2 sample did not show any local corrosion. This demonstrates that the corrosion resistance of the BPs is dominated by the film at 0.6 V; while at high corrosion potentials, the corrosion resistance of the substrate plays a decisive role.

In vitro corrosion properties of HTHEed Mg-Zn-Y-Nd alloy microtubes for stent applications: Influence of second phase particles and crystal orientation

Magnesium (Mg) alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability. However, in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer from a rapid corrosion rate and severe localized corrosion, which is limiting their widespread application. To solve the problem of uneven degradation of stents, a HTHE (long-time and high-temperature heat treatment, large-reduction-ratio hot extrusion) process is used to manufacture Mg-Zn-Y-Nd alloy microtubes in this study. The heat treatment is to dissolve alloying elements and reduce the size of SPPs, and the hot extrusion is to acquire fine-grained and strongly textured microtubes. The microstructural characterization shows that coarse second phases in as-cast alloy are refined and uniformly distributed in matrix of microtubes. After hot extrusion, microtubes show strong texture with basal plain oriented parallel to the longitudinal section (LS). The corrosion testing indicates that severe localized corrosion occurs on the cross section (CS) while localized corrosion is alleviated on the LS. Based on the different corrosion properties of the LS and CS, HTHEed microtubes are promising for solving the problems of rapid corrosion rate and severe localized corrosion of Mg alloy stents.

Strain-Aging-Assisted Localized Corrosion of a Mill-Scaled X-65 Pipeline Steel

This investigation was designed to study whether strain aging could assist localized corrosion of pipeline steels under realistic conditions, which is an unsolved problem in the evaluation of strain-aging-induced stress corrosion cracking of pipeline steels in the field. It was found that the corrosion severity was significantly aggravated after strain aging because of the increase in yield strength and the transformation of oxide scales on the steel surface. These variations caused by strain aging lead to lesser exfoliation and longer life of the oxide scales under cyclic loading in air and during subsequent corrosion exposure, which enhances the galvanic corrosion between oxide scales and the steel substrate. The composition of oxide scales, mechanical properties of steels, and magnitude of the stress cycles, which could all impact localized corrosion, were studied. The findings of this investigation suggest that the severe localized corrosion leading to crack initiation is a vital factor for the higher SCC susceptibility of pipeline steels associated with strain aging, in addition to the enhanced hydrogen embrittlement as usually believed.

The influence of Ga, Sn, or Bi addition on the electrochemical behavior and discharge performance of Al–Zn–In anodes for Al-air batteries

In this work, experimental methods, such as electrochemical measurements, hydrogen collection technique, battery performance tests, and microstructure analysis, are used to investigate the electrochemical properties and discharge behaviors of Al–4.5Zn–0.05In and Al–4.5Zn–0.05In–0.05Ga/Sn/Bi anodes in 4 M NaOH solutions. Results suggest that the discharge performance of Al–Zn–In anodes can be further enhanced by adding Ga, Sn, or Bi elements. These elements show a dissolution-deposition behavior on the anode surface, which reduces the resistance of the passive film and increases the activity of active sites on the electrode surface. Also, adding Sn or Bi works better than adding Ga. Because Ga element is likely to cause severe local corrosion at the grain boundaries. Furthermore, the peak energy densities of Al–4.5Zn–0.05In–0.05Sn and Al–4.5Zn–0.05In–0.05Bi anodes at 40 mA cm−2 are approximately 3628.64 Wh kg−1 and 3456.12 Wh kg−1, respectively, which are 29.6% and 23.5% higher than that of Al–4.5Zn–0.05In anodes.

How microstructure affects localized corrosion resistance of stir zone of the AA2198-T8 alloy after friction stir welding

In this study, the microstructure and corrosion resistance of the stir zone (SZ) of the AA2198-T8 Al-Cu-Li alloy welded by friction stir welding (FSW) were investigated by microscopy, immersion tests and electrochemical techniques such as measurements of open circuit potential variation with time, and scanning vibrating electrode technique (SVET) measurements. A low chloride-containing solution (0.005 mol L−1 NaCl) was employed in the corrosion studies and severe localized corrosion (SLC) was observed in the SZ related to intergranular attack. The results were compared to those of the non-affected areas by FSW, also known as base metal (BM). In the BM, SLC was found and the type of attack related to it was intragranular. In both zones, BM and SZ, SLC was due to precipitates of high electrochemical activity, specifically T1 (Al2CuLi) phase in the BM, whereas TB (Al7Cu4Li) / T2 (Al6CuLi3) in the SZ. Scanning vibrating electrode technique (SVET) analysis was very useful in the study of SLC in the AA2198-T8 alloy showing the development of high anodic current densities at the mouth of the SLC sites.

Long-Term Corrosion Behavior of AZ80 Magnesium Alloy along Different Crystallographic Orientations in Simulated Body Fluid

Two orientation samples were prepared along the normal (ND) and transverse (TD) directions of the rolled AZ80 magnesium alloy. The samples (ND and TD) were immersed in simulated body fluid (SBF) for long-term (25 days) immersion test. Electrochemical measurements such as electrochemical impedance spectroscopy and potentiodynamic polarization test were conducted to study the electrochemical behavior. Scanning electron microscopy and energy-dispersive x-ray spectrometer were used to investigate the corrosion morphology and chemical composition of samples during various immersion processes. X-ray diffraction was employed to identify the texture composition. The results indicated that severe localized corrosion occurred in the ND sample. Uniform corrosion was the dominant corrosion in the TD sample. The TD sample exhibited better corrosion performance (higher corrosion resistance and lower corrosion rate) than the ND sample. The corrosion behavior of magnesium alloy was closely related to texture, microstructure, and corrosion product film. The influence mechanism of texture and microstructure on corrosion behavior of magnesium alloy was discussed.

Use of Amperometric and Potentiometric Probes in Scanning Electrochemical Microscopy for the Spatially-Resolved Monitoring of Severe Localized Corrosion Sites on Aluminum Alloy 2098-T351.

Amperometric and potentiometric probes were employed for the detection and characterization of reactive sites on the 2098-T351 Al-alloy (AA2098-T351) using scanning electrochemical microscopy (SECM). Firstly, the probe of concept was performed on a model Mg-Al galvanic pair system using SECM in the amperometric and potentiometric operation modes, in order to address the responsiveness of the probes for the characterization of this galvanic pair system. Next, these sensing probes were employed to characterize the 2098-T351 alloy surface immersed in a saline aqueous solution at ambient temperature. The distribution of reactive sites and the local pH changes associated with severe localized corrosion (SLC) on the alloy surface were imaged and subsequently studied. Higher hydrogen evolution, lower oxygen depletion and acidification occurred at the SLC sites developed on the 2098-T351 Al-alloy.

On the local corrosion behavior of coupled welded zones of the 2098-T351 Al-Cu-Li alloy produced by Friction Stir Welding (FSW): An amperometric and potentiometric microelectrochemical investigation

Localized electrochemical methods supported by surface analytical characterizations were employed to investigate galvanic coupling effects and local electrochemical activity developed along the welded zones in Friction Stir Welded 2098-T351 Al-Cu-Li alloy. The investigation was carried out in the coupled weld joint/heat affected zones (WJ/HAZ) for both, the retreating (RS) and the advancing (AS) sides. The correlation between the surface chemistry, the microstructural characteristics and the electrochemical activity of these welded areas was studied. The results showed the development of galvanic interactions within and between the WJ and HAZ regions, which were imaged using the scanning vibrating electrode technique (SVET), and scanning electrochemical microscopy (SECM). SVET analyses showed that HAZ was more susceptible to the development of anodic sites than WJ. SECM in amperometric operation mode showed that WJ coupled to HAZ exhibited higher oxygen consumption and higher cathodic activity compared to HAZ. Furthermore, SECM in potentiometric operation showed alkalinization around WJ and increased acidity in HAZ, mainly at sites of severe localized corrosion (SLC). Based on the SVET and SECM results in combination with the surface analyses, it is proposed that the microgalvanic cells formed within these welded zones are due to the presence of secondary phases in the 2098-T351 alloy and their interactions with the adjacent matrix.

Time-dependent corrosion behavior of electroless Ni–P coating in H2S/Cl− environment

As a mature technology, electroless Ni–P alloy coating is widely applied in the protection of chemical equipment and pipelines owing to its excellent corrosion resistance, but its application and long-term service evaluation in the field of high-sulfur oil and gas are rare. Therefore, the time-dependent corrosion behavior of Ni–P coating, which was plated on the L360 steel surface, was investigated in a saturated H2S medium by the method of surface analysis. The results indicate that Ni–P coating with a thickness of about 52.6 μm could significantly reduce the corrosion rate compared with uncoated pipeline steel. This is related to the structure of the dense, protective film on the surface. The uncoated pipeline steel suffered local corrosion during the immersion process, and then it developed into uniform corrosion with the formation of a large number of corrosion products. In comparison, Ni–P coatings corroded relatively mildly with only a thin corroded layer. However, during prolonged corrosion testing, the corrosive medium penetrated the coating/substrate interface at inherent defects, leading to severe local corrosion of the substrate.

Influence of chloride ions concentration on the development of severe localised corrosion and its effects on the electrochemical response of the 2198-T8 alloy

ABSTRACT The development of severe localised corrosion (SLC) on the 2198-T8 alloy was investigated in solutions of various NaCl concentrations (0.001, 0.005 and 0.01 mol L−1). Immersion tests, optical profilometry, conventional and local electrochemical analyses were performed to evaluate the corrosion behaviour of the alloy. Immersion tests showed that the alloy is susceptible to SLC in all conditions, although the pits sizes were dependent on the solution concentration. The largest anodic areas, corresponding to SLC sites, were observed for the sample immersed in 0.001 mol L−1 NaCl, whereas pits with similar sizes were observed for the samples immersed in solutions with 0.005 and 0.01 mol L−1 of NaCl. Moreover, the maximum depth of attack was observed for the sample immersed in 0.001 mol L−1 NaCl. These results were in agreement with the scanning ion-selective electrode technique (SIET) maps which showed stronger acidification on the sample exposed to 0.001 mol L−1 NaCl solution.

Ultimate Strength of Hull Structural Stiffened Plate with Grooving Corrosion Damage under Uniaxial Compression

Grooving corrosion results in a decrease in the ability of the structure to resist external loads. In the present study, a new assessment method was developed to investigate the ultimate loading capacity of stiffened plates with grooving corrosion damage. First, the basic parameters of stiffened plates (including model range, boundary condition, welding residual stress, initial geometric imperfection, and size of finite element) were assumed. Second, the influences of corrosion parameters and geometrical parameters of stiffened plates (such as finite element type, groove width, groove depth, groove depth-to-width ratio, plate flexibility, stiffener flexibility, and number of stiffeners) were analyzed. Third, based on the data analysis from a large number of nonlinear finite element analyses, the ultimate strength reduction formula of stiffened plates was derived. Last, the correctness of the formula was verified by ultimate strength experiment. Introduction Ships are always in the harsh marine environment, and it would inevitably be corroded. The existence of corrosion would reduce the effective thickness of structures and promote the generation of fatigue cracks, brittle failure, and instability damage. Grooving corrosion is a major corrosion form leading to structural failure of the hull structure (Zhang et al. 2017b). Therefore, it is very important to study the ultimate loading capacity of corroded structures to ensure the safety during the total expected life cycle. Corrosion mainly included uniform corrosion and local corrosion. Local corrosion (such as pitting corrosion and grooving corrosion) was relatively complex. For local corrosion, complex corrosion status appears on the surface of the hull structure. Sultana et al. (2015) analyzed the effect of random pitting on the ultimate compressive strength of plates and stiffened plates. They found that the volume loss caused by corrosion resulted in a significant reduction in the ultimate strength of plates, up to 45%, compared with stiffened plates. Huang et al. (2017) derived the ultimate strength reduction formula of pitted stiffened plates by analyzing a large number of nonlinear finite element analysis (FEA) data. Woloszyk et al. (2018) studied the effect of severe local corrosion damage on the strength capacity of stiffened panels by combining finite element with experimental. They found that corrosion not only reduces the thickness of the structure but also increases the surface roughness and affects the mechanical properties.