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  • Open access
  • 120 Reads
Initiation of chloride-induced corrosion of low carbon steel rebar in concrete using in-situ quantitative phase microscopy

Corrosion-related degradation is a major durability challenge and incurs a significant cost to civil infrastructure and society. Of crucial concern is chloride-induced corrosion of low carbon steel rebar in concrete structures. An estimated 70 to 90% of premature failures in concrete structures are caused by corrosion. From reviewing the state-of-the-art, civil engineers, materials scientists, physical metallurgists, and chemists have made considerable advancements towards understanding corrosion of steel in concrete, but many questions are still open in the understanding of chloride-induced corrosion initiation. For instance, the empirical critical chloride content for corrosion to initiate has been reported to range from 0.04% to 8.34% total chloride by weight of cement, which demonstrates the variability from research. Indeed, this range may also suggest the chloride-induced corrosion is influenced by several factors, thereby necessitating the research need to define the fundamental kinetic rate laws and mechanisms. To deal with these knowledge gaps, research around the globe is recently orienting towards methods that evaluate the corrosion kinetics and mechanisms of steel in concrete at meso-, micro-, and nanoscale. Therefore, this study presents a novel multi-dimensional experimental technique to study in situ corrosion at the nanoscale. The unprecedented scope of this study uses spectral modulation interferometry (SMI), an advanced quantitative phase microscopy technique, for real-time quantification of nanoscale surface topography evolution during corrosion to evaluate the temporally- and spatially-heterogeneous dissolution rates on a polished ASTM A615 steel surface. With a novel additive-manufactured fluid cell, experiments are performed in situ with flowing solution conditions to promote surface-controlled kinetics. Using inductively coupled plasma mass spectrometry (ICP-MS), the elemental analysis of aliquots of outflow solution from the fluid cell is evaluated, providing simultaneous, time-resolved detection and quantitative concentration measurement of the dissolved elements. Furthermore, the steel sample is connected to a potentiostat for electrochemical monitoring, allowing for a third corrosion measurement by polarization resistance. The in situ nanoscale approach of corrosion monitoring directly quantify the kinetics of corrosion, even at low chloride concentrations. Also, the integration of these techniques provide detailed quantitative and qualitative data on the corrosion mechanism and corrosion rate of ASTM A615 steel reinforcement, bringing solutions to many questions raised from the literature.

  • Open access
  • 99 Reads
Characterization of zinc phosphate coatings: influence of the pH and temperature in
morphology and corrosion resistance

Zinc phosphate coatings are commonly used to protect high-strength steel rods and improve their corrosion protection ability. The temperature and the pH of the phosphating bath are important parameters that affect the film’s appearance, porosity, and composition. In this work, several variations in the phosphating solution have been analyzed. In particular, the bath temperature was modified in the range of 50-75 °C, while the bath pH kept at 2.4, 2.8, and 3. Phosphate coatings were investigated via Scanning Electron Microscopy and Energy Dispersive X-ray that allow a complete surface analysis, including both the morphology and the composition. The coatings mass was determined by the gravimetric method. For the corrosion resistance of the film, the linear polarization curves obtained in 0.1 M Na2SO4 solution were analyzed. The results showed that the phosphating baths at 60-65ºC and pH 2.4 produced a thicker film, with the highest amount of Zn and improved corrosion resistance.

  • Open access
  • 162 Reads
The performance of the Galactomannan as a green inhibitor to protect the carbon steel against corrosion

Carbon steel suffers from high degradation in an acidic medium like acidic stripping. For this reason, the protection of the carbon steel from the aggressive acidic attacks is required. One of the most common methods of protection is the use of corrosion inhibitors. For environmental reasons, researchers have investigated a new generation of inhibitors, called green inhibitors that cause less damage to the environment while providing high protection efficiency against corrosion.

This study aims to evaluate the impact of a bio-sourced polymer as a corrosion inhibitor against iron corrosion in a 1 M HCl solution. Galactomannan was obtained from the Ceratonia Siliqua L. seeds, and its structure was characterised by using Fourier tranformation infrared spectroscopy (FTIR). Effects of the inhibitor concentration and immersion time on the corrosion resistance of iron was evaluated using different electrochemical methods (Tafel curves, impedance diagrams). Ability of the Galactomannan molecules to form links with iron atoms was characterised using UV-visible analysis. Surfaces of the corroded specimens was evaluated by using scanning electron microscopy (SEM) and EDS.

The results show that the Galactomannan acts as a mixed type inhibitor by physisorption and chemisorption on the metal surface. Besides, the efficiency of this compound increases with the concentration of the inhibitor and reaches a value of 87.72% at a concentration of 1 g/l.

  • Open access
  • 469 Reads
The corrosion behavior of 316L stainless steel additively manufactured by direct energy deposition process

Traditional additive manufacturing (AM) technologies tend to focus on powder bed fusion (PBF) methods such as SLM (Selective Laser Melting) and EBM (Electron Beam Melting), that are attractive for the rapid production of complex components. However, their inherent drawbacks include high cost of powders, high energy consumption and size limitation. Hence, more affordable and flexible direct energy deposition processes such as wire arc additive manufacturing (WAAM) are gaining increased interest. This study aims to evaluate the corrosion behavior including stress corrosion resistance of 316L stainless steel produced by the WAAM process. Experimental samples in the form of cylindrical rods were produced by WAAM process using 316L stainless steel wires and compared with its counterpart AISI 316L alloy. The corrosion resistance was evaluate using potentiodynamic polarization, impedance spectroscopy and slow strain rate testing (SSRT). Despite the differences between the microstructures of printed WAAM 316L alloy and its counterpart AISI 316L, the corrosion performance of both alloys in 3.5% NaCl solution was quite similar.

  • Open access
  • 87 Reads
On post-hydrostatic testing microbiologically influenced corrosion (MIC): causes and preventional methods

Hydrostatic testing (HYD) is a practice often applied to welded pipelines to test both the strength and the leakage (contrary to Pneumatic tests that test only leakage possibility). For most cases of HYD, seawater is a frequent option. HYD can be performed with either wrong HYD (where untreated or maltreated water is used) or as incomplete HYD (where the water used for HYD remains in the pipe or wet layup is used with untreated water). In either case, corrosion in the form of microbiologically influenced corrosion (MIC) can happen and attack weak spots such as the welding zone (HAZ). This will be leading to the loss of mechanical integrity in terms of premature failure (brittle) and leakages.

In this webinar, the main causes of post-HYD MIC and possible ways to prevent it are being discussed.

  • Open access
  • 149 Reads
Electrochemical response in biological media of plasma electrolytic oxidation treated additively manufactured Ti6Al4V alloy

Innovative 3D metal Additive Manufacturing (AM) techniques are revolutionizing the biomedical industry since they enable the production of porous structures and patient-customized parts of biomedical-grade materials, such as Ti alloys. Surface treatment via plasma electrolytic oxidation (PEO) of conventionally manufactured Ti and its alloys has been proved an outstanding approach to promote the osseointegration of implants. Henceforth, it is of increasing interest to develop PEO treatments for AM Ti alloys.

The objective of the present work was to fabricate Ca and P containing thin (~ 3 - 10 μm thickness) PEO coatings on a Ti6Al4V alloy manufactured via Direct Metal Laser Sintering (DMLS), a laser powder bed fusion AM technique, and to study the electrochemical behavior of the treated specimens in a modified α-MEM solution. The electrical response of PEO process on the AM alloy was compared to the one on wrought mill-annealed Ti6Al4V sheets. The electrochemical behavior of the PEO treated AM alloy was evaluated via potendiodynamic polarization and electrochemical impedance spectroscopy (EIS) in comparison to the non-treated AM alloy and the PEO-treated conventional counterparts. The surface degradation morphologies were evaluated by electron-optical microscopy and optical profilometry.

The effect of the AM microstructure on the PEO process and the microstructure and electrochemical response of the resultant coatings are discussed with the aim to define future work lines relevant to the improvement of the corrosion resistance of AM Ti6Al4V, particularly to pitting corrosion.

  • Open access
  • 79 Reads
Influence of waste glass powder addition in the microstructure and durability of mortars in the very long term

At present, the cement industry still constitutes an important pollutant industrial sector. Then, the strategies to reduce its environmental impact are a popular topic of research. One of these strategies consists of replacing partially clinker with other materials, such as waste glass powder. Here, it has been analyzed the effects at 1500 hardening days of the addition of glass powder on the microstructure and durability properties of mortars that incorporate 10% and 20% of this addition as clinker replacement. Reference mortars prepared with ordinary Portland cement without additions were also studied. The mortars were kept in an optimum condition (20ºC and 100% relative humidity) until the testing age. Their microstructure has been characterized using mercury intrusion porosimetry and impedance spectroscopy. As durability parameters, among others, the steady-state chloride diffusion coefficient and the absorption after immersion have been determined. According to the results obtained, mortars with glass powder showed similar porosities and more refined microstructure compared to reference mortars. Furthermore, the durability properties at 1500 hardening days of mortars which incorporate glass powder were similar or even better than those noted for reference ones without additions, especially regarding the resistance against chloride ingress, with the added value of contributing to sustainability.

  • Open access
  • 106 Reads
Risk-based inspection and maintenance planning to manage the integrity of corroded pipelines

Many pipeline operators use risk-based methods to manage the integrity of their pipeline networks. The objective is to provide an overview of state-of-the-art pipeline risk and lifecycle assessment including probabilistic modeling of inspections and corrosion growth processes. After initial construction, the total lifecycle costs of a pipeline are primarily governed by inspection and maintenance costs as well as the risk of failure. To quantify these costs, the future corrosion process needs to be modeled probabilistically and updated based on expected inspection results and repairs of the system. While corrosion rate models are preferred in practice, they do not adequately capture the temporal uncertainties of corrosion growth and should be avoided in any reliability and risk assessment. Stochastic processes better suited for uncertain corrosion growth modeling. They are inferred from pipeline inspection results where sizing errors, detection errors, and false identifications need to be considered for an accurate assessment of the uncertain state of corrosion. Using a lifecycle approach, optimal inspection and maintenance strategies are identified by minimizing the total costs under risk constraints. Examples are provided to illustrate the risk-based planning including a discussion on some current challenges.

  • Open access
  • 130 Reads
Stainless steel corrosion via direct iron-to-microbe electron transfer by Geobacter species

Microbial corrosion of iron-based materials is a substantial economic problem. A mechanistic understanding is required to develop mitigation strategies. We report here that the mechanism for microbial corrosion of stainless steel, the metal of choice for many actual applications, can be significantly different from that for Fe(0). Although H2 is often an intermediary electron carrier between the metal and microbes during Fe(0) corrosion, we found that H2 is not abiotically produced from stainless steel, making this corrosion mechanism unlikely. Geobacter sulfurreducens and Geobacter metallireducens, electrotrophs that are known to directly accept electrons from other microbes or electrodes, extracted electrons from stainless steel via direct iron-to-microbe electron transfer. Genetic modification to prevent H2 consumption did not negatively impact on stainless steel corrosion. Corrosion was inhibited when genes for outer-surface cytochromes that are key electrical contacts were deleted. These results indicate that a common model of microbial Fe(0) corrosion by hydrogenase-positive microbes, in which H2 serves as an intermediary electron carrier between the metal surface and the microbe, may not apply to the microbial corrosion of stainless steel. However, direct iron-to-microbe electron transfer is a feasible route for stainless steel corrosion.

  • Open access
  • 138 Reads
The comparison of cavitation erosion resistance of austenitic stainless steels 1.4541 and 1.4301

The one of the common causes of damage of water turbines, marine propellers, pumps or other components of hydraulic machinery, which contribute to their faster failure, is the cavitation erosion. The cause of cavitation erosion is the phenomenon of cavitation which is caused by formation and collapse of bubbles in liquids that are subjected to frequent pressure change. The cavitation erosion tests were performed in cavitation tunnel equipped with system of the barricades. The following flow velocity values were obtained: 2.30 m∙s-1, 2.49 m∙s-1, 2.67 m∙s-1 and 2.83 m∙s-1. The tested materials were two types of the austenitic stainless steels – 1.4301 and 1.4541 after heat treatment. The study compares the impact of mechanical properties, the chemical composition of steel and the flow velocity on cavitation resistance. The test results showed that steel 1.4301 had better cavitation erosion resistance than 1.4541 steel at all set flow rates. The differences in weight loss and roughness (Ra parameter) were about two times higher for 1.4541 steel compared to 1.4301steel. However, the similar mechanisms of surface degradation were observed. The conducted tests showed a significant influence of the fluid flow, chemical composition and mechanical properties on the cavitation erosion resistance.