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  • Open access
  • 179 Reads
Atmospheric corrosion detection of field-exposed metallic materials by image recognition

Our group has focused on the filed corrosion detection by using image recognition in the past 30 years. Atmospheric corrosion is accompanied by the changes in surface structure, morphology, and composition. These changes can be recorded by a variety of image acquisition devices that export digital images in grayscale or true color to a detector. Information regarding corrosion type and extent can be extracted with image processing methods. Digital image processing systems used to assess material degradation are briefly illustrated, and the algorithms developed to process metallic materials degradation images are described. Future work that will augment the present methods of evaluating material degradation are discussed.

  • Open access
  • 412 Reads
Assessment of hydrogen embrittlement and a model for structural integrity analysis

Hydrogen embrittlement (HE) in a specific sense meaning can be defined as the hydrogen-caused deterioration of the mechanical properties of most metallic materials and alloys. The coexistence of different HE mechanisms and their simultaneous effects in metallic materials, including steels, is still not well documented, while recognition of the dominant mechanism, one or more, is an extremely challenging and crucial problem. A special structural integrity model was proposed [1] for analysis, prevention, and prediction of HE based on the HELP + HEDE model [2] for HE in steels. The structural integrity model corresponds with the observed coexistence of HE mechanisms (HELP + HEDE model) in metals and transition from HELP dominance to HEDE dominance at a hydrogen concentration above the critical hydrogen concentration [2,3]. The further implementation of methods for evaluation, control, and prevention of hydrogen-assisted mechanical degradation processes and HE in metals requires that the variables relevant to the application be incorporated into the basic concept that define all necessary successive steps (5-step approach) for the industrial application [2]. The global 5-step approach in assessment and prevention of hydrogen assisted mechanical degradation processes and hydrogen embrittlement in metals for the practical industrial application was proposed and consist of the following steps [3]: (1) phenomenology analysis of hydrogen-related degradation (multiscale modeling and simulation of HE phenomena); (2) hydrogen sources and entry into metal/component; (3) structural integrity (SiM) model and (4) predictive maintenance (PdM) model which should provide the basis for future (5) reliable and accurate HE damage prediction of different industrial components.

[1] M.B. Djukic, G.M. Bakic, V. Sijacki Zeravcic, A. Sedmak, B. Rajicic, Hydrogen embrittlement of industrial components: prediction, prevention, and models, Corrosion, 72 (2016), pp. 943-961.

[2] M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, Hydrogen damage of steels: A case study and hydrogen embrittlement model, Engineering Failure Analysis, 58 (2015), pp. 485-498.

[3] M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, The synergistic action and interplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity and decohesion, Engineering Fracture Mechanics 216 (2019), p. 106528.

  • Open access
  • 210 Reads
Corrosion of steel in porous media–role of the interfacial zone

The mechanism of corrosion of metals embedded in porous media is fundamentally different from corrosion of metals in bulk electrolytes. This difference is related to various aspects, including the heterogeneity found at the interfacial zone where the metal meets the porous medium, in particular the co-existence of different solid, liquid and gas phases at the metal surface. The local conditions of the interfacial zone are thus important to understand and predict corrosion of steel in porous media. This contribution reviews recent advances in the understanding of steel corrosion in porous media commonly found in the engineering context. The focus lies on steel corrosion in concrete, both with respect to localized (chloride-induced) corrosion and corrosion in near-neutral pH conditions that can be found in carbonated concrete. Recent results show that the corrosion process is governed not only by the chemistry of the liquid at the steel surface, but also by chemico-physical processes such as the interrelation of the pore structure and the exposure moisture conditions, determining the amount of liquid retained in the pores at the interfacial zone, and the transport of various species involved in the electrochemical reactions. These findings have implications for the conceptual understanding and for ensuring the durability and the sustainability of civil infrastructures in corrosive environments.

  • Open access
  • 125 Reads
Predicting environmental ageing of composites: modular approach & multiscale modelling

Fibre-reinforced composite materials are used in structural applications in marine, offshore and oil & gas industries due to their light weight and excellent mechanical properties. However, an exposure of such materials to water leads to environmental ageing, weakening the composite over time. A typical design lifetime of offshore composite structures, being in direct contact with water and humid air, spans 25 years or more. Thus, prediction and modelling of the environmental ageing phenomena becomes highly important, especially for predicting the long-term environmental durability. In this work, a systematic and modular approach for quantitatively modelling such phenomena is provided. The modular methodology presented in this work can and should be further expanded – it is multiscale and scalable. In the state-of-the-art, the degradation framework is not complete, yet it is a systematic step towards the multiscale modelling paradigm for composite materials. The topic of environmental durability of composite materials is being actively developed and is expected to continue growing also in the future.

There are 3 constituents in a composite: matrix, fibres and an interphase. Each constituent degrades differently and may also affect the degradation behaviour of each other. Therefore, a modular multiscale approach is preferred. The modules are based on the physics, chemistry of individual constituents’ interaction with the environment, including diffusion, molecular mechanisms and kinetics of environmental ageing.

The methodology is seen as a useful approach for both industry and academia, including such use cases as accelerated testing, prediction of lifetime of composite materials and structures, as well as improving understanding of the environmental ageing effects and the time-dependent properties of composites due to environmental ageing.

  • Open access
  • 123 Reads
The development, validity and applicability of integrated computational corrosion

In the last decade, integrated computation of corrosion has made significant progress towards the atomic-scale clarifying of corrosion mechanism and the computer-aided designing of advanced materials with excellent corrosion resistance. This presentation focuses on of theoretical calculation methods and developing tendency in the corrosion study, and three specific applications are presented. First-principle technique combined with molecular dynamics method, peridynamic theory and finite element method provide multiscale models to investigate the micro-mechanism of stress corrosion cracking and hydrogen-induced cracking. The calculation of passivity and passive film breakdown are discoursed elaborately through the point defects diffusion and its correlation of the energy level degeneracy. By surveying the publications, the artificial intelligence technology is pointed out how the computer can pave the way of predicting the corrosion degree as well as designing new corrosion resistant materials. To get better and efficient development of integrated computation of corrosion, extensive cooperation and powerful data infrastructure are needed by stronger joint efforts in the future.

  • Open access
  • 77 Reads
Condition-based integrity management: The convergence of inspection and assessment technologies

This paper considers integrity management (IM) based on the convergence of inspection technologies with those for defect assessment, as occurred circa 2000. Criteria to assess metal-loss severity are reviewed as a backdrop to introduce R-PCORRC, recent the reformulation of the well-known criterion PCORRC, whose reference stress now embeds a function of the strain-hardening response. Full-scale tests are introduces for Grades from Gr B up through and beyond X100 (L690) this criterion was shown accurate within 1%, with a low coefficient of variation of just 0.077. In contrast, B31G and Modified B31G showed significant bias, and scatter. The highly selective sometimes significant effect of width was shown to depend on the structural stiffness within the metal loss as compared to the stiffness of the pipe surrounding it. Defect assessment based on ILI of real corrosion was considered next, to identify technology gaps in the practical applications of this technology. It was apparent that improvements in MFL signal interpretation will help to resolve the issues with boxing criteria. The need for and benefits of accurate precise predictive schemes for metal-loss severity are illustrated as the basis to show that a conservative prediction of failure pressure gives rise to a non-conservative prediction of defect size, leading to a non-conservative re-inspection interval for a pipeline. Finally, it was also shown that using an accurate scheme can result in significantly reduced maintenance, with a related benefit in a reduced scope of field digs to demonstrate the viability of inspection-based IM.

  • Open access
  • 133 Reads
Influence of nitrogen addition and dissolved oxygen on the passivation of cantor high entropy alloy in sulfuric acid

In this work, elementally resolved electrochemical technique, namely atomic emission spectroelectrochemistry (AESEC), was used to probe the fate of elements during passivation of the Cantor high entropy alloys. Specially attention was paid on the effect of nitrogen addition and the dissolved oxygen on the elemental behavior. It was found that passivation of the Cantor alloys was a selective dissolution (incongruent dissolution) process with Cr primarily enriched on the surface. The addition of nitrogen improved the passivation proficiency by reducing the active dissolution prior to passivation. As a result, the Cantor-N alloy with added nitrogen was found to spontaneously passivate at the open circuit potential (Eoc) after the passive film was compromised. Spontaneous passivation involved surface enrichment of Cr as well as Mn to a lesser degree. It was posited that N bonded with Cr in the Cantor-N alloy formed the interstitial compound CrN that is highly resistant to dissolution and is capable of transforming to Cr oxide at the active potential.

Dissolved oxygen increased anodic dissolution during Eoc for Cantor alloy but improved the passivity for Cantor-N alloy. This phenomenon was explained using the elementally resolved polarization curve. Dissolved oxygen also improved the anodic passivation for both alloys. The specimens passivated at a constant anodic potential in the oxygenated electrolytes showed lower dissolution as compared to their counterparts passivated in aerated and deaerated solutions. Oxygen is therefore suggested to be a more efficient passivating agent as compared to water at sufficiently high anodic potential.

  • Open access
  • 312 Reads
Impact of radiation on corrosion and SCC of austenitic stainless steels

Radiation affects both corrosion and stress corrosion cracking of stainless steels in high temperature water. While a general understanding of the processes is emerging, there are several interesting observations that have yet to be incorporated. Under irradiation, metal loss both by dissolution and oxide formation is reduced compared to the non-irradiated condition. Both radiolysis and radiation damage in the metal play a role in this observation. Regarding SCC, it is now known that the local stress at the grain boundaries at sites of dislocation channel impingement plays a critical role, as does the composition of the surface oxide over the grain boundary. Emerging factors include grain boundary migration and oxidation down the grain boundary. Other factors such as the presence of second phases near grain boundaries and the overall composition of the steel can significantly affect the cracking susceptibility. Still, the low percentage of cracked boundaries suggests additional factors not accounted for. This talk will focus on what is known and what remains to be discovered on the role of irradiation in corrosion and stress corrosion cracking.

  • Open access
  • 157 Reads
Generic relations between degree of saturation of concrete, resistivity and corrosion rate

The initial measurements with linear polarization technique on steel embedded in concrete show immediately that the controlling parameter of the corrosion rate value is the degree of saturation, as it controls the concrete resistivity. In present paper is given some old values and those found in specimens exposed to the atmosphere and rain during more than 25 years. The results show the importance of the degree of saturation, but also the fact that it is irregular in the cover depth as the rain penetrates by capillarity and takes some days to reach the bar surface with a cover depth of 3 cm. This fact of the gradient of humidity in the concrete surface is one of the reasons of the dispersion when the degree of saturation of the bulk resistivity is represented with respect to the corrosion rate. Also are commented the expression of the moisture content as volumetric fraction instead as water saturation degree. Average values and standard deviations are commented as well as some simplified equations for the calculation of the corrosion rate from the degree of saturation.

  • Open access
  • 138 Reads
Degradation of sputtered hydroxyapatite in different acellular media

The aim of the present paper is to demonstrate the influence of Ag addition on in vitro bioactivity and degradation properties of sputtered hydroxyapatite in three acellular media: simulated body fluid (SBF), Dulbecco's Modified Eagle's medium (DMEM) and phosphate buffer solution (PBS). The immersion tests were performed at 37°±0.5°C during a period ranged from 1 to 21 days. The coatings were achieved by a RF-magnetron sputtering method using two cathodes manufactured of hydroxyapatite and one made of Ag (99.9% purity). The EDS analysis demonstrated that the deposited coatings were mainly composed of calcium and phosphorus, their ratio was ranged from 1.69 to 1.71. The in vitro behaviour in SBF, DMEM and PBS media has indicated that Ag doped coatings are more resistant to corrosion of SBF and PBS, while in DMEM is very similar to the undoped hydroxyapatite costings.

The work was supported by the grant of the Romanian National Authority for Scientific Research and Innovation, CCCDI – UEFISCDI, projects number COFUND-ERANET-RUS-PLUS- CoatDegraBac no.68/2018, within PNCDI III, as well the Core Program no. 18N-01--02/2019) and no. 19PFE/October 17, 2018 PROINSTITUTIO.