A reinterpretation of the Romanoff NBS data for corrosion of steels in soils

Data published in the 1957 Romanoff National Bureau of Standards report for the corrosion of steels buried in soils for up to 17 years are re-interpreted using the bi-modal model for corrosion in wet environments. The relevant soil properties are those of the backfill, not those of the undisturbed soil at the depth of the steel samples. Using estimated backfill properties shows that stiff clays, calcareous loams and gravelly loams corrosion transitioned from Mode 1 to Mode 2 after 4–8 years, following severe corrosion and deep pitting. For most other backfill soils, the transition occurred later and corrosion was less severe. These differences are attributed to the relative influence of differential aeration and localised corrosion caused by air-voids at the soil–metal interface. The declining rate of corrosion in the later part of Mode 2 is attributed to backfill consolidation decreasing the diffusion of oxygen and possibly also of moisture.     

Effect of moisture content and compaction on the corrosion of mild steel buried in clay soils

ABSTRACT

The corrosion of steels in clay soils is of interest for buried steel infrastructure. To obtain better information about the early corrosion effects, mild steel coupons were exposed for 3, 6 and 13 months in finely graded clay soil at different moisture contents and with different degrees of compression to simulate compaction. It was found that the maximum corrosion mass loss and pit depths occurred at a soil moisture content of 17–18?wt-% for all exposures and levels of compaction, corresponding to around 0.65 degree of saturation. These values are broadly consistent with earlier findings for non-clay soils. For exposures of 3 months corrosion was predominantly localised but subsequently became more uniform. This was shown to be consistent with good compaction of the soil against the steel surface. Poorly compacted lumpy clays, however, showed larger areas of localised corrosion and relatively greater corrosion mass loss and deeper pitting.     

Steel corrosion in concrete: Determinist modeling of cathodic reaction as a function of water saturation degree

The prediction of the long-term behavior of reinforced concrete structures involved in the nuclear waste storage requires the assessment and the modeling of the corrosion processes of steel reinforcement. This paper deals with the modeling of the cathodic reaction that is one of the main mechanisms of steel rebar corrosion. This model takes into account oxygen reduction and oxygen diffusion through a diffusion barrier (iron oxide and/or carbonated concrete) as a function of water saturation degree. It is demonstrated that corrosion rate of reinforcement embedded in concrete with water saturation degree as low as 0.9 could be under oxygen diffusion control. Thus, transport properties of concrete (aqueous and gaseous phase, dissolved species) are key parameters that must be taken into account to model electrochemical processes on the reinforcement.     

Long-term external pitting and corrosion of buried cast iron water pipes

Improved understanding of the development with time of pitting and corrosion of the external surfaces of buried cast iron water pipes is crucial for the management of water supply distribution networks. The present study reports observations of surface topography of cast iron pipes exposed between 34 and 129 years in clay soils. Pit depths, surface areas and widths associated with deeper pits are reported, including as functions of exposure period. Pitting appears to progress in a step-wise manner as also earlier reported for the corrosion of steels. While there is a relation between pit depth and lateral size of pits through the amalgamation of pits to form plateaus into which new pits tend to form, the predominant progression of material loss through corrosion and pitting is into the metal rather than laterally. The practical implications of these observations are discussed.     

Long-term corrosion of rebars embedded in aerial and hydraulic binders - Parametric study and first step of modelling

The prediction of long-term behaviour of reinforced concrete structures involved in the nuclear industry requires a phenomenological modelling of the rebars corrosion processes. Previous analytical characterisation of archaeological artefacts allowed to identify a typical layout constituted of four layers (the metal, the dense product layer, the transformed medium and the binder). Additional experiments leaded to identify the long-term corrosion mechanisms. Following these results, this paper proposes an analytical model of long-term corrosion of rebars embedded in concrete. This modelling is considering the kinetic of oxygen diffusion through the system and its consumption at the metal/dense product layer interface as a function of concrete water saturation degree. Corrosion products thicknesses estimated with the model are then compared to corrosion product thicknesses measured on archaeological artefacts. A parametric study is performed and demonstrates that the oxygen diffusivity and the kinetic constant of the cathodic reaction affect in a wide range the model results.     

Bi-modal trend in the long-term corrosion of aluminium alloys

A wide range of literature data including in situ immersion, tidal, coastal atmospheric and industrial exposures is used to show that the trend for longer term corrosion of aluminium alloys is nearly always more consistent with a bi-modal model than with the classical power-law function. It is proposed the bi-modal characteristic results from the accumulation of corrosion products causing localised anoxic conditions. These permit a change from predominantly cathodic oxygen reduction to hydrogen ion reduction under anoxic autocatalytic conditions within pits. This mechanism is consistent with established theory for pitting corrosion in aluminium.     

Numerical modeling of high-temperature corrosion processes

Numerical modeling of the diffusional transport associated with high-temperature corrosion processes is reviewed. These corrosion processes include external scale formation and internal subscale formation during oxidation, coating degradation by oxidation and substrate interdiffusion, carburization, sulfidation and nitridation. The studies that are reviewed cover such complexities as concentration-dependent diffusivities, cross-term effects in ternary alloys, and internal precipitation where several compounds of the same element may form (e.g., carbides of Cr) or several compounds exist simultaneously (e.g., carbides containing varying amounts of Ni, Cr, Fe or Mo). In addition, the studies involve a variety of boundary conditions that vary with time and temperature. Finite-difference (F-D) techniques have been applied almost exclusively to model either the solute or corrodant transport in each of these studies. Hence, the paper first reviews the use of F-D techniques to develop solutions to the diffusion equations with various boundary conditions appropriate to high-temperature corrosion processes. The bulk of the paper then reviews various F-D modeling studies of diffusional transport associated with high-temperature corrosion.     

电缆、光缆及其材料1—3年土壤腐蚀行为

总结了全国土壤腐蚀同站7个试验站14种电缆、光缆及材料1—3年土壤腐蚀试验结果,比较了外护层材料的耐腐蚀性能.     

Inorganic,physicochemical, and microbial aspects of copper corrosion: literature survey

Abstract

A literature survey on the corrosion of copper in aqueous solutions, with particular relevance to potable water, is presented. Coverage is of inorganic and physicochemical aspects of copper corrosion, namely those dealing with the thermodynamics of copper corrosion reactions, oxygen reduction at copper surfaces, and the photoelectrochemistry of the copper-copper oxide-electrolyte, system. Microbially induced pitting corrosion and transport in associated biomembranes are also considered.     

Role of magnesium ions in reducing high temperature aqueous corrosion of carbon steel

Carbon steel is used as the primary heat transport system piping material in pressurized heavy water reactors. The carbon steel surfaces corrode during the high temperature operation. Enhanced wall thinning of the piping in locations of high velocity and neutron activation of corrosion products pose serious operational difficulties. Magnesium ion modified water chemistry resulted in significant reduction in the corrosion and corrosion release of carbon steel. The changes induced by magnesium ions in the various processes at the metal–oxide, oxide–solution interfaces, and subsequent restructuring of the oxide were identified by in situ electrochemical impedance spectroscopy.     

Post-perforation external corrosion of cast iron pressurised water mains

The corroded external surfaces of older cast iron water mains buried in soils for many decades usually show a rough undulating topography. Sometimes, there also are areas of relatively smooth topography similar to uniform corrosion but over undulating surfaces. Investigations show this pattern is associated with localised pipe-wall perforation and sometimes pipe fracture. It is proposed that corrosion pitting from the outside surface of the pipe perforates the pipe-wall, allowing fresh oxygenated drinking water from inside the pipe to effuse through the orifice. This then causes a high rate of localised general corrosion under the graphitised layer. The resulting thinning of the pipe-wall may then lead to pipe fracture under high water pressure.     

Applying Corrosion Inhibitors to Metal Surfaces in Electrostatic Field

A basically new method, not yet described in the world literature, for applying volatile corrosion inhibitors to metal surfaces in electrostatic field is suggested. The method is applicable in the corrosion protection of machinery for oil extraction and processing (gas–air zones in oil- and petroleum-storage tanks, separators, etc.), including its protection against atmospheric corrosion.     

Comparison of soil properties measurements in pipeline corrosion estimation

Soil corrosion is a hazardous electrochemical process that affects buried metals in contact with soil. Corrosion in soils resembles atmospheric corrosion with corrosion rates usually higher and depending on the soil type. There are numerous properties of soil and thus soils can be classified in many different ways. Soil resistivity is one of the main indicators of soil corrosivity and thus of the hazardous impact the soil has on metal materials in the soil environment, although it is not the only parameter affecting the risk of corrosion damage. In this study on‐site measurements and laboratory measurements of soil characteristics are performed and compared. On‐site measurements include measuring the redox potential and soil resistivity by Wenner 4‐pin method, while the measurements in the laboratory include measuring soil conductivity, as well as moisture content, pH, content of sulphates, chlorides, and sulfides and polarization measurements, which give the most accurate results. The measurements have shown that if the Wenner 4‐pin method is performed in a convenient way the obtained results are not precise but can give an indicative picture of the corrosivity of the observed soil.     

The corrosion and electrochemical behaviour of zinc in binary mixtures of dimethylformamide and water

The results of corrosion and electrochemical studies on zinc in dimethylformamide and water mixtures at 30°C indicate that the dissolution of zinc is cathodically controlled with the metal being anodically more active in the region of the higher percentage of water. Stirring and the dissolved oxygen influence only the cathodic reactions.     

The effect of atmospheric precipitation on the corrosion of ferrous metals buried in soils

Data from the US NBS study for corrosion of buried objects are employed to show that average annual atmospheric precipitation directly influences corrosion of ferrous objects buried in various soils. This is attributed to the softness of precipitation waters and their delivery of oxygen. Also, as surrogate for time of wetness at the buried object within the soil, atmospheric precipitation has a clearer effect on corrosion loss and localised corrosion than does ground surface time of wetness. The relationship and the amount of corrosion also depend on soil type, a matter not previously considered. The results allow an explanation for the generally higher rate of corrosion of cast iron water pipes in cities such as Sydney with mainly clay-loam soil backfill and high precipitation compared with many locations in the UK with much lower annual average precipitation.     

Control of local corrosion and fracture of metals in optical models of narrow crevices,gaps and cracks using ellipsometry techniques

The method of laser polarization and optical monitoring is described for model studies of distributed and localized corrosion processes in optical models of gaps and cracks. It allows studying localized corrosion fracture of a surface (crevice corrosion; pitting; corrosion cracking; galvanic, selective, intercrystallite, or microbiological corrosion; etc.) in cases in which the process is nonuniformly distributed over the surface and is inaccessible for studies using the standard corrosion–electrochemical methods.     

Empirical models for long-term localised corrosion of cast iron pipes buried in soils

ABSTRACT

Empirical models are proposed for the progression of maximum depth of localised corrosion of cast iron pipes, based on data for pipes buried in 67 different backfill clay and sandy soils for up to 129 years. Early corrosion increases with increased inhomogeneity of the backfill soil and with greater availability of free water at the soil–pipe wall interface. Longer term corrosion is correlated with free water availability and occurs at a much slower rate. In most cases, the free water is fresh, oxygenated rainwater, known to be corrosive, but may also include some groundwater. Statistical uncertainty in pit depth is estimated and factors are proposed to allow for different annual rates of precipitation.     

Studies of corrosion in power plant boiler tubes by measurement of oxygen isotopes and trace elements using secondary-ion mass spectrometry

Recent advances in secondary ionization mass spectrometry (SIMS) techniques allow the resolution of differences in the natural abundances of the isotopes of ¹⁸O and ¹⁶O, and their ratio in both conducting and insulating materials. These techniques have been used in this study to measure the oxygen isotope signatures and their spatial distribution in corrosion products formed during high-temperature oxidation of steel boiler tubes from fossil-fuel power plants. The data obtained in this study are interpreted in terms of oxygen isotope fractionation between the available oxygen reservoirs and oxides formed on or within the metal. Results are presented for three different corrosion scenarios: steamside/fireside corrosion, aqueous phosphate corrosion and corrosion due to H₂ damage. Constant, but isotopically depleted values observed in magnetites formed during steamside corrosion and H₂ damage are indicative of interaction with locally derived meteoric water (which constitutes the boiler feed water). In contrast, isotope distributions in maricite (NaFePO₄) suggest equilibrium fractionation between this phase and precursor magnetite. Oxygen isotope patterns in fireside magnetites exhibit a complex zoning that requires at least two isotopically distinct species with significantly different transport rates.     

3D Numerical modelling of steel corrosion in concrete structures

The paper deals with a 3D numerical model for transient analysis of processes after depassivation of reinforcement in concrete, which are relevant for calculation of corrosion rate. The aim of the study is to investigate the influence of the concrete quality, cracking and water saturation in concrete on the current density. The results show that the corrosion rate is higher in poor quality concrete than in good quality concrete. The model predicts that cracks do not influence corrosion rate for the case where the only influence of the crack is on the rate at which oxygen can reach the steel.