Role of sulphate ions on the formation of calcareous deposits on steel in artificial seawater; the formation of Green Rust compounds during cathodic protection

Barchiche, C.; Deslouis, C.; Gil, O.; Joiret, S.; Refait, Philippe; Tribollet, Bernard

doi:10.1016/j.electacta.2009.01.023

Cited by 62 publications

(36 citation statements)

References 34 publications

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“…The layers (region 1 in Figure 8) are clearly Mg-rich with the lighter contrast areas (region 2 in Figure 8) and Ca-rich with the fine layer at the metal surface a combination containing both Ca and Mg. The coating consists of a fine layer of a mixture of Ca and Mg, followed by a predominantly brucite coating; this is contrary to others findings of the two layer structure of a fine brucite layer followed by CaCO3 [7,14,16,17,[19][20][21]. Figure 9.…”

Section: Compositioncontrasting

confidence: 53%

“…In previous studies it has been established that the deposit has a two layer structure made up of a fine layer of Mg-rich brucite followed by a Ca-rich polymorph [7,14,[16][17][18][19][20][21]. Leeds and Cottis [22] found that a CaCO3 only deposit occurred at a potential of −0.7 V (SCE) and Barchiche et al [19] suggested an aragonite deposit would be formed at a potential −0.9 ≤ E ≤ −1.1 V (SCE), a combination of aragonite and brucite at −1.2 V (SCE) with brucite the only phase forming at a potential more negative than −1.3 V (SCE) in the 10-30 °C range with rotating electrodes.…”

Section: Introductionmentioning

confidence: 99%

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Natural Deposit Coatings on Steel during Cathodic Protection and Hydrogen Ingress

Smith

Paul

2015

Coatings

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Abstract:The calcareous coating formed during cathodic protection (CP) in seawater is known to reduce the current demand by hindering the transport of species required to support the cathodic reactions and, thereby, improve the economic performance of CP systems. There is, however, uncertainty as to whether the coating reduces hydrogen uptake or indeed enhances it. To ascertain this, two sets of samples were polarized at −1.1 V (standard calomel electrode, SCE) in 3.5% w/v NaCl and synthetic seawater (ASTM D1141) at 20 °C and the diffusible hydrogen content measured over a period of 530 h. Under such conditions reports suggest a deposit with two distinct layers, comprising an initial brucite layer followed by an aragonite layer. Contrary to other findings, a fine initial layer containing Ca and Mg followed by a brucite layer was deposited with a few specks of Ca-containing zones in synthetic seawater. The hydrogen uptake was found to occur within the initial 100 h of exposure in synthetic seawater whilst it continued without the benefit of a deposit coating, i.e., in 3.5 wt % NaCl solution.

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Section: Compositioncontrasting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Natural Deposit Coatings on Steel during Cathodic Protection and Hydrogen Ingress

Smith

Paul

2015

Coatings

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“…Additionally, like paints, they are thought to have an increased ionic resistance and to afford some degree of resistance inhibition. A considerable amount of work has already been done in understanding the mechanism formation of calcareous deposits and factors influencing this formation [2][3][4][5][6][7][8][9][10][11][12][13][14]. However, the effects of corrosion and the development of corrosion products under cathodic protection are reported sporadically [8,9].…”

Section: Introductionmentioning

confidence: 99%

A Study of Calcareous Deposits on Cathodically Protected Mild Steel in Artificial Seawater

Yang

Scantlebury

Королева

2015

Metals

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Calcareous deposits were formed on steel under conditions of cathodic protection in artificial seawater at applied constant current densities ranging from 50 to 400 mA·m −2. The calcareous layers were characterized using a Field Emission Gun Scanning Electron Microscope (FEG SEM) in conjunction with Energy Dispersive X-Ray Analysis (EDX), and Electrochemical Impedance Spectroscopy (EIS). At cathodic current densities of 50-100 mA·m −2 where corrosion was still occurring, a clear correlation existed between the iron containing corrosion product and the overlying magnesium hydroxide layer. This revealed that the mapping of magnesium rich areas on a steel surface can be used in the identification of local corrosion sites. At current densities of 150-200 mA·m −2 , a layered deposit was shown to occur consisting of an inner magnesium-containing layer and an outer calcium-containing layer. At current densities of 300-400 mA·m −2 , intense hydrogen bubbling through macroscopic pores in the deposits gave rise to cracking of the deposited film. Under such conditions deposits do not have a well-defined double layer structure. There is also preferential formation of magnesium-rich compounds near the steel surface at the early stages of polarisation and within the developing pores and cracks of calcareous deposits later on. Based on SEM/EDX investigation of calcareous depositions the impedance model was proposed and used to monitor in situ variations in steel corrosion resistance, and to calculate the thickness of formed deposits using the length of oxygen diffusion paths. OPEN ACCESSMetals 2015, 5 440

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“…Room temperature data suggest that calcareous deposits are usually formed on steel under cathodic protection, being composed of a thin Mg-rich layer on the steel surface with a Ca-rich layer on top of the Mg-rich layer [16][17][18][19]. Somehow, the conditions of this experiment did not allow the Ca-rich layer to form.…”

Section: Discussionmentioning

confidence: 78%

“…This, however, is only true for lower temperatures, as higher temperatures tend to shift (lower) the neutral point of water as well as the minimum pH required for the precipitation of brucite (Tables 4 and 5). The reason for the increase in the surface pH that results in the precipitation of calcareous matter has been studied before [16][17][18][19][20]. The anode (aluminum, in the case of TSA-coated steel) polarizes the steel, resulting in the production of hydroxyl ions (OH − ), which increases the interfacial pH.…”

Section: Discussionmentioning

confidence: 99%

Thermally Sprayed Aluminum Coatings for the Protection of Subsea Risers and Pipelines Carrying Hot Fluids

Cé

Paul

2016

Coatings

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This paper reports the effect of boiling synthetic seawater on the performance of damaged Thermally Sprayed Aluminum (TSA) on carbon steel. Small defects (4% of the sample's geometric surface area) were drilled, exposing the steel, and the performance of the coating was analyzed for corrosion potential for different exposure times (2 h, 335 h, and 5000 h). The samples were monitored using linear polarization resistance (LPR) in order to obtain their corrosion rate. Scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) were used for post-test characterization. The results showed that a protective layer of Mg(OH) 2 formed in the damaged area, which protected the underlying steel. Additionally, no coating detachment from the steel near the defect region was observed. The corrosion rate was found to be 0.010-0.015 mm/year after 5000 h in boiling synthetic seawater.

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Role of sulphate ions on the formation of calcareous deposits on steel in artificial seawater; the formation of Green Rust compounds during cathodic protection

Cited by 62 publications

References 34 publications

Natural Deposit Coatings on Steel during Cathodic Protection and Hydrogen Ingress

Natural Deposit Coatings on Steel during Cathodic Protection and Hydrogen Ingress

A Study of Calcareous Deposits on Cathodically Protected Mild Steel in Artificial Seawater

Thermally Sprayed Aluminum Coatings for the Protection of Subsea Risers and Pipelines Carrying Hot Fluids

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