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ABSTRACT In the present work a new approach based on an electrochemical scanning cell was investigated, allowing fast, quasinondestructive, and quantitative measurements on thermalsprayed, metallic coatings. A wide range of microstructures was produced by atmospheric and vacuum plasma spraying and flame spraying of nickel-based powders (Ni, NiCr, NiCrAlY) on mild steel substrates. Measurements on thermalsprayed nickel-based coatings performed by the scanning technique yielded good agreement and predictability of the results gained by the salt spray (fog) test on the same set of samples. A lateral resolution in the range of the coating thickness turned out to be appropriate to investigate the significant defect structures of the entire range of microstructures. A quantitative characterization was possible within a few tens of minutes, allowing for the fast comparison of different systems, regardless of their surface topography and geometry. A comparison of the electrochemical measurement to the 700-h salt spray test showed an agreement of the two techniques. The investigation showed the influence of the spraying technique and the composition of the powder. A small scanning area of 18 mm by 18 mm seems to be statistically representative for thermally sprayed nickel coatings in terms of predictability of performance during salt spray testing. In the salt spray tests high-density vacuum plasma-sprayed NiCrAlY coatings with lower anodic current peaks were superior to coatings with high local current densities such as flamesprayed Ni. Thermal spraying is an effective way of improving the surface properties of components in numerous industrial applications. Thermal-sprayed coatings are widely used as protective coatings in corrosion prevention, e.g., as Al or Al-Zn alloys in steel construction (oil platforms, bridges)1 or Ni-based or ceramic coatings.2 Standards such as ISO 147133 and ISO 20634 are related to the corrosion protection by thermal spraying of zinc and aluminum, and their alloys. Kawakita, et al.,5 reported that in the case of high-velocity oxy-fuel (HVOF)-sprayed nickel-based alloy coatings, the corrosion resistance against seawater was improved with lower oxide content and reduced porosity. However, the characterization of the prepared layers still represents a technological challenge and is not available on-site in field applications so far. A major problem in characterizing thermal-sprayed coatings is revealing local defects, such as irregularities in pore size, cracks, or delamination. These problems are overcome by a recently developed scanning electrochemical technique.6-7 It allows for quantitative characterization of the coating properties within a few tens of minutes for an area of 100 mm2 or approximately 1 s per data point. In the present work, the results obtained with the new technique are compared to the salt spray fog test. The performance of the parts in corrosion protection was often characterized by the salt spray (fog)
- Europe (1.00)
- Asia (1.00)
- North America > United States (0.93)
- South America (0.68)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals (0.68)
- Materials > Metals & Mining (0.66)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT In general, reinforced concrete has proved to be successful in terms of structural performance and durability. However, there are instances of premature failure of reinforced concrete components caused by corrosion of the reinforcement. Two factors provoking depassivation of the steel are the ingress of chloride ions from deicing salts or seawater or the reaction of the alkaline pore solution with carbon dioxide (CO2) from the atmosphere, or carbonation. Corrosion then will start in the presence of moisture and oxygen. On new structures, the most effective measure to improve durability can be achieved in the design stage using adequate concrete cover and high-quality concrete. This will prevent aggressive substances (e.g., chloride ions) such as deicing salts or seawater from reaching the rebar within the design life. Additional protective measures can be applied (e.g., adding inhibitors) in sufficiently high concentrations to the mixing water. In an earlier paper, the authors studied the effect of adding a hydroxyalkylamine-based inhibitor on preventing the onset of corrosion.1 An inhibitor concentration of 10% could prevent corrosion initiation completely in a saturated (sat.) calcium hydroxide (Ca[OH]2) solution with 1 M sodium chloride (NaCl). However, it was found that the inhibiting properties could be lost by evaporation of the volatile constituent of the inhibitor. On existing structures, the deterioration process can reach different stages according to age, exposure condition, concrete cover, and quality of the struc-
- Europe > United Kingdom > England (0.29)
- Europe > Switzerland (0.29)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.48)
- Water & Waste Management > Water Management > Water & Sanitation Products (0.42)
- Materials > Chemicals > Specialty Chemicals (0.42)
- (2 more...)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
ABSTRACT The damage caused by corrosion to rebars in reinforced concrete structures results in significant costs. Corrosion attacks can be caused by chloride ions from deicing salts penetrating to the steel, which result in pitting corrosion of the passive steel or by reaction of the alkaline pore solution with carbon dioxide (CO2), which results in a pH drop and the depassivation of the steel. Despite the huge demand, a simple, cheap, and reliable technique that either protects the steel from corrosion or at least lowers its corrosion rate is still lacking. Besides coating the rebar and the hydrophobic treatment of the concrete surface, the use of corrosion inhibitors is of increasing interest. By definition, inhibitors are substances that hinder the corrosion process and therefore result in a decrease of the dissolution rate of the steel. The application of corrosion inhibitors in reinforced concrete is possible by the addition to mixing water or by application on the surface of the concrete structure. Addition to the mixing water does not require any additional working steps and allows a simple handling of the inhibitor, unless it affects the properties of the cement paste adversely. Application from the concrete surface could be a promising technique to protect already existing structures or increase the lifetime of structures that already show corrosion attack. The application of the inhibitor on the concrete surface requires the diffusion of the substance to the rebar where it has to reach a sufficiently high concentration to protect steel against
- North America > United States (0.46)
- Europe > Switzerland (0.28)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)