Partial repair of thermally sprayed and sealed corrosion protection – Organic coating material or thermal spraying?

Bridges are subject to extreme corrosion attack due to the surrounding conditions. Chlorides in a maritime atmosphere, de-icing salts or Sulphur Dioxide in an industrial atmosphere cause high corrosion rates if mild steel is left unprotected. The paper shows the best corrosion protection for a long service life under all these conditions offered by a duplex-coating combining a thermally sprayed zinc-based layer with a fitting top-coat. It introduces the thermal spraying process and ist application on bridges, which can be performed in the plant or at the worksite, du r ing erection and for repair work. Thermal Spraying is a well-established process which has been in existence for more than a hundred years. It is used manually, semi-automated and fully automated. Thermal Spraying with zinc and zinc-alloys is a "cold" process having no influence on the microstructure of the coated steel. It refers to worldwide standards and norms, which assure the highest quality of material, work and coatings. Worldwide references on steel bridges are presented as well as the latest developments in research. Throughout this abstract, the results of an intensive study over a service life of more than 26 years of duplex systems for Offshore Wind Energy plants is shown. In conclusion, the presentation also offers a quick view to the application of thermal spraying on concrete bridge structures to protect the rebar by cathodic protection.

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Influence of substrate temperature on adhesion of thermally sprayed Ni-5%Al coatings

Journal of Achievements of Materials and Manufacturing Engineering ◽

10.5604/01.3001.0010.5138 ◽

2017 ◽

Vol 1 (83) ◽

pp. 33-40

Author(s):

D. Ostrowski ◽

R. Starosta

Keyword(s):

Adhesion Strength ◽

Steel Substrate ◽

Thermal Spraying ◽

Coating Material ◽

Flame Spraying ◽

Al Alloy ◽

Thermally Sprayed Coatings ◽

Machine Parts ◽

Thermally Sprayed ◽

Sprayed Coatings

Purpose: In the paper effect of pre-heating the steel substrate on the adhesion of thermally sprayed Ni-5%Al alloy coatings was presented. The reason for the topic was the discrepancy between the literature data on the effect of the preheating of the substrate on the adhesion of the coatings and the guidelines of the coating material manufacturer. Design/methodology/approach: As a coating material the ProXon 21021 was used. It is an alloy of nickel aluminium and molybdenum. This material is often used during the regeneration of machine parts in the shipbuilding industry. The coatings by flame spraying using the Casto-Dyn DS 8000 torch were obtained. The samples were made of steel C45. The specimens to which the coating was applied were characterized by a similar surface roughness. Before applying the coatings, the samples were preheated to a temperature of 50 to 400°C. The coatings tested were similar in thickness. Adhesion strength of the coatings was determined by the pull-off method. Findings: The quantitative comparative assessment of the adhesion strength of thermally sprayed coatings can be implemented by a pull-off. The highest value of adhesion strength for coatings applied on substrates of 50, 300 and 400°C was found. Considering that the technical thermally sprayed coatings of Ni-5% Al, often require an additional machining, they must be applied to the steel substrate surface at 50°C. Research limitations/implications: The adhesion test of the coatings has not been executed in accordance with the requirements of PN-EN 582 Thermal spraying - Determination of tensile adhesive strength. Therefore, the quantitative results obtained are only comparative. Practical implications: The results obtained show that the regeneration coatings of ProXon 201021 material should only be applied to pre-heated by flame (among other things, to degrease the surface of the substrate) to a temperature of approximately 50°C. At the time the coatings are characterized by the greatest adhesion to the steel substrate. Originality/value: The study demonstrated the usefulness of cheaper method of pull-offs to evaluate the adhesion of flame sprayed coatings. The results show that there is no need for a pre-heating of the substrate between 150 and 250°C before thermal spraying. This article may be useful for technologists designing the process of regeneration of machine parts using flame spraying.

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EIS study of the corrosion behavior of an organic coating applied on Algerian oil tanker

Metallurgical Research & Technology ◽

10.1051/metal/2020064 ◽

2020 ◽

Vol 117 (6) ◽

pp. 610

Author(s):

Nadia Hammouda ◽

Kamel Belmokre

Keyword(s):

Corrosion Protection ◽

Electrochemical Impedance ◽

Paint Film ◽

Organic Coating ◽

Diffusion Resistance ◽

Double Layer Capacitance ◽

Carbon Steel Surface ◽

Chloride Environment ◽

Oil Tanker ◽

Epoxy Paint

Organic coatings are widely employed in the corrosion protection of most metal surfaces, particularly steel. They provide a barrier against corrosive species present in the environment, due to their high resistance to oxygen, water and ions transport. This study focuses on the evaluation of corrosion protection performance of epoxy paint on the carbon steel surface in chloride environment (3% NaCl) by Electrochemical Impedance Spectroscopy (EIS). The electrochemical behavior of painted surface was estimated by EIS parameters that contained paint film resistance, paint film capacitance and double layer capacitance. On the basis of calculation using EIS spectrums it was observed that pore resistance (Rpore) decreased with the appearance of doubled layer capacitance (Cdl) due to the electrolyte penetration through the film. This was further confirmed by the decrease of diffusion resistance (Rd) which was also the indicator of the deterioration of paint film protectiveness. Microscopic analyses have shown that oxidation dominates the corroded surfaces.

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