What is Fusion Bonded Epoxy (FBE) Coating? Technical Explanation

Fusion bonded epoxy (FBE) coating is a type of protective coating used to prevent corrosion and provide a durable, protective layer on metal surfaces, particularly steel pipes and fittings. It is applied as a dry powder to the heated surface of the metal, where it melts and fuses to form a continuous, adherent, and chemically cross-linked epoxy layer. This process creates a tough, corrosion-resistant barrier that effectively shields the metal substrate from environmental factors and corrosive substances.

The corrosion of pipelines used in the oil and gas industry poses a substantial threat to their longevity and environmental safety. This issue becomes even more critical when dealing with the extraction of oil from ultra-deep seawater fields due to the extreme operating conditions. Therefore, the development of effective protective coatings for steel pipelines is paramount to safeguard against highly corrosive environments.

In this study, the researchers explored the application of fusion bonded epoxy (FBE) coatings on carbon steel surfaces that had been chemically modified with organosilanes. The objective was to assess the potential of these coatings in providing protection against corrosion and deterioration in harsh marine settings.

The chosen material for the study was carbon-steel API 5L X42, a grade defined by the American Petroleum Institute. Initially, this steel was chemically treated with two distinct organosilanes: 3-APTES (3-Aminopropyltriethoxysilane) and 3-GPTMS (3-Glycidyloxypropyltrimethoxysilane). Following the surface modification, FBE composite coatings were applied.

Extensive characterizations of the systems were performed, encompassing each constituent and the interface between the steel and the coating. Contact angle measurements and Fourier transform infrared spectroscopy (FTIR) revealed that the chemical treatment with amine and glycidyl silanes effectively altered the steel surface. This modification resulted in the formation of covalent bonds at the interface, enhancing the hydrophobicity compared to untreated steel surfaces.

Further analyses, including scanning electron microscopy, atomic force microscopy, X-ray diffraction, and FTIR, unveiled that the FBE coatings consisted of an epoxy-based organic matrix derived from bisphenol-A diglycidyl ether (DGEBA). These coatings were fortified with uniformly distributed inorganic phases comprising calcium silicates and TiO2 particles.

Additionally, the chemical functionalization of steel surfaces using amino and glycidyl silanes had a notable impact on the interfacial properties between the steel and FBE coatings. This alteration led to increased adhesion strength, especially in the case of 3-APTES-modified steel when compared to 3-GPTMS-modified steel. However, both cases predominantly exhibited cohesive rupture within the FBE component.

In summary, in this article, we investigated the potential of FBE coatings applied to chemically modified steel surfaces for corrosion protection in harsh marine environments. The study demonstrated the effectiveness of this approach in enhancing hydrophobicity and adhesion strength, which are crucial factors in mitigating corrosion and ensuring the longevity of pipelines in challenging operational conditions.

Manufacturing Process of FBE powder

The manufacturing process of FBE (Fusion Bonded Epoxy) powder coatings involves several essential components within a powder coating manufacturing plant:

1. Weighing Station: This station is responsible for accurately measuring and weighing the various components that make up the FBE formulation.
2. Pre-blending Station: The weighed components are pre-blended in high-speed mixers. This mixing stage ensures that the ingredients are thoroughly combined before further processing.
3. Extruder: The mix is then transferred to a high-shear extruder. FBE extruders typically employ a single or dual screw configuration enclosed in a fixed clamshell barrel. The extruder operates within a temperature range of approximately 50°C to 100°C. Within the extruder, the FBE blend is compressed, heated, and melted into a semi-liquid state. This process ensures the thorough dispersion of the mix’s ingredients. Importantly, due to the extruder’s rapid operation and the relatively low temperature in the barrel, the epoxy and hardener components do not undergo significant chemical reactions.
4. Solidification and Sizing: The semi-liquid extrudate is passed between cold rollers, causing it to solidify into a brittle sheet. Subsequently, it moves to a “Kibbler” machine, which chops the sheet into smaller chips.
5. Grinding and Sizing: These chips are further processed through high-speed grinders, often referred to as classifiers. The goal is to reduce the particle size to less than 150 micrometers. Standard specifications require that 100% of the particles pass through 250-micrometer sieves, with a maximum of 3% retained on 150-micrometer sieves.
6. Packaging: The final FBE powder coating product is carefully packaged in sealed containers. Special attention is given to preventing moisture contamination during this stage.
7. Storage: FBE powder coatings are typically stored in air-conditioned warehouses with controlled temperatures below 25°C (77°F).

In summary, the manufacturing process of FBE powder coatings involves precise weighing, pre-blending, extrusion, solidification, sizing, grinding, and careful packaging to produce a high-quality powder coating product. Proper storage conditions are maintained to preserve the product’s integrity and performance.

Application Process of FBE Coating

The application process for Fusion Bonded Epoxy (FBE) coatings consists of three essential stages, regardless of the type or shape of the steel surface to be coated:

1. Surface Cleaning:

• The steel surface is thoroughly cleaned to remove rust, scale, and contaminants such as grease or oil.
• Common methods include blast cleaning, solvent cleaning, and burn-off.

2. Heating and FBE Powder Application:

• The cleaned metal part is heated to the recommended application temperature for FBE powder coatings. Typical temperatures range from 225°C to 245°C.
• Heating methods include induction heating, oven heating, and infrared heating.
• FBE powder is placed on a fluidization bed, where it behaves like a fluid when suspended in a stream of air.
• The fluidized powder is sprayed onto the hot substrate using suitable spray guns.
• Electrostatic spray guns may be used to give the powder particles a positive electric charge, ensuring uniform coverage.
• For internal surfaces of pipes, spraying lances are used, traveling from end to end while the pipe rotates.
• Standard coating thickness ranges from 250 to 500 micrometers, although variations are possible based on service conditions.
• The molten powder bonds with the steel, solidifies into a coating, and undergoes curing under the hot conditions.
• Complete curing can occur within seconds to minutes, depending on the FBE coating system.

3. Advantages of FBE Application:

• FBE application offers several advantages over conventional liquid coating methods:
  • Ease of application
  • Minimal material waste
  • Rapid application process
  • Faster production rates due to shorter cure schedules

The application method varies based on the shape of the steel surface, with continuous linear application for pipes and rebar, manual spray guns for fittings, and a “fluid-dip” process for heated components. Proper surface preparation and heating are critical to achieving a high-quality FBE coating.

FAQs: