Fusion bonded epoxy coating

Last updated

Fusion bonded epoxy coating, also known as fusion-bond epoxy powder coating and commonly referred to as FBE coating, is an epoxy-based powder coating that is widely used to protect steel pipe used in pipeline construction from corrosion. It is also commonly used to protect reinforcing bars (though being phased out as of 2005 [1] ) and on a wide variety of piping connections, valves etc. [2] FBE coatings are thermoset polymer coatings. [3] They come under the category of protective coatings in paints and coating nomenclature. The name fusion-bond epoxy is due to resigning cross-link and the application method, which is different from a conventional paint. In 2020 the market size was quoted at 12 billion dollars. [4]

Contents

The resin and hardener components in the dry powder FBE stock remain unreacted at normal storage conditions. At typical coating application temperatures, usually in the range of 180 to 250 °C (356 to 482 °F), the contents of the powder melt and transform to a liquid form. The liquid FBE film wets and flows onto the steel surface on which it is applied, and soon becomes a solid coating by chemical cross-linking, assisted by heat. This process is known as “fusion bonding”. The chemical cross-linking reaction taking place in this case is irreversible. Once the curing takes place, the coating cannot be returned to its original form by any means. Application of further heating will not “melt” the coating and thus it is known as a “thermoset” coating.

History

Since their introduction as a protective coating in early 1960s, FBE coating formulations had gone through vast improvements and developments. Today, various types of FBE coatings, which are tailor-made to meet various requirements are available. FBEs are available as stand-alone coatings as well as a part in multi-layers. FBE coatings with different properties are available to suit coating application on the main body of pipe, internal surfaces, girth welds as well as on fittings.

Chemistry of FBE coatings

Structure of unmodified Bis phenol A type epoxy prepolymer. n denotes the number of polymerized sub units and is in the range from 0 to about 25 Epoxy prepolymer chemical structure.png
Structure of unmodified Bis phenol A type epoxy prepolymer. n denotes the number of polymerized sub units and is in the range from 0 to about 25

Essential components of a powder coating are: [5]

  1. Resin.
  2. Hardener or curing agent.
  3. Fillers and extenders.
  4. Colour pigments.

The resin and hardener part together is known as the "Binder". As the name indicates, in Fusion bonded epoxy coatings the resin part is an "epoxy" type resin. “Epoxy” or “Oxirane” structure contains a three membered cyclic ring — one oxygen atom connected to two carbon atoms – in the resin molecule. This part is the most reactive group in the epoxy resins. Most commonly used FBE resins are derivatives of bisphenol A and epichlorohydrin. However, other types of resins (for example bisphenol F type) are also commonly used in FBE formulations to achieve various properties, combinations or additions. Resins are also available in various molecular lengths, to provide unique properties to the final coating.

The second most important part of FBE coatings is the curing agent or hardener. Curing agents react either with the epoxy ring or with the hydroxyl groups, along the epoxy molecular chain. Various types of curing agents, used in FBE manufacture, include dicyandiamide, aromatic amines, aliphatic diamines and organic acid anhydrides. [6] The selected curing agent determines the nature of the final FBE product – its cross linking density, chemical resistance, brittleness, flexibility etc. The ratio of epoxy resins and curing agents in a formulation is determined by their relative equivalent weights.

In addition to these two major components, FBE coatings include fillers, pigments, extenders and various additives, to provide desired properties. These components control characteristics such as permeability, hardness, colour, thickness, gouge resistance etc. All of these components are normally dry solids, even though small quantities of liquid additives may be used in some FBE formulations. If used, these liquid components are sprayed into the formulation mix during pre-blending in the manufacturing process.

The standard for FBE coating of pipelines is ISO 21809 Part 2.

FBE powder manufacturing process

Essential parts of a powder coating manufacturing plant are:

  1. weighting station,
  2. pre-blending station,
  3. an extruder, and
  4. a classifier or grinding unit.

The components of the FBE formulation are weighed and pre-blended in high speed mixers. The mix is then transferred to a high-shear extruder. FBE extruders incorporate a single or dual screw setup, rotating within a fixed clamshell barrel. A temperature range[ vague ] from 50 °C to 100 °C is used within the extruder barrel. This setup compresses the FBE blend, while heating and melting it to a semi-liquid form. During this process, the ingredients of the molten mix are dispersed thoroughly. Because of the fast operation of the extruder and relatively low temperature within the barrel, the epoxy and hardener components will not undergo a significant chemical reaction. The molten extrudate then passes between cold-rollers and becomes a solid, brittle sheet. It then moves to a “Kibbler”, which chops it into smaller chips. These chips are ground, using high speed grinders (classifiers) to a particle size of less than 150 micrometers (standard specifications requires 100% pass through in 250 micrometer sieves and maximum 3% retains in 150 micrometer sieve). The final product is packaged in closed containers, with particular care given to avoid moisture contamination. Normal storage temperatures of FBE powder coatings are below 25 °C (77 °F) in air-conditioned warehouses.

FBE coating application process

Regardless of the shape and type of steel surface to be coated, the FBE powder coating application has three essential stages:

  1. the steel surface is thoroughly cleaned,
  2. the cleaned metal part is heated to the recommended FBE powder application temperature, and
  3. the application and curing stage.

The advantage of pipe and rebar is that their round shape allows continuous linear application over the exterior surface, while the parts are moved in a conveyor through the powder application booth, ensuring high throughput. On fittings, etc., the coating is applied by manual spray guns. Another method of application is "fluid-dip" process, in which the heated components are dipped in a fluidized powder bed (see below).

Surface preparation—blast cleaning

Blast cleaning is the most commonly used method for preparation of steel surfaces. [7] This effectively removes rust, scale, slats, etc., from the surface and produces an industrial grade cleaning and a rough surface finish. The roughness of the steel achieved after blasting is referred to as profile, which is measured in micrometers or mils. Commonly used to profile ranges for FBE coatings are 37 to 100 micrometers (1.5 to 4 mils). Profile increases the effective surface area of the steel. The cleanliness achieved is assessed to ISO 8501-1 grades: these originated from a set of photographic slides in a Swedish standard (SIS) showing exemplars of the common terminology of white-metal, near white-metal, etc. Typically, SA 2½ is used for pipelines (equivalent to NACE N°2).

It is important to remove grease or oil contamination prior to blast cleaning. Solvent cleaning, burn-off, etc., are commonly used for this purpose. In the blast cleaning process, compressed air (90 to 110 psi/610 to 760 kPa) is used to force an abrasive onto the surface to be cleaned. Aluminum oxide, steel grit, steel shot, garnet, coal slag, etc., are the frequently used abrasives. Another method of blast cleaning is centrifugal blast cleaning, which is especially used in cleaning the exterior of pipe. In this method, abrasive is thrown to the rotating pipe body, using a specially designed wheel, which is rotated at high speed, while the abrasive is fed from the centre of the wheel.

Heating and FBE powder application

Heating can be achieved by using several methods, but the most commonly used ones are ‘’induction heating’’ or ‘’oven heating’’. The steel part is passed through a high frequency alternating current magnetic field, which heats the metal part to the required FBE coating application temperature. Typical application temperature for a stand alone FBE is 225° to 245°C. When used as a primer in a multi-layer polyolifine system, application temperature may be dropped based on FBE manufacturer's recommendations, in order to meet the "inter-coat adhesion" parameters. Special grade FBE coatings which can be applied at temperatures as low as 175 °C has been developed recently by certain FBE powder manufacturers. Other methods of heating are ‘’oven heating’’, ‘’infra-red heating’’, etc. The FBE powder is placed on a “fluidization bed”. In a fluidization bed, the powder particles are suspended in a stream of air, in which the powder will “behave” like a fluid. Once the air supply is turned off, the powder will remain in its original form. The fluidized powder is sprayed onto the hot substrate using suitable spray guns. An electrostatic spray gun incorporates an ionizer electrode on it, which gives the powder particles a positive electric charge. The steel to be coated is “grounded” through the conveyor. The charged powder particles uniformly wraps around the substrate, and melts into a liquid form. Internal surfaces of pipes are coated using spraying lances, which travel from one end to the other end of the heated pipe at a uniform speed, while the pipe is being rotated in its longitudinal axis.

Standard coating thickness range of stand-alone FBE coatings is between 250 and 500 micrometers, even though lower or higher thickness ranges might be specified, depending on service conditions. The molten powder ‘flows’ into the profile and bonds with the steel. The molten powder will become a solid coating, when the ‘gel time’ is over, which usually occurs within few seconds after coating application. The resin part of coating will undergo cross-linking, which is known as “curing” under the hot condition. Complete curing is achieved either by the residual heat on the steel, or by the help of additional heating sources. Depending on the FBE coating system, full cure can be achieved in less than one minute to few minutes in case of long cure FBE's, which are used for internal pipe coating applications.

Rebars are coated in a similar manner as coating application, on the exterior of pipes. For FBE coating application on the interior of pipe surface, a lance is used. The lance enters into the pre-heated pipe, and starts spraying the powder from the opposite end, while the pipe is being rotated on its axis and the lance pulls out in a pre-determined speed.

On fittings such as Tee's, elbows, bends, etc., powder can be sprayed using hand held spray guns. Small sized fittings can also be coated by dipping in a fluidized bed of powder, after heating the steel to the required powder application temperature. After field welding of the pipe ends, FBE can be applied on the weld area as well.

Advantages of FBE application over conventional liquid coating application are:

  • Ease of application,
  • Less waste of material,
  • Rapid application,
  • Cure schedules, which means faster production rates

Failures

There are a number of potential failure modes for Fusion bonded epoxy. One of these failure modes is by ultraviolet degradation. [8]

Manufacturers

The world's leading FBE manufacturers are Sherwin-Williams (Valspar), SolEpoxy (former Henkel/Dexter), KCC Corporation, Jotun Powder Coatings, 3M, Axalta Coating Systems, Akzo Nobel, BASF, and Rohm & Haas. [9]

See also

Related Research Articles

<span class="mw-page-title-main">Paint</span> Pigment applied over a surface that dries as a solid film

Paint is a material or mixture that, when applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image or images known as a painting. Paint can be made in many colors and types. Most paints are either oil-based or water-based, and each has distinct characteristics.

Fiberglass or fibreglass is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth. The plastic matrix may be a thermoset polymer matrix—most often based on thermosetting polymers such as epoxy, polyester resin, or vinyl ester resin—or a thermoplastic.

<span class="mw-page-title-main">Epoxy</span> Type of material

Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also collectively called epoxy. The IUPAC name for an epoxide group is an oxirane.

<span class="mw-page-title-main">Varnish</span> Transparent hard protective finish or film

Varnish is a clear transparent hard protective coating or film. It is not to be confused with wood stain. It usually has a yellowish shade due to the manufacturing process and materials used, but it may also be pigmented as desired. It is sold commercially in various shades.

<span class="mw-page-title-main">Thermosetting polymer</span> Polymer obtained by irreversibly hardening (curing) a resin

In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst. Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.

<span class="mw-page-title-main">Extrusion</span> Process of pushing material through a die to create long symmetrical-shaped objects

Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex cross-sections; and to work materials that are brittle, because the material encounters only compressive and shear stresses. It also creates excellent surface finish and gives considerable freedom of form in the design process.

<span class="mw-page-title-main">Coating</span> Substance spread over a surface

A coating is a covering that is applied to the surface of an object, or substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. powder coatings.

<span class="mw-page-title-main">Powder coating</span> Type of coating applied as a free-flowing, dry powder

Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint, which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a thick, tough finish that is more durable than conventional paint. Powder coating is mainly used for coating of metal objects, particularly those subject to rough use. Advancements in powder coating technology like UV-curable powder coatings allow for other materials such as plastics, composites, carbon fiber, and MDF to be powder coated, as little heat or oven dwell time is required to process them.

Conformal coating is a protective, breathable coating of thin polymeric film applied to printed circuit boards (PCBs). Conformal coatings are typically applied at 25–250 μm thick to the electronic circuitry to protect against moisture and other potentially damaging conditions.

Electronic packaging is the design and production of enclosures for electronic devices ranging from individual semiconductor devices up to complete systems such as a mainframe computer. Packaging of an electronic system must consider protection from mechanical damage, cooling, radio frequency noise emission and electrostatic discharge. Product safety standards may dictate particular features of a consumer product, for example, external case temperature or grounding of exposed metal parts. Prototypes and industrial equipment made in small quantities may use standardized commercially available enclosures such as card cages or prefabricated boxes. Mass-market consumer devices may have highly specialized packaging to increase consumer appeal. Electronic packaging is a major discipline within the field of mechanical engineering.

<span class="mw-page-title-main">Thermal spraying</span> Coating process for applying heated materials to a surface

Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.

<span class="mw-page-title-main">Heat-shrinkable sleeve</span>

Heat-shrinkable sleeve is a corrosion protective coating for pipelines in the form of a wraparound or tubular sleeve that is field-applied.

Redux is the generic name of a family of phenol–formaldehyde/polyvinyl–formal adhesives developed by Aero Research Limited (ARL) at Duxford, UK, in the 1940s, subsequently produced by Ciba (ARL). The brand name is now also used for a range of epoxy and bismaleimide adhesives manufactured by Hexcel. The name is a contraction of REsearch at DUXford.

Substrate is a term used in materials science and engineering to describe the base material on which processing is conducted. Surfaces have different uses, including producing new film or layers of material and being a base to which another substance is bonded.

<span class="mw-page-title-main">Automotive paint</span> Coloring and resistance to corrosion of cars

Automotive paint is paint used on automobiles for both protective and decorative purposes. Water-based acrylic polyurethane enamel paint is currently the most widely used paint for reasons including reducing paint's environmental impact.

<span class="mw-page-title-main">Epoxy granite</span> Mixture of epoxy and granite

Epoxy granite, also known as synthetic granite, is a polymer matrix composite and is a mixture of epoxy and granite commonly used as an alternative material for machine tool bases. Epoxy granite is used instead of cast iron and steel for improved vibration damping, longer tool life, and lower assembly cost, and thus better properties for stabilizing and housing machines.

A thermoset polymer matrix is a synthetic polymer reinforcement where polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements. They were first developed for structural applications, such as glass-reinforced plastic radar domes on aircraft and graphite-epoxy payload bay doors on the Space Shuttle.

According to EN 13523-0, a prepainted metal is a ‘metal on which a coating material has been applied by coil coating’. When applied onto the metallic substrate, the coating material forms a film possessing protective, decorative and/or other specific properties.

HDPE pipe is a type of flexible plastic pipe used to transfer fluids and gases. It is often employed for replacing aging concrete or steel main pipelines. Constructed from the thermoplastic HDPE, it has low permeability and robust molecular bonding, making it suitable for high-pressure pipelines. HDPE pipe is often used for water mains, gas mains, sewer mains, slurry transfer lines, rural irrigation, fire-suppression system supply lines, electrical and communication conduits, and stormwater and drainage pipes.

References

  1. ↑ Rostam, Steen (2005). Design and Construction of Segmental Concrete Bridges for Service Life of 100 to 150 Years. American Segmental Bridge Institut. pp. 19–20. Archived from the original on 2022-04-07. Retrieved 2021-06-08.
  2. ↑ "Fusion Bonded Epoxy (FBE) | Pipeline Induction Heat". www.pipelineinductionheat.com. Retrieved 2021-11-17.
  3. ↑ "Fusion-Bonded Epoxy Coating Protects Water Pipeline from Corrosion". www.materialsperformance.com. Retrieved 2021-11-17.
  4. ↑ "New Advances in Powder Coating Technology". American Coatings Association. Retrieved 2021-11-17.
  5. ↑ "Comparing Powder and Liquid Coatings for Pipeline Applications". www.pcimag.com. Retrieved 2021-11-17.
  6. ↑ "Toward High Glass-Transition Temperatures in Epoxy Powder Coatings Based on BTDA®". American Coatings Association. Retrieved 2023-07-24.
  7. ↑ "The Science Behind Field-Applied Liquid Epoxy Pipeline Coatings". www.materialsperformance.com. Retrieved 2021-11-17.
  8. ↑ "Failure of FBE Coatings in Gas Transporting Pipelines". nace.mydigitalpublication.com. Retrieved 2021-11-17.
  9. ↑ "Fusion Bonded Epoxy Coatings companies". Xpert Environmental. November 2021.

Further reading


This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.