Galvanizing vs. Powder Coating: A Comparative Analysis
June 17, 2024Custom coater's have the unique challenge of determining customer specific coatings systems on an almost daily basis. While a majority of the jobs have a high requirement for aesthetic over function – if you ever encounter a job that is going to be used in a harsh environment such as a chemical processing plant or providing an effective corrosion resistant barrier, then you should familiarize yourself with fusion bonded epoxy (FBE) coatings. They can also be an effective solution in converting liquid coating systems to powder coating.
The aim of this article is to give you a crash course in what separates an FBE from your typical epoxy primers, where and when it should be used, and when it should not.
History of FBE Coatings
The journey of Fusion Bonded Epoxy (FBE) coatings began in the early 1960s, marking a significant advancement in the field of protective coatings. Initially developed for use on external pipe joints, FBE coatings quickly demonstrated their robustness and effectiveness in providing corrosion resistance. Their early adoption was driven by the need for reliable coatings in the oil and gas industry, where infrastructure durability is paramount.
By the late 1960s and early 1970s, the application of FBE coatings expanded beyond pipe joints to include entire pipelines, driven by their exceptional adhesion properties and mechanical strength.
Over the decades, technological advancements have refined the formulation and application techniques of FBE coatings, further enhancing their protective capabilities. Today, FBE coatings are extensively utilized in various industries, including construction and transportation, solidifying their role as indispensable tools for ensuring long-term durability and performance in harsh environments.
A different kind of Epoxy
While the resin system is epoxy based, FBE differs from commonly available epoxy coatings in that it is highly chemical resistant, the particle size is significantly larger to allow for higher film build (typical target film build is 3.5mils / 87microns, whereas FBE film build is up to 24 mils/600microns), and that many FBE formulations can cure within seconds at > 425ºF.
The preferred method for preparing a surface to receive an FBE coating is abrasive blasting. Unlike standard epoxies that are commonly used in decorative applications and will work well over a chemical pretreatment, FBE is designed to be applied heavy and therefore needs a mechanical anchor to provide additional bond. A blast profile between 2.5 – 4.5 mils will provide a sufficient anchor pattern, and the steel should be cleaned to at least SSPC-SP10 Near White / NACE No. 2. In the case of a project that has a specification provided to the custom coater, this should be followed in place of manufacturers recommendations.
Application methods
There are three different methods of application for FBE:
- Fluidized bed dip: A large tank with a fluidizing membrane deposits powder onto a preheated part – likely not a method employed by many custom coaters.
- Preheating: Preheat part up to >425ºF and then flock the coating on the part. This will result in a completed coating within a matter of minutes and likely not require a final cure in your oven.
- Two coats of FBE: This ethod is to ensure the part is properly grounded, apply a base layer of FBE, wet it out in your oven (being sure not to allow the part temperature to climb over 300ºF, otherwise you risk curing your base coat before applying the top coat), and applying a second layer to the desired coating thickness.
Why is it so great?
By their very nature, epoxies provide excellent adhesion through polar and mechanical bonds. A polar bond occurs at the molecular level when the resin molecules are attracted to the substrate molecules. Combined with a properly prepared substrate resulting in a strong mechanical bond, and you will have an incredibly strong bond.
In photo below, a sample plate of mild steel was simply solvent wiped and then coated with a popular FBE. When a pull off adhesion test was done, the result was surprising. The FBE actually bonded to the mill scale on the test plate to the point where at approximately 1400 PSI, the testing device removed the FBE with the mill scale attached from the base steel. Even without the recommended mechanical preparation the coating proved to have incredible bonding strength.
The other great benefit of this coating is the fact that it is a thermoset powder coating. When the cure cycle is initiated by elevated temperature, a chemical reaction is set off that result in the durability and chemical resistance afforded by FBE.
Furthermore the goods can typically be turned around quicker than most conventional liquid systems will allow as the cure time is much lower.
A word of caution
While FBE has a wide range of applications, it also has a wide range of formulations. An example of a potential issue is found when evaluating pipe lining for potable water. NSF 61 or AWWA-C213 is a designation that some – not all – FBE coatings have. Likewise the chemical resistance of an NSF 61 certified coating may not be suitable for use in a mining application, for instance.
The other thing to remember is that as an epoxy coating, it is susceptible to chalking from UV exposure. If UV stability is required, there is the option of applying a UV stable top coat over the FBE Primer. However, again depending on the application, you may have to mask to prevent that top coat from getting on critical areas i.e. the inside of a potable water pipe lining as seen in the photo below.
Moving forward
FBE could present you with opportunities to expand your offerings. Speak with your coating provider about what projects you may have coming up which are currently specify a liquid coating system – if your supplier is able to provide you with an equivalent or better system using FBE, and the engineer who originally authored the specification can have it approved, it will be a win-win!
It is important to choose a coater that has the appropriate processes in place and uses quality monitoring equipment (a DFT gauge is a must!).
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