Glass-Fused-to-Steel (GFS) and Fusion-Bonded Epoxy (FBE) Coated Steel are two popular corrosion-resistant coatings used in various industries to protect steel structures from corrosion and harsh environments. While both coatings offer excellent corrosion protection, they have distinct characteristics and applications. In this comparison, we will explore the differences between Glass-Fused-to-Steel and Fusion-Bonded Epoxy Coated Steel:
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1. Coating Composition:
Glass-Fused-to-Steel (GFS): GFS is a unique combination of two materials - glass and steel. The steel substrate is coated with a layer of enamel (glass) on both sides, and then the enamel is fused to the steel substrate through a high-temperature firing process. This fusion creates a highly durable and chemically resistant bond between the glass and steel.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE is a two-part epoxy coating applied to the steel substrate through a fusion bonding process. The epoxy resin and curing agent are mixed and then applied to the heated steel surface, where they chemically react and bond to form a protective coating.
2. Corrosion Resistance:
Glass-Fused-to-Steel (GFS): GFS provides exceptional corrosion resistance due to the impermeable glass layer, which acts as a barrier against corrosive elements. The glass enamel resists chemical attack and protects the steel substrate from corrosion caused by moisture, chemicals, and other environmental factors.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE also offers excellent corrosion protection. The epoxy coating forms a strong and durable barrier that prevents corrosive substances from reaching the steel substrate. FBE is particularly effective in protecting against soil, water, and chemical corrosion.
3. Adhesion to Steel Substrate:
Glass-Fused-to-Steel (GFS): GFS provides superior adhesion to the steel substrate because the enamel is fused with the steel during the firing process. This fusion creates a molecular bond, ensuring long-term adhesion and preventing delamination.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings have excellent adhesion to the steel substrate when applied correctly. The fusion bonding process ensures strong adhesion and prevents the coating from peeling or flaking off the steel surface.
4. Temperature Resistance:
Glass-Fused-to-Steel (GFS): GFS has excellent temperature resistance, making it suitable for a wide range of applications, including both high-temperature and low-temperature environments. The glass enamel can withstand temperatures ranging from -40°C to 500°C (-40°F to 932°F) without degradation.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings are limited in their temperature resistance compared to GFS. They are generally suitable for applications with operating temperatures up to 150°C (302°F). Beyond this range, the epoxy may begin to degrade and lose its protective properties.
5. Impact Resistance:
Glass-Fused-to-Steel (GFS): GFS offers excellent impact resistance due to the tough and durable nature of the glass enamel. It can withstand mechanical impacts and resist damage caused by external forces, making it ideal for applications in harsh industrial environments.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings provide good impact resistance but may be less durable than GFS when subjected to severe impacts or mechanical stress.
6. Abrasion Resistance:
Glass-Fused-to-Steel (GFS): GFS coatings are highly abrasion-resistant, making them suitable for applications where the coated surface may come into contact with abrasive materials or conditions.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings also offer some degree of abrasion resistance, but they may not be as resilient as GFS in abrasive environments.
7. Flexibility and Coating Thickness:
Glass-Fused-to-Steel (GFS): GFS coatings are rigid and inflexible due to the nature of the glass enamel. The coating thickness is typically uniform across the entire surface.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings can be applied with varying thicknesses, and the flexibility of the epoxy allows for some degree of conformability to irregular surfaces.
8. Installation and Maintenance:
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Glass-Fused-to-Steel (GFS): GFS coatings are factory-applied and require precision manufacturing and firing processes. Installation on-site involves bolting together the pre-fabricated steel panels. Maintenance is minimal and typically involves periodic inspections and cleaning.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings are applied on-site using specialized equipment. Surface preparation and application must be carefully executed to ensure proper adhesion. Maintenance may involve periodic inspections, touch-ups, or recoating in areas with damage or wear.
9. Applications:
Glass-Fused-to-Steel (GFS): GFS is widely used in applications requiring long-term durability, such as water and wastewater storage tanks, biogas reactors, anaerobic digesters, and industrial storage tanks.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings are commonly used in pipeline systems for oil, gas, and water transportation, as well as in underground structures, such as pipelines and storage tanks.
10. Cost Considerations:
Glass-Fused-to-Steel (GFS): GFS coatings are considered a premium option and may have a higher upfront cost due to the precision manufacturing and firing process. However, their long-term durability and minimal maintenance requirements can result in cost savings over the life of the structure.
Fusion-Bonded Epoxy (FBE) Coated Steel: FBE coatings are generally more cost-effective than GFS, making them a popular choice for pipelines and underground structures. However, they may require more frequent maintenance and recoating over time.
Conclusion
In summary, both Glass-Fused-to-Steel (GFS) and Fusion-Bonded Epoxy (FBE) Coated Steel offer excellent corrosion protection for steel structures. GFS provides superior adhesion, temperature resistance, and impact resistance, making it suitable for a wide range of applications, including water storage, wastewater treatment, and industrial tanks. On the other hand, FBE coatings offer good adhesion, cost-effectiveness, and flexibility, making them suitable for pipeline systems and underground structures. The choice between GFS and FBE depends on the specific application, operating conditions, and budget considerations. Properly applied and maintained, both coatings can extend the life of steel structures and protect them from the damaging effects of corrosion.
Fusion bonded epoxy (FBE) coatings have been a widely used method of corrosion prevention for pipeline fittings in oil and gas, chemical processing, and other harsh environment industries since their introduction in the s. Although a popular choice, it is not without its limitations.
Newer technologies and materials certainly have been developed over the last twenty years that offer a compelling improvement to the FBE materials of the past. This paper describes how rotolining, a rotational molding process, provides a more durable, longer-life solution for pipelines and is proven effective in hundreds of the most demanding applications around the world.
Rotolining essentially molds a permanently bonded liner to the inside diameter of a pipe or to the working surfaces inside of a pipe fitting. Its chemical and mechanical properties provide a variety of performance enhancements that cannot be matched by fusion bonded epoxy coatings.
To fully understand the differences between FBE and rotolining, we need to first take a look at how fusion bonded epoxy coatings are applied.
Whenever a surface coating is applied, the finished quality of the coating generally depends upon the thoroughness of the surface preparation. This is true when painting a car, staining a piece of furniture, or applying a corrosion protection liner. For both FBE and roto-lining, the surface first needs to be coated to be cleaned of any grease or oil and then taken to a condition called &#;near white metal&#; by shot or sandblasting. The abrasive process creates an additional surface area on a microscopic level and leaves the surface chemically active. Both of which improve bonding.
If the working surface is not completely clean of contamination prior to application, the coating will fail prematurely, due to lack of adherence. Poor bonding can lead to voids between the liner and the surface, eventually causing delamination of the liner from the surface to which it was applied. The process of applying fusion bonded epoxy is very similar to powder coating. An epoxy resin powder that has been positively charged is applied to a negatively charged and heated part to be coated. The electrostatic attraction between the two holds the epoxy powder in place until it liquefies and flows uniformly over the hot surface. The coated part is then cooled at a controlled rate to promote uniformity in the coated surface. When properly prepared and fully cured, FBE linings provide a seamless, permanently bonded method of corrosion prevention.
That sounds good in theory, but it&#;s not always the case in practice. There are some inherent limitations of FBE liners that negatively impact their durability. Due to constraints in the application process, coating thicknesses with FBE are limited to 0.04&#;, roughly the thickness of a credit card. While this will provide some degree of corrosion prevention when used as a liner in a pipe fitting, its durability is compromised by its minimal thickness. FBE is typically applied with a spray nozzle or gun, with long, straight lengths of pipes being coated relatively easily with automated equipment. However, the complex geometries that can be present in pipe fittings are a different ball game. Typically, these parts have to be coated manually, if they can be coated at all, which can lead to inconsistencies in the coating that then lead to liner failure.
Solid particles in flow media, such as sand, will wear out FBE liners rapidly. This limitation is exacerbated in sections of the piping system that are not straight lines and constant cross-sectional area, such as an elbow, tee, or throat. These geometries cause turbulence in the flow media, which accelerates wear on these internal surfaces.
Rotolining is a highly effective alternative to FBE, providing the same or better protection without FBE&#;s limitations.
Rotolining of course shares the same surface preparation requirements as fusion bonded epoxy. All working surfaces are cleaned of grease and oil and then abraded to near white metal. A polymer chosen for the appropriate corrosion protection qualities is applied in the granular form inside the fitting or pipe section. It is then and heated while being simultaneously rotated about two perpendicular axes. During the heating cycle, the polymer particles melt and adhere to the metal substrate, forming a uniform layer of thermoplastic. Typical wall thickness extends up to 0.450&#;, depending on the size of the part and service requirements. Some of the most common liner materials are HDPE (high-density polyethylene), ETFE (Tefzel), PFA (Teflon), PVDF (Kynar), and Nylon 12.
After being fully coated the fitting is then cooled by a combination of forced air and water mist. The resin solidifies and permanently bonds to the substrate with a bond strength exceeding the tensile strength of the liner, creating a seamless fully protected component. The liner material extends out onto the flange face and is machined to tight tolerances to provide a sealing surface. This added benefit of rotolining may eliminate the need for gaskets between fittings. The entire process of lining a part can usually be completed in less than a day, depending on the complexity of the geometry and the amount of surface preparation that needs to be done.
There are some size restraints on parts that can be roto-lined, as the parts need to be able to fit into the oven used in the lining process. However, straight lengths of pipe up to 20 feet long and fittings or other parts such as storage vessels that will fit within a 12-foot sphere are possible.
The ability to coat parts with complex geometrics, to a much greater thickness, while using a wider variety of coating materials, gives roto-lining a distinct advantage over fusion-bonded epoxy. FBE and roto-lining are both capable of providing a seamless protective coating, roto-lining lasts longer over a much broader range of operating environments.
Why does durability really matter? Because the longer a process fitting can stay functional without concern of corrosion, the longer the process can run without downtime. Beyond the cost of lost production associated with downtime, there is the cost to replace the affected fitting, which might be 20 feet underground. Decommissioning of a line and excavation are costly undertakings. It is obvious that the run-time between maintenance shutdowns should be extended as long as possible.
Of course, the cost differences between these two coating methods do need to be considered as well. Roto-lining can cost up to twice as much as FBE for a given part. However, a roto-lined coating can be expected to last three times longer FBE, in the same operating environment. So, while initial purchase price alone favors FBE, roto-lining is the clear winner for lifetime cost.
There are additional &#;soft cost&#; issues worth noting. Because of their limited durability, FBE-coated fittings require more frequent inspection and maintenance. Additionally, the potential safety and environmental risks associated with a liner failure are minimized by using roto-lined parts.
Rotolining technology is newer than FBE; and, as a result, not familiar to some engineers. However, its use is growing as it becomes better known in the industry. With the wide range of available lining materials and thicknesses, more than ten times those of FBE coatings, the corrosion protection lining performance of rotolined coatings makes it a compelling choice &#; especially for the most demanding applications.
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