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How to Choose Appropriate Anti-Corrosion Coil Components

20 May.,2024

How to Choose Appropriate Anti-Corrosion Coil Components

This article has been updated. It is accurate as of 9/23/20.

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For commercial operations that rely on effective heat transfer, external corrosion of heat exchanger components is a major concern. When left unchecked, corrosion can significantly reduce a coil's effectiveness, but sometimes it’s difficult to know which anti-corrosion option best meets your needs.

Fortunately, manufacturers offer a variety of corrosion-resistant products, including pre-coated finstock, full-coil coatings, spray-on topcoats, and baked-on epoxies. This post will focus on advantages and tradeoffs of all four options, while outlining some suitable applications for each.

Option #1: Electrofin E-coat

Also known as electrocoating or cathodic deposition, such as Electrofin (a PPG product), e-coating is one of the most effective means of corrosion protection available. The ElectroFin coating process involves electrically charging an assembled coil, then submerging it into an oppositely charged bath of water and paint solids. The coil essentially becomes a magnet to which the paint is attracted (think powder-coating, but underwater).

The coil is then rinsed and oven-baked, resulting in a very even hydrophobic coat with uniform dry film thickness of anywhere from 0.6 to 1.2 mil. This includes fin edges, meaning the coil is fully encapsulated and protected. When properly maintained, E-coat can provide effective corrosion protection for years.

Advantages: E-coat is an effective means of protecting a coil’s joints from galvanic corrosion, which occurs when dissimilar metals interact over time in the presence of an electrolyte. The difference in the electrode potential of the two metals results in one acting as a cathode, and the other serving as an anode, which makes for an accelerated corrosion of the anode metal. This corrosion weakens the connection at the coil’s joints, reducing its effectiveness. E-coat provides insulation between the two metals, effectively creating a barrier that hinders the occurrence of the galvanic action.

E-coating also leaves the coil resistant to corrosion caused by other sources, even relatively strong acids and bases.

Tradeoffs: E-coating a coil is more expensive than using pre-coated finstock, and its hydrophobic nature makes it unsuitable for applications where the presence of beaded water could have negative effects (like in an evaporator). E-coating also requires the coil to be shipped to a coater, coated, then shipped back, which adds lead time.

Applications: E-coat provides robust defense against corrosion, withstanding 6,000+ hours during ASTM B117 tests. This resilience makes it well-suited for HVAC use in coastal areas. It’s also frequently used in heat exchangers on ships and other marine environments for the same reasons. See the chart below for e-coat’s performance on other tests.

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Option #2: Alucoat Waterfin 700

Waterfin 700 is a hydrophilic pre-coated finstock product manufactured for use in the production of heat exchangers. It’s coated in a silica-free lacquer and is available in several thicknesses, alloys, and tempers.

Advantages: Like E-coat, Waterfin 700 protects against galvanic corrosion, too. However, it does so by eliminating contact between dissimilar metals. By using collars that flare out, the coil’s tubes never come in contact with any uncoated fin material, preventing a dielectric circuit and impeding the galvanic reaction. Waterfin 700’s film also covers the area of the fin away from the joint, providing moderate corrosion protection across the remainder of the fin.

Price point is another primary benefit of pre-coat, as it’s cheaper than e-coat. Also, unlike electrocoating, Waterfin 700 is ready to use right away. It’s sold in reels like non-coated finstock, so there’s no need to send anything to a coater, which saves lead time.

Tradeoffs: Waterfin 700 provides a lower level of corrosion defense than E-coat, withstanding 1000 hours in ASTM B117 tests, and is appropriate for heat exchangers in less extreme corrosive environments.

Applications: The hydrophilic nature of Alucoat’s Waterfin 700 makes it suitable for environments like evaporators, where water needs to flow, rather than bead. Waterfin 700 would be a good choice for use in heat exchangers in food processing or residential and commercial HVAC applications. Waterfin 700 also provides corrosion protection from chemicals and pollutants, and would hold up well in environments where either are present.

Option #3: E-coat + spray-on hydrophil topcoat

A third option involves applying a hydrophilic spray-on coating product after the coil has been E-coated. Upon curing, the hydrophilic coating develops an ultrathin hydrophilic surface where water is attracted to the surface of the substrate, resulting in condensate draining off the bottom of the coil rather than blowing off the coil face.

Advantages: Not only does the coil benefit from the corrosion resistance and overall strength of the E-coat, the addition of the hydrophilic layer allows the coil to be used in applications that require water to flow rather than bead. This coating provides marked improvement in evaporator condensate removal without carryover, while also increasing air velocity up to 26% compared to an uncoated fin. The hydrophil topcoat also provides its own moderate abrasion resistance without loss of hydrophilicity.

Tradeoffs: Aside from a minor added cost (1.5 – 2%), the tradeoffs of adding a hydrophilic topcoat are minimal. The topcoat is applied at the same facility where the coil is E-coated, so there’s no additional lead time or added freight cost.

Option #4: Heresite P-413 Baked Phenolic Epoxy

A fourth corrosion-resistant option is a baked-on phenolic coating manufactured by Heresite and designed specifically for use on heat exchanger external surfaces. It can be applied via full immersion, flood, or spray methods.

Advantages: Due to its dense cross linking, Heresite P-413 can provide high levels of corrosion resistance even when applied as thin film. Heresite also holds an ANSI 51 certification for non-contact food zones, while also providing resistance to a multitude of chemicals.

Tradeoffs: The added step can contribute to increased lead time (around 10 days compared to e-coat’s 7, but Heresite does offer expedited options). As far as thickness goes, Heresite and E-coat are fairly similar, with each having a dry film thickness of roughly 1 mil.

Applications: Heresite P-413 is designed for use on components and parts in air conditioning and refrigeration system, especially those that operate in moderate to severely corrosive environments, such as marine and offshore applications, among others.

Article 34:10 most frequently asked questions about GI coils

Here are the 10 most frequently asked questions about GI coils:

1. What Is A GI Coil?

A GI (Galvanized Iron) Coil Is A Type Of Steel Coil That Has Been Coated With A Layer Of Zinc Through A Process Called Galvanization. This Coating Helps To Protect The Underlying Steel From Corrosion, Making The GI Coil More Durable And Long-Lasting Compared To Untreated Steel Coils. GI Coils Are Commonly Used In A Variety Of Applications Including Construction, Automotive Manufacturing, Appliances, And General Engineering. They Are Known For Their Strength, Corrosion Resistance, And Affordability, Making Them A Popular Choice In Many Industries.

2. What Are The Advantages Of Using GI Coils?

Galvanized iron (GI) coils offer 8 advantages, making them popular in various industries:

1. Corrosion Resistance

2. Longevity

3. Strength and Toughness

4. Versatility

5. Cost-Effectiveness

6. Aesthetic Appeal

7. Recyclability

8. Protection for Base Metal

Overall, the advantages of using GI coils make them a preferred choice for a wide range of applications, including construction, automotive manufacturing, appliances, agricultural equipment, and more.

3. How Are GI Coils Manufactured?

GI (Galvanized Iron) coils are manufactured through a process called hot-dip galvanizing. Here's 7 general of the process:

1. Preparation Of Steel:

2. Pickling

3. Luxing

4. Galvanizing

5. Cooling

6. Finishing

7. Inspection

The resulting GI coils are highly corrosion-resistant and are commonly used in a wide range of applications, including construction, automotive, and manufacturing industries.

4. What Industries Typically Use GI Coils?

Galvanized Iron (GI) coils find applications across various industries due to their corrosion resistance and durability. Some of the industries that typically use GI coils include:

1. Construction

2. Automotive

3. Appliances

4. Industrial Equipment:

5. Electrical

6. Transportation

7. Infrastructure

5. What Are The Different Grades Of GI Coils Available?

Galvanized Iron (GI) coils are available in different grades, which are typically categorized based on the thickness of the zinc coating applied to the steel substrate. The most common grades of GI coils include:

1. SGCC (DX51D):

This is one of the most widely used grades of GI coils. SGCC stands for "Hot-Dip Galvanized Steel Sheet and Coil", and DX51D is the European equivalent. These coils have a standard zinc coating thickness and are suitable for general applications in various industries.

2. SGCD (DX52D)

SGCD or DX52D grade GI coils have a higher zinc coating thickness compared to SGCC/DX51D coils. They offer improved corrosion resistance and are often used in environments with higher levels of moisture or exposure to corrosive elements.

3. SGCE (DX53D)

SGCE or DX53D grade GI coils have an even higher zinc coating thickness than SGCD/DX52D coils. These coils provide enhanced corrosion protection and are suitable for applications where extended durability is required, such as in coastal areas or harsh industrial environments.

4. SGCF (DX54D):

SGCF or DX54D grade GI coils have the highest zinc coating thickness among the commonly available grades. These coils offer superior corrosion resistance and are suitable for demanding applications where maximum protection against corrosion is essential, such as in marine environments or chemical processing plants.

It's important to note that the specific grades and designations may vary slightly depending on regional standards and specifications. Additionally, there may be other specialized grades of GI coils available for specific applications or industries, but the ones mentioned above are the most commonly used grades in general industrial and commercial applications.

6. What Are The Standard Sizes And Dimensions Of GI Coils?

The standard sizes and dimensions of Galvanized Iron (GI) coils can vary depending on the manufacturer, region, and specific requirements of the customer. However, there are some common size ranges that are widely available:

1. Width:

GI coils typically come in widths ranging from 600mm to 1500mm (approximately 24 inches to 59 inches). The choice of width depends on factors such as the intended application, machinery constraints, and transportation considerations.

2. Thickness:

The thickness of GI coils can vary from as thin as 0.12mm to as thick as 4.0mm (approximately 0.0047 inches to 0.157 inches). The specific thickness required depends on the strength and durability requirements of the application.

3. Coil Weight:

The weight of GI coils can range from a few hundred kilograms to several metric tons, depending on the width, thickness, and length of the coil. Common coil weights range from 3 to 15 metric tons (approximately 6600 to 33000 pounds).

4. Inner Diameter:

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The inner diameter of GI coils typically ranges from 508mm to 610mm (approximately 20 inches to 24 inches). This inner diameter is standardized to fit various types of coil handling and processing equipment.

5. Outer Diameter:

The outer diameter of GI coils can vary depending on factors such as coil width, thickness, and weight. However, common outer diameters range from 1000mm to 2000mm (approximately 39 inches to 79 inches).

6. Length:

GI coils are usually supplied in continuous lengths, with typical coil lengths ranging from 1000mm to 3000mm (approximately 39 inches to 118 inches). However, longer or custom lengths may be available upon request.

It's important to note that these dimensions are general guidelines, and actual sizes may vary depending on the specific specifications provided by the customer or the manufacturing capabilities of the supplier. Additionally, GI coils can be cut to custom lengths or slit to narrower widths to meet the requirements of different applications.

7. How Do GI Coils Compare To Other Types Of Steel Coils?

GI (Galvanized Iron) Coils Are A Specific Type Of Steel Coil That Has Undergone A Galvanization Process To Prevent Corrosion. Here's How They Compare To Other Types Of Steel Coils:

1. Corrosion Resistance:

GI coils have superior corrosion resistance compared to other types of steel coils. This is because they are coated with a layer of zinc, which acts as a sacrificial anode, protecting the underlying steel from rust and corrosion. This makes GI coils ideal for outdoor or humid environments where corrosion is a concern.

2. Durability:

The galvanization process adds an extra layer of protection to GI coils, making them more durable compared to other types of steel coils. They are less likely to rust or corrode over time, resulting in a longer lifespan.

3. Cost-Effectiveness:

While GI coils may be slightly more expensive upfront due to the galvanization process, they are generally more cost-effective in the long run because of their extended lifespan and reduced maintenance requirements. They may require less frequent replacement or repair compared to other types of steel coils.

4. Strength:

GI coils typically have similar strength characteristics to other types of steel coils of comparable thickness. The galvanization process does not significantly alter the mechanical properties of the steel, so GI coils retain their strength and structural integrity.

5. Appearance:

GI coils have a characteristic shiny, metallic appearance due to the zinc coating. This can be desirable for certain applications where aesthetics are important. However, for applications where appearance is not a concern, other types of steel coils may be preferred.

Overall, GI coils offer excellent corrosion resistance, durability, and cost-effectiveness compared to other types of steel coils, making them a popular choice for a wide range of applications, including roofing, automotive, construction, and manufacturing.

8. What Is The Process For Galvanizing GI Coils?

The process of galvanizing GI coils involves several steps:

1. Surface Preparation:

The steel coils are cleaned to remove any surface contaminants such as oil, grease, or dirt. This is typically done using a chemical cleaning process or by immersing the coils in a degreasing solution.

2. Pickling:

The coils are then immersed in a pickling solution, usually an acidic bath such as hydrochloric acid or sulfuric acid. This removes any remaining oxides and mill scale from the surface of the steel, preparing it for the galvanizing process.

3. Fluxing:

After Pickling, The Coils Are Rinsed To Remove Any Residual Pickling Solution And Then Immersed In A Flux Solution. The Flux Helps To Prevent Oxidation Of The Steel Surface Before It Is Galvanized And Promotes The Adhesion Of The Zinc Coating.

4. Galvanizing:

The prepared steel coils are passed through a bath of molten zinc at temperatures typically around 450°C (850°F). The coils are carefully submerged in the zinc bath, ensuring that the entire surface is coated with a layer of molten zinc. This process is known as hot-dip galvanizing.

5. Quenching:

Once the steel coils have been galvanized, they are removed from the zinc bath and allowed to cool in the open air or by quenching in water. This solidifies the zinc coating and ensures that it adheres firmly to the surface of the steel.

6. Finishing:

After cooling, the galvanized GI coils may undergo further processing such as skin-pass rolling or tension leveling to improve surface finish and flatness. They may also be cut to size and coil-wound for shipment to customers.

The galvanizing process creates a durable, corrosion-resistant coating of zinc on the surface of the steel coils, providing long-lasting protection against rust and corrosion in a variety of environments.

9. How Long Do GI Coils Typically Last?

The lifespan of GI (Galvanized Iron) coils can vary depending on factors such as the thickness of the zinc coating, the environmental conditions they are exposed to, and the quality of the galvanizing process. However, in general, GI coils are known for their durability and long lifespan.

Under normal conditions, where they are not subjected to extreme corrosion or mechanical damage, GI coils can last for several decades. It's not uncommon for properly galvanized GI coils to remain corrosion-free and structurally sound for 20 to 50 years or even longer.

Factors that can affect the lifespan of GI coils include exposure to corrosive environments such as coastal areas with high salt content in the air, industrial environments with chemical pollutants, or frequent exposure to moisture and harsh weather conditions.

Regular maintenance, such as periodic inspections for damage or signs of corrosion, can help extend the lifespan of GI coils. Additionally, applying protective coatings or sealants as needed can provide extra protection against corrosion and prolong the lifespan of the coils.

Overall, GI coils are valued for their longevity and resistance to corrosion, making them a popular choice for a wide range of applications where durability and reliability are important.

10. What Factors Affect The Price Of GI Coils?

Several factors can influence the price of GI (Galvanized Iron) coils:

1. Raw Material Costs:

The price of GI coils is heavily influenced by the cost of raw materials, primarily steel and zinc. Fluctuations in the prices of these materials due to factors such as supply and demand, tariffs, and currency exchange rates can impact the overall cost of GI coils.

2. Galvanizing Process:

The process of galvanizing involves several steps, including surface preparation, pickling, fluxing, and hot-dip galvanizing. The cost of these processes, including labor, energy, and overheads, can affect the price of GI coils.

3. Zinc Coating Thickness:

The thickness of the zinc coating applied to GI coils can vary depending on the desired level of corrosion resistance and durability. Thicker coatings require more zinc and may result in higher production costs, which can influence the price of GI coils.

4. Market Demand:

Like any commodity, the price of GI coils is influenced by supply and demand dynamics in the market. Increased demand for GI coils, particularly during periods of high construction activity or infrastructure development, can drive prices higher.

5. Quality And Standards:

GI coils manufactured to higher quality standards or certifications may command a premium price due to their superior performance and reliability. Customers may be willing to pay more for GI coils that meet specific industry standards or regulatory requirements.

6. Transportation And Logistics:

The cost of transporting GI coils from the manufacturing facility to the customer's location can impact the overall price. Factors such as distance, mode of transportation, and fuel prices can influence transportation costs and, consequently, the final price of GI coils.

7. Economic And Political Factors:

Economic conditions, trade policies, and geopolitical events can also affect the price of GI coils. Trade tariffs, sanctions, or changes in government regulations can lead to fluctuations in prices or supply chain disruptions.

Overall, the price of GI coils is influenced by a combination of factors related to raw materials, manufacturing processes, market dynamics, quality standards, and external economic and political factors. Understanding these factors can help manufacturers, suppliers, and customers make informed decisions regarding the purchase and sale of GI coils.

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