Liquid Epoxy Coatings vs Fusion Bonded Epoxy Coatings

Protecting pipelines and infrastructure from corrosion is a critical challenge in oil and gas, water, and mining industries. Two widely used coating technologies—liquid Epoxy (LE) coatings and Fusion Bonded Epoxy (FBE) coatings—offer robust protection, but each has distinct advantages and considerations. Liquid Epoxy Coatings vs Fusion Bonded Epoxy Coatings: which should you choose? Understanding their differences can help engineering operators and coating designers make informed decisions regarding cost, performance, and application suitability.

Coating Technologies: Liquid Epoxy Coatings vs Fusion Bonded Epoxy Coatings

Fusion Bonded Epoxy (FBE) Coatings

FBE coatings are thermoset polymer coatings that provide excellent adhesion and corrosion protection for pipelines and metal surfaces. The application process involves:

• Preheating the substrate to a high temperature (typically 180–250°C).
• Applying the powdered epoxy, which melts and forms a uniform protective layer.
• Curing to create a rigid, durable finish.

FBE coatings are known for:

• Superior adhesion to steel, offering long-term corrosion resistance.
• High resistance to soil stress and mechanical damage, making them ideal for buried or submerged pipelines.
• For enhanced protection, there are Single-layer or multi-layer applications, with additional coatings like polyethylene (3LPE) or polypropylene (3LPP).

Liquid Epoxy (LE) Coatings

LE coatings are two-component systems that cure at ambient temperatures. The application process includes:

• Surface preparation to ensure strong adhesion.
• Mixing and applying the epoxy using spray, brush, or roller methods.
• Allowing time for curing, which can vary based on environmental conditions.

LE coatings are valued for:

• Ease of application in the field without requiring high temperatures.
• Excellent adhesion in both dry and wet conditions.
• Versatility, as they can be applied to irregular surfaces and complex geometries.
• Lower initial equipment costs since they do not require preheating and specialized application facilities.

Performance: Liquid Epoxy Coatings vs Fusion Bonded Epoxy Coatings

Parameter	Liquid Epoxy Coatings (LE)	Fusion Bonded Epoxy Coatings (FBE)
Application Method	Applied on-site using brush, roller, or spray. Requires proper surface preparation (abrasive blasting) and precise application to ensure uniform thickness.	Applied in a controlled factory environment using electrostatic spraying. The powder is melted and cured on the preheated substrate, forming a seamless and durable coating.
Curing Time	Slow curing process; typically takes several hours to days, depending on ambient temperature and humidity. Can be accelerated with heat but remains slower than FBE.	Due to heat-induced polymerization, the coating cures rapidly within minutes. It is fully hardened before the pipe leaves the coating facility.
Field Applicability	Well-suited for field application, repair work, and coating complex structures or irregular surfaces.	Primarily used for factory-applied coatings. Difficult to repair in the field due to the high-temperature curing requirement.
Mechanical Properties	It offers good adhesion and corrosion resistance but has lower hardness and wear resistance than FBE. It is also more susceptible to mechanical damage.	It provides excellent hardness, abrasion resistance, impact strength, and flexibility. It also withstands mechanical stress, reducing the risk of coating failure.
Adhesion Strength	Strong adhesion to steel surfaces but may degrade over time, especially in harsh environments or under mechanical stress.	Exceptional adhesion to steel due to chemical bonding during curing, ensuring long-term durability and resistance to delamination.
Toxicity	May contain volatile organic compounds (VOCs) and hazardous solvents. Proper ventilation and safety measures are required during application.	Non-toxic once cured, but application involves high-temperature processing, requiring controlled handling.
Service Life	Typically 10–30 years, depending on exposure conditions and maintenance. Susceptible to degradation under UV and mechanical wear.	Long-term protection of 30+ years in well-applied conditions, with minimal degradation over time. Requires less maintenance compared to LEC.
Applicable Fluids	Suitable for transporting oil, gas, and water. Provides effective corrosion protection in buried and subsea environments.	Highly resistant to a wide range of aggressive media, including H₂S, CO₂, O₂, acids, alkalis, salts, hydrocarbons, and organic substances. Also resistant to microbiologically influenced corrosion (MIC) in soil and seawater.
Corrosion Resistance	Provides good protection against corrosion but is vulnerable to mechanical damage and requires periodic maintenance.	Excellent resistance to chemical corrosion, including acidic and saline environments. Works synergistically with cathodic protection systems to enhance durability.
Operating Temperature	Suitable for temperatures ranging from -20°C to 80°C. Performance may decline at high temperatures.	Superior thermal stability with a wide operating range from -30°C to 100°C. High glass transition temperature (Tg) ensures structural integrity under high temperatures.
Cost	Lower initial cost, but higher long-term maintenance costs due to potential degradation and recoating requirements.	Higher initial cost due to specialized equipment and factory-controlled processing, but lower long-term costs due to durability and minimal maintenance.

Coating Standards: Liquid Epoxy Coatings vs Fusion Bonded Epoxy Coatings

Both FBE and LE coatings must meet stringent industry standards to ensure performance and longevity. Key standards include:

• DEP 31.40.30.32-Gen./ISO 21809-2: Petroleum and natural gas industries — External coatings for buried or submerged pipelines used in pipeline transportation systems — Part 2: Single layer fusion-bonded epoxy coatings
• NACE SP0394: Guidelines for liquid epoxy coatings.
• AWWA C210: Liquid-Epoxy Coatings and Linings for Steel Water Pipe and Fittings
• AWWA C213: Fusion-Bonded Epoxy Coating for the Interior and Exterior of Steel Water Pipelines
• CSA Z245.20: External fusion bond epoxy coating for steel pipe
• COM-SU-4042-I: Single and Dual Layer Fusion-Bonded Epoxy Systems for External Pipeline Coatings

Ensuring compliance with these standards is crucial for maintaining pipeline integrity and regulatory approval.

Testing and Inspection Standards: Liquid Epoxy Coatings vs Fusion Bonded Epoxy Coatings

Testing and inspection standards for Liquid Epoxy Coatings (LEC) and Fusion Bonded Epoxy Coatings (FBE) are critical to ensure their performance, durability, and suitability for specific applications, particularly in industries like oil and gas, water pipelines, and infrastructure protection. Below are some of the key standards and tests commonly used for LEC and FBE coatings:

1. General Standards for Epoxy Coatings

• ISO 21809-2: Petroleum and natural gas industries – External coatings for buried or submerged pipelines used in pipeline transportation systems – Part 2: Fusion-bonded epoxy coatings.
• ISO 12944: Paints and varnishes – Corrosion protection of steel structures by protective paint systems.
• NACE SP0188: Discontinuity (Holiday) Testing of Protective Coatings.
• ASTM D7234: Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.

2. Specific Tests for Fusion Bonded Epoxy (FBE) Coatings

FBE coatings are widely used for pipeline protection. Key tests include:

Adhesion Testing

• ASTM D6677: Standard Test Method for Evaluating Adhesion by Knife.
• ASTM D4541: Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers.

Cathodic Disbondment

• ASTM G8: Standard Test Methods for Cathodic Disbonding of Pipeline Coatings.
• ASTM G95: Standard Test Method for Cathodic Disbondment Test of Pipeline Coatings (Attached Cell Method).

Impact Resistance

• ASTM G14: Standard Test Method for Impact Resistance of Pipeline Coatings (Falling Weight Test).

Flexibility

• ASTM D522: Standard Test Methods for Mandrel Bend Test of Attached Organic Coatings.

Holiday Detection

• NACE SP0188: Holiday detection to identify coating discontinuities.
• ASTM G62: Standard Test Methods for Holiday Detection in Pipeline Coatings.

Abrasion Resistance

• ASTM D4060: Standard Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser.

Thickness Measurement

• ASTM D7091: Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals.

3. Specific Tests for Liquid Epoxy Coatings (LE)

LE is often used for tank linings, structural steel, and concrete protection. Key tests include:

Adhesion Testing

• ASTM D4541: Pull-off adhesion testing.
• ASTM D3359: Standard Test Methods for Measuring Adhesion by Tape Test.

Chemical Resistance

• ASTM D1308: Standard Test Method for Effect of Household Chemicals on Clear and Pigmented Organic Finishes.
• ASTM D543: Standard Practices for Evaluating the Resistance of Plastics to Chemical Reagents.

Abrasion Resistance

• ASTM D4060: Taber Abraser test.

Holiday Detection

• ASTM G62: Holiday detection for thin-film coatings.

Thickness Measurement

• ASTM D4138: Standard Test Methods for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive Means.
• ASTM D7091: Non-destructive thickness measurement.

Cure Testing

• ASTM D4752: Standard Test Method for Measuring MEK Resistance of Ethyl Silicate (Inorganic) Zinc-Rich Primers.

Water Immersion and Humidity Resistance

• ASTM D870: Standard Practice for Testing Water Resistance of Coatings Using Water Immersion.
• ASTM D2247: Standard Practice for Testing Water Resistance of Coatings in 100% Relative Humidity.

4. Inspection Procedures

• Visual Inspection: Check for uniformity, color, and surface defects.
• Holiday Detection: Use low- or high-voltage holiday detectors to identify coating flaws.
• Dry Film Thickness (DFT): Measure using magnetic or ultrasonic gauges.
• Adhesion Testing: Perform pull-off or knife adhesion tests.
• Cure Testing: Verify proper curing using solvent rub tests (e.g., MEK resistance).

5. Industry-Specific Standards

• API RP 5L2: Recommended Practice for Internal Coating of Line Pipe for Non-Corrosive Gas Transmission Service.
• AWWA C210: Standard for Liquid-Epoxy Coating Systems for the Interior and Exterior of Steel Water Pipelines.
• NACE RP0394: Application, Performance, and Quality Control of Plant-Applied, Fusion-Bonded Epoxy External Pipe Coating.

6. Quality Control

• Ensure proper surface preparation (e.g., SSPC-SP10/NACE No. 2 for near-white metal blast cleaning).
• Monitor environmental conditions (temperature, humidity) during application.
• Conduct regular inspections during and after application.

Liquid Epoxy Coatings vs Fusion Bonded Epoxy Coatings: How to Choose?

When selecting a coating system, consider the following factors:

• Environmental Conditions: Harsh conditions, such as high temperatures and aggressive soils, favor FBE coatings, while LE coatings perform well in diverse field environments.
• Project Scope and Location: FBE coatings provide a durable, factory-applied solution for new pipeline construction. For rehabilitation and maintenance, LE coatings offer flexibility and ease of application.
• Budget Constraints: If upfront cost is a concern, LE coatings may be preferable. However, for long-term asset protection, FBE coatings may provide better value.

Conclusion

Both Liquid Epoxy Coatings (LE) and Fusion Bonded Epoxy Coatings (FBE) serve critical roles in protecting pipelines and infrastructure from corrosion. FBE coatings offer unmatched durability and mechanical resistance, making them ideal for new pipeline installations. LE coatings provide flexible, cost-effective solutions for field applications and maintenance. By understanding the strengths and limitations of each system, engineers and designers can make informed choices to optimize performance, cost-effectiveness, and long-term asset protection. If you need steel pipes with these two coatings, please feel free to reach out to us at [email protected].