What Is Epoxy Coating?

Quick Answer

Epoxy coating is a thermosetting polymer applied to steel pipe surfaces for corrosion protection. The three main types—Fusion Bonded Epoxy (FBE), liquid epoxy, and coal tar epoxy—vary in application method, thickness, and temperature resistance. FBE is the most widely used epoxy coating in the oil and gas pipeline industry, applied to both external and internal pipe surfaces.

Epoxy Coating Types

Epoxy coatings form a cross-linked molecular structure when cured, creating a hard, chemical-resistant barrier that bonds tightly to the steel substrate. Unlike thermoplastic coatings, cured epoxy cannot be re-melted.

Each type has a specific application niche:

• FBE (Fusion Bonded Epoxy): Powder-applied at 230-245°C onto preheated pipe. The epoxy melts, flows, gels, and cures in a continuous process. Single-layer FBE (300-600 microns) is the standard standalone external/internal coating for moderate-temperature pipelines.
• Liquid Epoxy: Two-component (resin + hardener) system applied by brush, roller, or spray at ambient temperature. Used for field repairs, joint coating, and tank linings. Cure time ranges from hours to days depending on formulation and temperature.
• Coal Tar Epoxy (CTE): Epoxy modified with coal tar pitch for enhanced water resistance. Applied as a thick-film liquid coating (400-1000 microns). Declining in use due to health concerns (PAH content) but still found on legacy infrastructure.

Epoxy Type	Application Method	Thickness	Max Temp	Cure	Primary Use
FBE	Electrostatic spray on heated pipe	300-600 microns	85-110°C	Seconds (heat cure)	Pipeline external/internal
Liquid epoxy	Brush, spray, roller	200-500 microns	60-120°C	Hours-days (chemical cure)	Field joints, repairs, tanks
Coal tar epoxy	Airless spray, brush	400-1000 microns	50-60°C	12-24 hours	Marine structures, legacy pipe
Novolac epoxy	Spray, brush	300-800 microns	150-230°C	Hours (chemical cure)	High-temperature service

FBE Application Process

The FBE plant coating process follows a strict sequence:

1. Surface preparation: Abrasive blasting to Sa 2.5 (near-white metal) per ISO 8501-1, surface profile 50-100 microns
2. Preheating: Induction heating to 230-245°C (temperature monitored by infrared pyrometers)
3. Powder application: Electrostatic spray guns deposit FBE powder on the hot pipe surface
4. Gel and cure: Epoxy melts, flows to uniform thickness, then cures in 30-60 seconds
5. Cooling: Water quench to below 80°C
6. Inspection: DFT measurement, holiday detection, adhesion testing

FBE is also the primer layer in 3LPE and 3LPP multi-layer coating systems, where it provides adhesion between the steel and the polyolefin topcoat.

Common Mistake

FBE coating is sensitive to UV exposure. Prolonged outdoor storage (more than 3-6 months) without UV shielding degrades the coating surface, causing chalking and reduced adhesion at field joints. Always store FBE-coated pipe under cover or with UV-protective wrapping per the manufacturer’s recommendations and ISO 21809-2.

Standards

Key standards governing epoxy coatings for pipelines include ISO 21809-2 (FBE external coatings), CSA Z245.20 (plant-applied FBE), and AWWA C213 (FBE internal linings for potable water pipe). Liquid epoxy repair coatings are typically qualified per ISO 21809-3.

For corrosion mechanisms that drive coating selection, see the guide to steel corrosion.

Read the full guide to pipe coatings