Internal coating (thin-film) or lining (thick-film) systems protect the pipe interior from corrosion by the transported fluid, reduce friction for improved flow efficiency, and prevent product contamination.
2.1 Liquid Epoxy Internal Coating
Solvent-based or solvent-free liquid epoxy applied by spray or brush to the pipe interior. The most common internal coating for oil and gas pipelines.
Applicable Standards: API RP 5L2 (gas pipelines), ISO 15741, AWWA C210
Key Properties:
· Dry Film Thickness: 150 – 500 µm
· Temperature Range: -30°C to +90°C
· Surface Preparation: SSPC-SP10 / Sa 2½
· Holiday Detection: Per NACE TM0186 or TM0384
Advantages:
· Excellent flow efficiency improvement (reduces pipe wall roughness)
· Good resistance to CO2 and H2S corrosion
· Reduces paraffin and hydrate deposition
· Cost-effective for large-diameter pipe
Typical Applications:
· Natural gas transmission (flow efficiency, prevents internal rust during storage/construction)
· Crude oil pipelines (reduces wax deposition)
· Produced water injection lines
· Refinery product transfer lines
2.2 Fusion Bonded Epoxy (FBE) Internal Coating
Powder-applied epoxy for internal use. Similar chemistry to external FBE but formulated for fluid immersion service.
Applicable Standards: API RP 5L2, NACE SP0191
Key Properties:
· Dry Film Thickness: 300 – 500 µm
· Temperature Range: -40°C to +85°C
· Application: Electrostatic spray onto pre-heated pipe
Advantages:
· Consistent, uniform coverage
· High cross-link density (low permeability)
· Excellent chemical resistance
Typical Applications:
· Gas transmission pipelines (drag reduction, corrosion control)
· Natural gas distribution
· Produced water lines
2.3 Cement Mortar Lining (CML)
Centrifugally applied Portland cement mortar lining. The oldest pipeline lining technology, still widely used for water service.
Applicable Standards: AWWA C205, AWWA C602
Key Properties:
· Thickness: 6 – 25 mm
· Temperature Range: 5 – 50°C
· Self-Healing: Alkalinity passivates steel and prevents corrosion at small cracks or holidays
· Flow Efficiency: Improves Hazen-Williams C-factor by 15-25% vs. unlined pipe
Advantages:
· Low cost
· Long service life (50+ years documented)
· Tolerates minor surface preparation imperfections
Limitations:
· Heavy (adds significant weight to pipe)
· Not suitable for hydrocarbons
· Brittle—can crack under severe bending or impact
Typical Applications:
· Cooling water lines
· Firewater mains
· Wastewater force mains
· Potable water transmission
2.4 HDPE & Polypropylene Lining
Thermoplastic liners inserted or extruded into the pipe interior. Provide excellent chemical resistance for highly corrosive or abrasive service.
Key Properties:
Material Temperature Range Thickness Best For
HDPE -40°C to +60°C 3 – 10mm Water, mild chemicals, abrasive slurries
PP (Polypropylene) -10°C to +100°C 3 – 8mm Acid, brine, higher-temperature fluids
Advantages:
· Excellent chemical resistance
· Good abrasion/erosion resistance
· Can be field-replaced in accessible pipe sections
Typical Applications:
· Produced water with high chlorides
· Acid injection lines
· Frac flowback piping
· Chemical injection and transfer lines
2.5 Rubber Lining
Natural or synthetic rubber bonded to the pipe interior for resistance to abrasive slurries and acidic media.
Key Properties:
· Thickness: 3 – 12mm
· Temperature Range: -20°C to +120°C
· Types: Natural rubber, Neoprene, EPDM, Nitrile
Typical Applications:
· Oil sands slurry and hydrotransport lines
· Drilling mud and cuttings transfer piping
· FGD (Flue Gas Desulfurization) absorber piping in refineries
· Acid transfer lines (mild acid concentrations)
2.6 PTFE / Teflon Lining
Fluoropolymer lining for extreme chemical resistance at elevated temperatures.
Key Properties:
· Thickness: 1 – 3mm
· Temperature Range: -200°C to +260°C
· Resistance: Near-universal chemical resistance (strong oxidizing acids, solvents, caustic)
Typical Applications:
· Strong acid metering and injection lines (HF, HCl, H2SO4)
· Solvent transfer in petrochemical plants
· High-purity process applications
2.7 Glass-Reinforced Epoxy/Polyester (GRE/GRP) Lining
Fiberglass-reinforced thermoset resin lining providing structural corrosion barrier.
Key Properties:
· Thickness: 3 – 6mm
· Temperature Range: -40°C to +110°C
· Excellent Resistance to Seawater and Produced Water
Typical Applications:
· Seawater injection lines
· Produced water reinjection (PWRI)
· Firewater ring main piping
· Chemical drain systems
2.8 Alloy Overlay (Cladding / Weld Overlay)
Corrosion-resistant alloy (CRA) layer metallurgically bonded to carbon steel pipe interior. The highest-integrity internal protection for the most aggressive service.
Key Properties:
· CRA Materials: Inconel 625, 316L Stainless, Duplex, Hastelloy
· Thickness: 3 – 6mm overlay
· Temperature: Up to 800°C+
Typical Applications:
· HPHT sour gas production (H2S, CO2, chlorides)
· Acid gas injection lines
· Geothermal production (high-temperature brine)