External coatings form the primary barrier between the steel pipe surface and the surrounding environment (soil, water, atmosphere). They work in conjunction with cathodic protection (CP) systems to prevent external corrosion.
1.1 Three-Layer Polyethylene (3LPE)
The global standard for buried onshore oil and gas pipelines. A multi-layer system combining corrosion protection, adhesion, and mechanical strength.
Layer Material Typical Thickness Function
Layer 1 Fusion Bonded Epoxy (FBE) 150 µm Anti-corrosion barrier, excellent adhesion to blasted steel
Layer 2 Copolymer Adhesive 200 µm Tie layer bonding FBE to PE topcoat
Layer 3 Polyethylene (MDPE/HDPE) 1.6 – 2.95 mm Mechanical protection against impact, penetration, and soil stress
Applicable Standards: ISO 21809-1, DIN 30670, CAN/CSA Z245.21, NFA 49-710
Key Properties:
· Maximum Operating Temperature: up to +80°C
· Pipe Diameter Range: 2″ (60.3mm) to 56″ (1,422mm)
· Surface Preparation: SSPC-SP10 / NACE No.2 / ISO 8501-1 Sa 2½ (near-white metal blast cleaning)
· Holiday Detection: Per NACE SP0490 (25-30 kV depending on coating thickness)
Typical Applications:
· Cross-country oil and gas trunk pipelines
· Gas distribution networks
· Produced water gathering lines
· Flowlines (moderate temperature)
1.2 Three-Layer Polypropylene (3LPP)
The high-temperature counterpart to 3LPE. Used where elevated operating temperatures or thermal cycling exceed the capability of polyethylene.
Layer Material Typical Thickness Function
Layer 1 Fusion Bonded Epoxy (FBE) 150 µm Anti-corrosion barrier
Layer 2 Copolymer Adhesive 200 µm Tie layer
Layer 3 Polypropylene (MDPP/HDPP) 1.6 – 2.95 mm High-temperature mechanical protection
Applicable Standards: ISO 21809-1, DIN 30678, NFA 49-711, SHELL DEP 31.40.30.31-CSPC
Key Properties:
· Maximum Operating Temperature: up to +110°C (140°C for short-term excursions)
· Pipe Diameter Range: 2″ to 56″
· Total Coating Thickness: < 3.0 mm for pipe diameter < 24″; 3.3 mm for 32″ and above
· Surface Preparation: SSPC-SP10 / NACE No.2 / ISO 8501-1 Sa 2½
Typical Applications:
· High-temperature oil export lines
· Steam injection flowlines (thermal EOR)
· Offshore risers (high-temperature service)
· Deepwater flowlines (insulation grade 3LPP available)
· Compressor station discharge piping
3LPE vs. 3LPP Selection:
Parameter 3LPE 3LPP
Maximum Operating Temp 80°C 110°C
Cost Lower Higher
Impact Resistance Excellent Good
Soil Stress Resistance Good Excellent
UV Resistance Limited (store covered) Better
Typical Use Onshore burial High-temp, offshore, deepwater
1.3 Fusion Bonded Epoxy (FBE) — Single Layer
A thermosetting epoxy powder applied to pre-heated pipe, forming a continuous, highly adherent corrosion barrier.
Applicable Standards: CAN/CSA Z245.20, NACE RP0394, ISO 21809-2
Key Properties:
· Dry Film Thickness: 300 – 500 µm (standard); 500 – 1000 µm (heavy-duty)
· Maximum Operating Temperature: up to +80°C to +100°C
· Surface Preparation: SSPC-SP10 / NACE No.2 / Sa 2½
· Holiday Detection: Per NACE SP0490 (1,500 – 2,000 V for 10-30 mils)
Advantages:
· Excellent adhesion to steel (no adhesive layer required)
· High resistance to cathodic disbondment
· Tolerates pipe bending and field handling
· Lower profile than 3-layer systems (easier to handle)
Limitations:
· More brittle than 3LPE/3LPP
· Lower impact and abrasion resistance
· Moisture absorption at elevated temperature
Typical Applications:
· Directional drilling pullback sections
· Plant and station piping (above ground and buried)
· Pipeline bends and fittings
· Where 3-layer systems are cost-prohibitive
1.4 Dual-Layer FBE (D-FBE)
Two-layer FBE system combining corrosion protection with enhanced mechanical protection.
Layer Function
Layer 1 (Base Coat) Standard FBE for corrosion protection and adhesion
Layer 2 (Top Coat) Modified FBE with enhanced impact, gouge, and handling resistance
Applicable Standards: CAN/CSA Z245.20, NACE RP0394
Key Properties:
· Total Thickness: 500 – 1,000 µm
· Maximum Operating Temperature: up to +80°C to +100°C
· Superior Impact Resistance vs. single-layer FBE
· Better Gouge Resistance during handling and installation
Typical Applications:
· Directional drilling and trenchless installation
· Rocky terrain burial
· Offshore platform piping
· Where 3LPE is specified but FBE handling advantages are desired
1.5 Coal Tar Enamel (CTE)
Traditional coating system composed of coal tar pitch with reinforcing glass fiber inner and outer wraps.
Key Properties:
· Thickness: 3.0 – 5.0 mm
· Maximum Operating Temperature: up to 60°C
· Excellent Resistance to Water Absorption
· Good Adhesion to Steel
Limitations:
· Health and environmental concerns during application (volatile organic compounds)
· Low temperature flexibility (brittle in arctic conditions)
· Mostly phased out in favor of 3LPE/FBE in new construction except for specific water pipeline service
Typical Applications:
· Legacy pipeline maintenance and repair
· Water injection and disposal lines
· Cooling water pipelines
1.6 Concrete Weight Coating (CWC)
Not a corrosion coating—CWC is applied over a corrosion coating (typically 3LPE or FBE) to provide negative buoyancy and mechanical protection for subsea pipelines.
Key Properties:
· Thickness: 25 – 150 mm (engineered per pipeline buoyancy requirements)
· Density: 2,400 – 3,050 kg/m³ (standard), up to 3,450 kg/m³ (high-density/heavyweight)
· Reinforcement: Welded wire mesh (cage) embedded within concrete
· Application: Impingement/compression method or wrap-around method
Typical Applications:
· Subsea pipelines requiring on-bottom stability
· River and waterway crossings
· Offshore platform approaches
· Shore pull sections