I. Introduction to 3PE Anti-Corrosion Coated Steel Pipe
3PE anti-corrosion coated steel pipe is a composite pipe with a three-layer polyethylene anti-corrosion coating applied to the outer surface of the steel pipe.
This product is widely used in oil, natural gas, water, heat transmission, and chemical media pipeline systems, offering excellent corrosion resistance, resistance to mechanical damage, and a long service life.
II. Introduction to 3PE Anti-Corrosion Structure
3PE Anti-Corrosion Coated Steel Pipe Structure: Steel Pipe Base → Epoxy Powder Layer (Anti-Corrosion) → Adhesive Layer (Bonding) → Polyethylene Layer (Protection)
| Layer | Material | Main Function | Thickness Range (Reference) |
|---|---|---|---|
| First Layer (Inner Layer) | Fused Epoxy Powder (FBE) | Provides excellent corrosion protection, firmly adheres to steel surface, prevents rust spread. | 80–150 μm |
| Second Layer (Intermediate Layer) | Copolymer Adhesive | Bonds the epoxy layer to the outer polyethylene layer firmly. | 170–250 μm |
| Third Layer (Outer Layer) | Polyethylene (PE) | Provides mechanical protection and waterproofing; wear-resistant, impact-resistant, UV-resistant. | 2–3 mm |
III. Application scope and use environment of 3PE anti-corrosion steel pipe
i. Urban water supply and drinking water transportation
3PE anti-corrosion steel pipe is commonly used in urban water supply network.
The inner epoxy coating can prevent the steel pipe from rusting and avoid secondary water pollution.
The outer polyethylene protective layer can resist corrosion from groundwater and acidic and alkaline soil.
It is suitable for long-term underground use and has a service life of more than 30 years.
Purchasing advice:
Choose food-grade epoxy powder to meet drinking water hygiene standards.
Common specifications are DN100~DN1200, and the pipe length is 6m or 12m.
ii. Long-distance oil and gas pipelines
3PE anti-corrosion steel pipe is the mainstream corrosion protection method for oil and gas pipelines.
It is resistant to acids, alkalis, salts, and corrosive media found in oil and gas.
The outer PE layer protects against mechanical impact and soil stress.
Purchasing Recommendation:
Select products that comply with API 5L or SY/T 0413 standards.
It is suitable for medium- and long-distance buried transmission systems and can be used with cathodic protection.
iii. Chemical and Industrial Circulating Water Systems
Used in circulating water networks for chemical, pharmaceutical, papermaking, and power plants.
The 3PE anti-corrosion layer protects against chemical corrosion, extending equipment life.
Suitable for conveying media containing salt, acidic or alkaline substances, or high-temperature condensate.
Purchasing Recommendations:
Preferably, choose a PE outer layer with an antistatic coating.
For high-temperature media, an epoxy-modified base layer may be required to enhance heat resistance.
iv. Submarine Pipelines and Coastal Projects
3PE corrosion-resistant steel pipe is suitable for marine and coastal environments.
It offers strong moisture and salt spray resistance, and resists seawater and sediment erosion.
It is used in projects such as cross-sea water transmission, submarine cable protection, and port oil pipelines.
Purchasing Recommendations:
Select a reinforced 3PE structure with an outer layer thickness of 3.5mm or greater.
An overlay of a scratch-resistant protective layer or concrete weighting layer is acceptable.
v. Heat Transmission and Underground Heating Systems
In central heating or underground heating projects, 3PE anti-corrosion steel pipes are used for external corrosion protection.
Combined with a polyurethane insulation layer and outer protective pipe, they form a “steel-in-steel” structure.
The anti-corrosion layer effectively prevents underground moisture from corroding the outer wall of the steel pipe.
Purchasing Recommendations:
They are often used in combination with polyurethane insulated pipes.
When purchasing, pay attention to the temperature resistance of the anti-corrosion layer (recommended ≤80°C).
IV. 3PE anti-corrosion coated steel pipe implementation standards
i. International Standards
(1) DIN 30670 (German Standard)
Title: Polyethylene Coatings on Steel Pipes and Fittings – Requirements and Testing
Content: Specifies the structural composition, coating thickness, adhesion, impact resistance, and testing methods of a three-layer polyethylene (3LPE) coating.
Features: This is the world’s earliest 3LPE standard and is used as a technical reference by many countries and companies.
Scope of Application: Buried or underwater pipelines for oil, natural gas, and water supply pipelines.
(2) ISO 21809-1 (International Standard)
Title: Petroleum and Natural Gas Industries — External Coatings for Buried or Submerged Pipelines
Content: Covers the external corrosion protection requirements for buried and underwater steel pipelines in the oil and gas industry, including three-layer polyethylene (3LPE) and three-layer polypropylene (3LPP) coating systems.
Features: This standard is a universal standard for the international oil and gas industry, applicable to international projects and export products.
ii. Chinese national and industry standards
(1) SY/T 0413-2017
Title: Technical Standard for Polyethylene Anticorrosion Coatings for Buried Steel Pipelines
Content: Specifies the materials, structure, thickness grades (standard and reinforced), and performance testing methods for 3PE anticorrosion coatings.
Features: An authoritative standard for China’s petroleum and natural gas industry, covering the entire design, construction, and acceptance process.
Scope of Application: Buried steel pipes for petroleum, natural gas, chemical media, and urban pipelines.
(2) GB/T 23257-2017
Title: Technical Standard for Polyethylene Anticorrosion Coatings for Buried Steel Pipelines
The content is essentially the same as SY/T 0413, but its scope of application is broader, including municipal, water supply and drainage, and industrial pipelines.
Features: This national standard (GB) is widely adopted in engineering projects and is suitable for domestic market procurement and project bidding.
(3) CJ/T 120-2016
Title: Technical Standard for Polyethylene Anticorrosion Coatings for Buried Steel Water Supply Pipes
Content: Specifically for use in urban water supply and drinking water delivery systems, specifies hygienic and safety requirements for epoxy powder and PE materials.
Features: Suitable for municipal water supply systems and meets drinking water safety requirements.
iii. Common exports and benchmarking standards
| Region / Standard | Name | Main Features |
|---|---|---|
| EN 10289 | European Standard for External Pipe Coating | Specifies requirements for epoxy powder and polyethylene composite layers |
| AWWA C210 / C214 | American Water Works Association Standard | Applicable for water supply and industrial pipeline external corrosion protection |
| CAN/CSA Z245.21 | Canadian Standard | Used for anti-corrosion coating of oil and gas pipelines in North America |
iv. Procurement Recommendations
For domestic projects: GB/T 23257 or SY/T 0413 are recommended.
For export or international projects: DIN 30670 or ISO 21809-1 are acceptable.
For drinking water systems: CJ/T 120 should be implemented to ensure hygienic compliance.
For high-demand projects: Suppliers are advised to provide third-party test reports, including adhesion, cathodic disbonding, and impact test data.
V. Common base pipe materials for 3PE anti-corrosion coated steel pipes
| Material Category | Common Grades | Standard | Features | Typical Applications |
|---|---|---|---|---|
| Carbon Steel Pipe | Q235B, Q345B | GB/T 8163, GB/T 9711 | Low cost, easy to weld, suitable for medium and low-pressure transport | Urban water supply, drainage, general industrial fluids |
| Line Pipe Steel (L Series) | L245, L290, L360, L415, L450, L485 | GB/T 9711 (equivalent to API 5L Gr.B~X70) | High strength, good tensile properties, strong toughness | Long-distance oil and gas pipelines |
| API Standard Steel Pipe | API 5L Gr.B, X42, X46, X52, X60, X65, X70 | API 5L | International oil and gas standard, suitable for high-pressure, long-distance transport | Oilfield development, oil transportation networks |
| Alloy Steel Pipe | 20#, 16Mn, 12CrMo, 15CrMo | ASTM A106, A335, etc. | High temperature resistance, stress corrosion resistant | Power plant steam pipelines, chemical media transport |
| Stainless Steel Pipe | 304, 316L | ASTM A312, GB/T 14976 | Excellent corrosion resistance, suitable for special media | Chemical, food, seawater desalination systems |
| Spiral Welded Pipe (SSAW) | Q235B, Q345B, L245-L485 | SY/T 5037 | Large diameter, cost-effective | Urban water supply, large-diameter buried pipelines |
| Straight Seam Welded Pipe (LSAW) | Q345B, L360, X52 and above | GB/T 9711, API 5L | High precision, excellent weld performance | High-pressure long-distance pipelines, heating networks |
VI. Inspection items and standards for 3PE anti-corrosion steel pipes
| No. | Test Item | Inspection Content | Test Method | Acceptance Criteria | Reference Standard |
|---|---|---|---|---|---|
| 1 | Appearance Inspection | Check surface for smoothness, bubbles, cracks, missed coating, and other defects | Visual inspection with lighting aid | Surface smooth, no defects affecting corrosion protection | GB/T 23257-2017 §7.1 SY/T 0413-2017 §8.1 |
| 2 | Thickness Measurement | Measure total 3PE coating thickness | Magnetic or ultrasonic thickness gauge | Thickness meets requirements; thinnest area ≥ 90% of standard value | GB/T 23257-2017 §7.2 DIN 30670 §8.2 |
| 3 | Spark Test | Check for pinholes or defects in the coating | Spark leakage detector; voltage set by U=K√T | No spark-through defects allowed | SY/T 0413-2017 §7.3 ISO 21809-1 §10.7 |
| 4 | Adhesion Test | Check bonding strength between epoxy layer, steel pipe, and adhesive layer | Peel test or cross-cut method | Peel strength ≥ 30 N/cm; no delamination or blistering | GB/T 23257-2017 §7.4 SY/T 0413-2017 §8.4 |
| 5 | Impact Test | Evaluate impact resistance of coating | Impact tester (ambient and -20℃) | No cracks, no delamination; spark test shows no defects | GB/T 23257-2017 §7.5 DIN 30670 §8.5 |
| 6 | Cathodic Disbondment Test | Check coating disbondment under cathodic protection current | Measure disbond radius after constant voltage immersion | Disbond radius ≤ 10 mm (ambient temperature) | SY/T 0413-2017 §8.6 ISO 21809-1 §10.10 |
| 7 | Ageing Resistance Test | Check coating stability under UV and high temperature | Ageing chamber test (UV + high temperature) | No chalking, cracking, or blistering | GB/T 23257-2017 §7.8 ISO 21809-1 §10.9 |
| 8 | Water Absorption Test | Check water absorption of polyethylene layer | Soak in water at ambient temperature for 24 h and weigh | Water absorption ≤ 0.03% | GB/T 23257-2017 §7.9 DIN 30670 §8.8 |
| 9 | Thermal Cycling Test | Evaluate coating stability under alternating hot and cold conditions | Cycle 10 times between hot and cold water | No blistering, delamination, or cracking | GB/T 23257-2017 §7.10 |
| 10 | Pinhole Repair Inspection | Re-inspect locally repaired areas for quality | Repeat spark test or thickness measurement | Repair area performance not lower than original coating | GB/T 23257-2017 §7.11 |
