3LPE Anti-corrosion Steel Pipe

• ​Introduction

3LPE (Three-Layer Polyethylene) Anti-corrosion Steel Pipe is a high-performance anti-corrosion pipe that forms a “three-layer integrated protective structure” on the outer surface of the base steel pipe: inner layer of Fusion-Bonded Epoxy (FBE), middle layer of copolymer adhesive, and outer layer of high-density polyethylene (HDPE). Unlike single-layer or double-layer anti-corrosion pipes, its three layers work synergistically: the FBE layer provides strong adhesion and chemical resistance, the adhesive layer ensures tight bonding between FBE and HDPE, and the HDPE layer offers excellent impact resistance and environmental barrier performance. It is recognized as the “gold standard” for anti-corrosion of buried oil and gas pipelines globally, and is also widely used in high-demand scenarios such as municipal high-pressure water supply and cross-river/sea pipelines.

• ​Main Functions

Superior Corrosion Resistance: The three-layer structure forms a “multi-barrier system”—FBE blocks chemical corrosion (e.g., soil acids/alkalis), the adhesive layer prevents interface peeling, and HDPE isolates moisture, oxygen, and microorganisms, achieving a corrosion rate of ≤0.01 mm/year in harsh environments.​

Excellent Mechanical Protection: The HDPE outer layer has high impact strength (passes 1.5J impact test at -30℃) and wear resistance, effectively resisting external damage during pipeline transportation, burial, or soil settlement.​

Long-term Stability in Extreme Environments: It maintains stable performance in extreme conditions such as low temperature (-40℃), high temperature (80℃), high salinity (coastal soil), and high humidity (tropical rainforests), with a service life of up to 30-50 years .​

Reliable Sealing & Leak Prevention: The integrated three-layer structure eliminates gaps between layers, avoiding “local corrosion” caused by medium penetration; it is especially suitable for high-pressure oil and gas transmission .​

Reduced Maintenance Costs: Due to its strong anti-corrosion and anti-damage capabilities, the pipe requires no regular anti-corrosion maintenance during operation, reducing long-term operation and maintenance expenses by 40%-60%.

• ​Tubing Standards

ISO 21809-1； ASTM A53，ASTM A106，API 5L ； EN 10255，EN 10240，EN ISO 21809-1； GB/T 3091，GB/T 13793，GB/T 9711，GB/T 8163，GB/T 23257.

• ​Material & Performance

Base Material: ASTM A53: Grade A、B，ASTM A106: Grade A、B、C； EN 10255: S195T、S235JRH、S275JRH、S355JRH； GB/T 3091: Q215A/B、Q235A/B、Q355B, GB/T 8163：10#，20#，Q355，Q420， GB/T 13793: Q195、Q215A/B、Q235A/B、Q355B、Q390B；

Anti-corrosion Coating: Three-Layer Polyethylene（3LPE）-Inner Layer：Fusion-bonded epoxy powder（FBE）；Middle Layer：Adhesive；Outer Layer：High-density polyethylene(HDPE).

Thickness: Total thickness: ordinary grade ≥2.0mm, enhanced grade ≥2.5mm

Key Performance : Strong Adhesion – Excellent bonding between the coating and steel pipe, with no interlayer peeling to ensure structural integrity. High Impact Resistance – Good toughness even at low temperatures, capable of withstanding mechanical impacts during transportation and construction. High Coating Integrity – Dense and uniform coating structure, free of pinholes or leaks to block the penetration of corrosive media. Strong Chemical Resistance – Resistant to erosion from acids, alkalis, and salts, suitable for long-term service in buried or submerged harsh environments. Relatively High Temperature Resistance – Stable performance under temperature fluctuations, no cracking or peeling in both low-temperature and high-temperature conditions.

• ​Manufacturing Process

Base Pipe Pretreatment: Inspection – Check the base pipe’s outer diameter, wall thickness, and surface defects (e.g., cracks, pits).​ Derusting & Degreasing – Use shot blasting equipment to treat the outer surface (reach Sa 2.5 grade, surface roughness 40-80μm) to remove rust, oxide scale, and oil; ensure the surface is clean and rough for FBE adhesion.​

Induction Preheating: Feed the pretreated pipe into an induction heating furnace; heat it to 180-220℃ (temperature deviation ≤±5℃) to activate the epoxy powder and ensure rapid melting and curing.​

Three-layer Coating Application: First Layer (FBE Spraying) – Spray fusion-bonded epoxy powder onto the hot pipe surface via an electrostatic spray gun; the powder melts instantly and forms a uniform FBE layer (80-120μm) as the pipe rotates.​ Second Layer (Adhesive Extrusion) – Immediately extrude molten copolymer adhesive (temperature 200-230℃) onto the semi-cured FBE layer using an annular extruder; the adhesive fills surface micro-pores and forms a bonding layer (170-250μm).​ Third Layer (HDPE Extrusion) – Extrude high-temperature molten HDPE (temperature 220-250℃) onto the adhesive layer via a large-diameter extruder; use a sizing sleeve and vacuum cooling to form a dense, smooth HDPE outer layer (1.8-3.0mm, depending on grade).​

Integrated Curing & Cooling: Pass the coated pipe through a curing oven (temperature 200-230℃) for 5-10 minutes to fully cure the FBE, adhesive, and HDPE layers, ensuring interlayer bonding strength.​ Cool the pipe to room temperature using staged cooling (air cooling first, then water cooling) to avoid coating cracking caused by rapid temperature changes; control the cooling rate ≤5℃/min.​

Strict Quality Inspection: Appearance Inspection – Check for defects such as bubbles, pinholes, or uneven thickness; the coating surface should be smooth and uniform.​ Thickness Test – Use an ultrasonic thickness gauge to measure each layer’s thickness (compliance with standard requirements).​ Adhesion Test – Conduct a peel test on random samples (≥30 N/cm) and a impact test (-30℃, 1.5J) to verify mechanical performance.​ Holiday Test – Use a high-voltage detector (5kV/10kV) to scan the entire pipe surface; ensure no electrical breakdown (pinholes) occurs.

• Specifications