Spiral Steel Pipe Anti-corrosion System Comprehensive Explanation

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Structure (from the steel pipe outward):

1. Bottom layer: Fusion-bonded epoxy powder FBE (static spraying, strong adhesion to the steel surface, chemical resistance, anti-anode peeling)
2. Middle layer: Copolymer adhesive (bonding the epoxy layer and PE layer together to prevent delamination)
3. Outer layer: High-density polyethylene PE (extrusion coating, mechanical protection, water and oxygen isolation, anti-bump)

Key parameters:

1. Total thickness: Ordinary grade approximately 1.8–2.5mm, reinforced grade 2.5–3.2mm, extremely reinforced grade 3.0–3.7mm (DIN 30670 / GB/T 23257)
2. Temperature resistance: Ordinary PE can withstand 60℃ for a long time, high-temperature type can withstand 80℃ for a long time; over 80℃ requires 3PP (polypropylene)
3. Design life: Normal underground burial for 30–50 years, can be used in conjunction with cathodic protection

Advantages / Disadvantages:
✅ Advantages: High mechanical strength, impact resistance, extremely strong waterproof and permeation resistance, good cathodic peeling performance, it is the international mainstream standard for buried long-distance pipelines; factory continuous production, stable quality.

❌ Disadvantages: Bare pipes for outer and inner walls ; Not heat-resistant (not acceptable above 80℃); Transportation, hoisting and bumps under the trench can easily scratch the PE layer. The quality of the joint coating determines the final lifespan. The price is higher than that of epoxy coal tar pitch.

Applicable scenarios
Underground gas, long-distance transportation of crude oil/petroleum products, natural gas gathering and transportation, external anti-corrosion for chemical media, municipal underground pipelines; not suitable as inner wall coating for drinking water (PE does not come into contact with drinking medium).

Structure

1. Outer Wall: Exactly the same as 3PE (FBE + adhesive + PE)
2. Inner Wall: Fusion-bonded epoxy powder FBE coating (thickness usually 300–500 μm)

The Essential Difference from 3PE:

Advantages/Disadvantages
✅

• The outer wall continues the strong underground protection of 3PE;
• the inner wall is FBE smooth, water-resistant, resistant to slight corrosion, not prone to scaling, and has low water flow resistance;
• both the inside and outside are protected, with a long lifespan.

❌

The FBE on the inner wall is a thin coating; it is afraid of sharp impurities scouring and is not resistant to strong acids and strong alkalis; the on-site welding joints on the inner wall are difficult to repair.

Applicable scenarios
Pressure water supply pipelines, municipal water supply, reclaimed water, circulating water, oilfield water injection, and water transportation; these are the most commonly used "full anti-corrosion" solutions for long-distance underground water supply / water transportation.

Structural Process
Epoxy coal tar coating (epoxy resin + coal tar + curing agent + anti-rust pigment), alternate base coat and top coat, with glass fiber cloth wound in the middle for reinforcement, classified by number of layers:

1. One cloth two coats: Dry film ≥ 0.4mm, for dry soil, overhead, temporary pipelines

• Two cloths three coats (enhanced grade): Dry film ≥ 0.6mm, for ordinary buried water supply/sanitation
• Three cloths five coats (super enhanced grade): Dry film ≥ 0.8mm, for saline-alkali areas, swamps, sewage plants, underwater projects

Advantages / Disadvantages
✅

• Low cost, cold application construction, can perform on-site repair and patching;
• resistant to water, dampness, certain acids and alkalis;
• flexible coating, suitable for rough construction environments.

❌

It is a thin coating, its mechanical impact resistance is much lower than 3PE;

contains coal tar, has an odor, cannot be used for drinking water inner walls;

poor UV resistance, prone to aging in outdoor and open-air environments; the corrosion protection life is generally 15–25 years, weaker than 3PE.

Applicable scenarios
Underground sewage pipes, rainwater pipes, drainage, industrial wastewater, underwater pipes, trench pipes; many projects use the combination of "inner wall IPN8710 + outer wall epoxy coal tar asphalt with three layers of fabric and five layers of oil", which is the most classic and economical configuration for municipal water supply.

What is it?

IPN = Interpenetrating Network, an interpenetrating network polymer, is a type of water-based/solvent-based anti-corrosion coating, available in multiple models:

• IPN8710-1 (primer): epoxy modified, with strong adhesion and anti-rust properties, suitable for priming
• IPN8710-2B / -2 (drinking water type topcoat): non-toxic, compliant with GB/T 17219 for drinking water hygiene, specifically for contact with domestic drinking water
• IPN8710-3 (thick paste type): resistant to acids and alkalis, anti-microbial, suitable for industrial water, sewage, outdoor structures of steel

Structures (main internal coating)

1 coat of IPN8710-1 primer + 1-2 coats of 8710-2B topcoat, with a total dry film thickness of approximately 0.2–0.3mm.
Advantages / Disadvantages

✅ Drinking water type non-toxic, smooth, anti-scaling, with good adhesion; cost lower than FBE internal coating; sprayable, flexible in construction.

❌ Thin coating, not resistant to strong flushing, not resistant to high concentration acids and alkalis; only for internal walls, external walls must be additionally coated with anti-corrosion; not resistant to high temperature.

Applicable scenarios
For drinking water, tap water, the inner walls of water tanks in bathrooms, and fire protection water pipes; it is strictly prohibited to use ordinary models (non-drinking water type) to come into contact with drinking water.

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