Detailed introduction of internal plastic coated steel pipe

The following is a detailed introduction to internal plastic coated steel pipe, covering its definition, structure, process, performance, and application scenarios:

1. Definition of internal plastic coated steel pipe

Basic concept: A composite pipe with a plastic anti-corrosion layer (such as epoxy resin, polyethylene) melt-coated on the inner wall of the steel pipe, and the outer wall can retain the original steel pipe, galvanized layer or other anti-corrosion treatment (such as spraying, painting).

Design purpose: For scenes with strong internal corrosive media or high cleanliness requirements, taking into account the protection needs of the external environment, and achieving a balance between economy and functionality.

2. Production process flow of internal plastic coated steel pipe

(1) Base pipe pretreatment: - Inner wall sandblasting and rust removal (Sa2.5 grade) → cleaning → phosphating (enhanced adhesion).

(2) Internal plastic coating process:

-Electrostatic spraying: Applicable to epoxy resin powder, uniform adsorption, and high-temperature curing (180~220℃).

-Vacuum suction coating: Used for polyethylene coating, liquid PE is adsorbed and cured by negative pressure.

(3) External anti-corrosion treatment: galvanizing (hot-dip galvanizing/electroplating) or spraying anti-corrosion paint.

(4) Performance characteristics: the inner wall is resistant to acid, alkali, salt, and organic matter (depending on the type of coating), and the outer wall is rust-proof (galvanized/sprayed plastic).

The inner wall is smooth (friction coefficient ≤ 0.008), which reduces scaling and improves water/gas transmission efficiency.

The pressure bearing capacity of the base pipe remains unchanged (working pressure ≤ 2.5MPa, and can reach 10MPa with special design).

Epoxy coating: -30℃~120℃; polyethylene coating: -40℃~80℃.

The inner coating is non-toxic (in accordance with GB/T17219 drinking water hygiene standards).

(5) Application scenarios

Municipal water supply and drainage: inner wall anti-corrosion, anti-algae breeding, and extended pipeline life.

Chemical pipeline: transport acid and alkali media (such as epoxy coating resistant to concentrated sulfuric acid and hydrochloric acid).

Food/pharmaceutical industry: inner wall food-grade polyethylene (PE) coating to avoid metal ion contamination.

Gas transmission: flame-retardant epoxy coating on the inner wall, galvanized outer wall to prevent environmental corrosion.

(6) Comparison with fully plastic-coated steel pipes

Low cost (only inner wall plastic coating + simple external anti-corrosion), high cost (double plastic coating on inner and outer walls)

Weak external corrosion (such as indoors, dry areas), highly corrosive environment (chemical zone, marine climate)

The outer wall needs to be regularly inspected for galvanized/sprayed coating, full coating protection, low maintenance frequency

(7) Selection and construction recommendations

Coating selection:

Epoxy resin (EP): resistant to high temperatures and highly corrosive media (chemical pipelines).

Polyethylene (PE): wear-resistant, food-grade safety (ore slurry, drinking water).

External anti-corrosion matching:

Wet environment: galvanized outer wall + anti-corrosion paint.

Dry environment: spray ordinary anti-rust paint on the outer wall.

Construction precautions:

Welding is prohibited (destroying the coating), and a flange or groove connection is preferred.

During transportation, add a plastic sheath to the inner wall to avoid scratches by hard objects.

(8) Standards and Testing

National standards:

GB/T28897 "Steel-plastic composite pipe": coating thickness, adhesion, and impact resistance.

CJ/T120 "Plastic-coated composite steel pipe for water supply": hygienic performance and pressure test.

Key test items:

Electric spark leak detection (3kV/mm, no leak point).

Adhesion test (grid method, no peeling of coating).

Summary: Through precise anti-corrosion design, the internal plastic-coated steel pipe can meet specific working conditions while reducing the overall cost. It is especially suitable for scenarios with strong internal medium corrosion and general external environment corrosion (such as urban water supply and food industry). When selecting, the medium characteristics, environmental conditions, and budget should be considered, and the chemical resistance and adhesion indicators of the coating should be verified first.