What are the details of internally and externally coated steel pipes

First, the specifications and technical parameters of internally and externally coated steel pipes

(1) Basic structure of internally and externally coated steel pipes. Internally and externally coated steel pipes use steel pipes as the base material, and a plastic anti-corrosion layer (such as epoxy resin or polyethylene) is fused onto the inner and outer surfaces through spraying, rolling, dipping, and suction processes to form a composite pipe. Its core parameters include:

Specification range of internally and externally coated steel pipes: DN15-DN1200 (some special specifications can reach DN1660), wall thickness 2-10mm, coating thickness 0.3-1.0mm (inner wall).

Connection methods of internally and externally coated steel pipes: threaded (DN15-DN100), grooved (DN65-DN400), flange (any diameter), welding, etc.

Temperature resistance of internally and externally coated steel pipes: epoxy resin coating -30℃~120℃, polyethylene coating -40℃~90℃, instantaneous temperature resistance up to 200℃ (special process).

(2) Differences in Coating Materials for Internally and Externally Coated Steel Pipes

Epoxy Resin (EP) Coating Characteristics: Resistant to chemical corrosion, high hardness, suitable for high-pressure fluid transportation. Applications include chemical engineering, fire protection, water supply, and mining.

Polyethylene (PE) Coating Characteristics: Wear-resistant and impact-resistant, good flexibility, suitable for water supply and drainage, low-pressure gas, and outdoor pipelines.

Second, Application Scenarios of Internally and Externally Coated Steel Pipes

Municipal Engineering: Water supply, drainage, and greywater reuse networks, especially suitable for corrosive soil environments.

Chemical Industry: Transporting acids, alkalis, and other media; for example, a hydrochloric acid transport pipeline in a chemical plant showed no corrosion for 5 years.

Fire Protection Systems: Pressure resistant 1.6-2.5 MPa, conforming to CJ/T 120-2016 standard.

Mining and Power: Antistatic and flame-retardant double-coated steel pipes are used for mine ventilation and drainage.

Third, Key Points for the Selection and Acceptance of Internally and Externally Coated Steel Pipes

(1) Inspection Standards for Internally and Externally Coated Steel Pipes

Coating Thickness: The inner wall thickness of internally and externally coated steel pipes should be ≥0.3mm (National Standard CJ/T120-2016), and a thickness gauge should be used for random checks.

Adhesion: No peeling should occur during the cross-cut test (ISO 2409 standard).

Electrical Spark Test: No breakdown should occur during a 1500V voltage scan.

(2) Guidelines for Avoiding Pitfalls in Internally and Externally Coated Steel Pipes

Refuse abnormally low-priced internally and externally coated steel pipes, as they may be of inferior quality.

Require a test report for the internally and externally coated steel pipes.

(3) Selection of Connection Methods for Internally and Externally Coated Steel Pipes

Small Diameter: Threaded or grooved connections for easy installation.

Large Diameter: Flanges or welding to ensure sealing.