What are the manufacturing processes for internally and externally coated steel pipes?

What Is Internally and Externally Coated Steel Pipe?

Internally and externally coated steel pipe is a composite pipeline product formed by applying anti-corrosion coatings to both the inner and outer surfaces of a steel pipe.

Typical coating materials include:

Epoxy resin (FBE, liquid epoxy)

Polyethylene (PE / 3PE)

Polypropylene (PP)

This structure combines:

The mechanical strength of steel

The corrosion resistance of polymers

Manufacturing Process of Coated Steel Pipes

1. Surface Preparation (Critical Step)

Shot blasting or sand blasting

Surface cleanliness reaches Sa2.5 or higher

Purpose:
Ensure strong adhesion between coating and steel substrate.

2. Steel Pipe Heating

Induction or furnace heating

Temperature typically controlled between 180°C–250°C

Purpose:
Activate surface energy and improve coating bonding strength.

3. Internal Coating Application

Common methods:

Spray coating (epoxy powder or liquid epoxy)

Centrifugal coating (for uniform inner wall coverage)

Key features:

Smooth internal surface

Reduced fluid resistance

Anti-scaling performance

4. External Coating Application

Depending on system requirements:

Fusion Bonded Epoxy (FBE)

2PE / 3PE coating (epoxy + adhesive + polyethylene)

Benefits:

Strong corrosion protection

Resistance to soil, moisture, and chemicals

5. Curing and Cooling

Natural cooling or forced cooling

Coating solidifies and bonds tightly

Result:
Durable composite structure with long service life.

6. Inspection and Quality Control

Coating thickness testing

Holiday (pinhole) detection

Adhesion testing

Hydrostatic pressure testing

Key Advantages for Water Supply and Drainage Systems

1. Corrosion Resistance

Resistant to acids, alkalis, and salts

Suitable for underground and humid environments

2. High Pressure Resistance

Steel substrate ensures structural strength

Suitable for municipal and industrial pipelines

3. Wear Resistance

Coated surface reduces internal abrasion

Extends pipeline lifespan

4. Anti-Scaling Performance

Smooth inner wall prevents deposits

Reduces maintenance frequency

Maintenance Cost Structure of Coated Steel Pipes

1. Labor Costs

Routine inspection

Leak detection

Valve and joint maintenance

2. Material Costs

Coating repair

Pipe replacement

Spare parts

3. Equipment Costs

Inspection instruments

Cleaning systems

Repair tools

How to Reduce Maintenance Costs of Coated Steel Pipes

1. Preventive Inspection

Regular monitoring prevents major failures

2. High-Performance Coatings

Use epoxy or multi-layer PE systems

Extend service life

3. Optimized Maintenance Workflow

Standardized procedures

Reduced downtime and resource waste

Pressure Range of Large-Diameter Coated Steel Pipes

The pressure capacity depends on:

Pipe material (carbon steel, alloy steel)

Wall thickness

Diameter (DN size)

Installation quality

Engineering Note:

Must comply with standards such as ASTM, EN, or API

Pressure rating should be verified during design calculations

Environmental factors (soil load, temperature) must be considered

Can Coated Steel Pipes Resist Chemical Corrosion?

1. Coating Barrier Protection

Plastic or epoxy layer isolates steel from corrosive media

2. Material Properties

Steel provides strength

Coating provides:

Chemical resistance

Aging resistance

Flame retardancy

3. Adaptability

Suitable for:

Municipal water supply

Fire protection systems

HVAC pipelines

Industrial fluid transport

Typical Application Scenarios of Coated Steel Pipes

Urban water supply systems

Drainage and sewage pipelines

Firefighting systems

Chemical fluid transport

HVAC and infrastructure projects

Conclusion

Internally and externally coated steel pipes combine mechanical strength, corrosion resistance, and long service life, making them a preferred solution for modern pipeline systems.

Union Steel Industry provides:

Epoxy and polyethylene coated steel pipes

Custom specifications (diameter, thickness, coating type)

Full quality inspection and global delivery

FAQ

Q1: What is the main purpose of coating steel pipes?
To prevent corrosion, extend service life, and improve flow efficiency.

Q2: Which coating is better, epoxy or polyethylene?
Epoxy offers strong adhesion and chemical resistance; polyethylene provides superior external protection and durability.

Q3: How long do coated steel pipes last?
Typically 20–50 years depending on environment and coating type.

Q4: What is the most critical step in manufacturing?
Surface preparation, as it directly affects coating adhesion and durability.