How Are ERW Pipes Manufactured?

ERW Steel Pipe Overview

Electrical resistance welded (ERW) pipe is a type of welded pipe. They are made from high-quality steel coils through a forming process. A series of rollers roll a flat steel coil or ring into a cylindrical shape. Then, electricity is applied to heat the edges of the pipe, achieving seam welding.

 

ERW steel pipes commonly use the following materials:

Low carbon steel (most commonly used): easy to weld, good plasticity, excellent formability

Stainless steel (for specific media requirements): strong corrosion resistance but higher cost

 

Some manufacturers also coat the inside and outside of the pipe with FBE fusion-bonded epoxy powder coating, significantly improving its corrosion resistance, suitable for long-term outdoor or buried environments such as oil and gas, water treatment, and structural engineering.

 

ERW Steel Pipe Manufacturing Process

The manufacturing process of ERW welded pipes is indeed quite complex. It involves multiple steps to process a flat steel coil into a pipe shape. Let's delve into the detailed manufacturing process of these welded pipes and explain it step by step.

 

1. Raw Material Preparation

First, you need to prepare a sufficiently long roll of high-quality steel. The length of this steel coil must be sufficient to produce a steel pipe of adequate length. Note that various types of steel are available on the market, each with different carbon contents, some with lower carbon content.

 

You should choose low-carbon steel because it has many advantages.

First, this steel is easy to weld without any problems.

Furthermore, its forming process is safe and it won't crack under the rollers.

If you choose high-carbon steel, it is not suitable for welding, requiring a higher current during welding, thus increasing production costs.

 

Tip: Steel pipes with a carbon content higher than 0.6% are more rigid and prone to cracking during welding, resulting in poor weld quality and easy breakage.

 

2. Steel Strip Forming

This is one of the most critical steps in the ERW welded pipe manufacturing process. First, the flat steel coil undergoes an edge trimming process. These steel strips are irregular in shape and size, and the edge trimming process removes these irregularities. If these edges are not cut and ground, the weld strength will be very low.

 

Therefore, you should carefully inspect the strip edges. If any minor irregularities are found, be sure to repair them. This pipe uses a solid welding process. However, due to the irregularities at the edges of the strips, the weld quality may be affected, thus impacting the overall quality of the pipe.

 

3. Welding Process

The formed circular pipe blank enters a high-frequency welding machine (HFW welder).

 

High-frequency welding process:

High-frequency current generates resistance heat at the edges of the pipe blank;

The edges are heated to a molten state;

Pressure is applied by squeeze rollers to form a metallurgical bond;

No welding wire or filler metal is required during the welding process;

The outer and inner weld ribs are selectively removed after welding (outer or inner rib removal) depending on the application.

 

The advantages of high-frequency welding are high welding speed, small heat-affected zone, continuous and dense weld metal, and weld strength equivalent to the base material.

 

4. Heat Treatment

These ERW welded pipes are extremely durable and robust. Heat treatment is the primary reason for their durability. The welded pipe is heated to a high temperature and then cooled in air, resulting in a significant temperature change.

 

The effects of heat treatment:

Eliminate welding stress;

Improve grain structure, resulting in a more uniform weld;

Enable weld strength to reach or exceed that of the base material;

Improve pressure resistance.

 

Therefore, ERW steel pipes can be safely used for pressurized transportation, such as urban water supply, fire protection systems, and oil and gas gathering and transportation.

 

5. Dimensioning and Cutting

After heat treatment, the pipes are ready for use. Manufacturers use sizing mills for cutting. These mills are highly efficient, ensuring precise pipe diameter and roundness.

 

You can cut ERW welded pipes into any number of sections as needed. There are no size restrictions for these pipes.

 

6. Inspection and Quality Control

A quality control system is crucial to every production process. It acts as an additional quality check, ensuring customers do not receive substandard pipes.

Eddy Current Testing (ECT): Detects weld defects.

Ultrasonic Testing (UT): Inspects for internal cracks.

Hydrostatic Testing: Tests pressure resistance.

Dimensional Inspection: Outer diameter, wall thickness, roundness.

Surface Inspection: Locates scratches, cracks, and shrinkage cavities. Mechanical property testing: tensile, bending, and impact testing.

 

Comparison with Other Types of Steel Pipes

1. ERW Steel Pipes Vs. Seamless Steel Pipes

Unlike ERW steel pipes, these seamless steel pipes have no weld seams. They are formed by extruding a single piece of steel billet, not by welding.

 

Seamless steel pipes are strong and durable because they have no weld seams, making them less prone to rust. However, they are also more expensive.

 

2. ERW Steel Pipes Vs. Spiral Welded Steel Pipes

These spiral pipes are not as good as seamless pipes. The steel plates are welded in a spiral pattern, and the weld seams are clearly visible. This type of pipe is made using this welding process.

 

However, the weld seams on these pipes reduce their strength. They are cheaper than seamless steel pipes but more expensive than ERW steel pipes.