What is erw pipe?

"ERW pipe" is a straight seam electric resistance welded pipe, abbreviated as ERW, which is used to transport vapor and liquid objects such as oil and natural gas. It can meet various requirements of high and low pressure, and occupies a pivotal position in the field of transportation pipes in the world.

The concept of ERW steel pipe

In electrical engineering, "SC" is used to indicate that it can be used as a water gas pipe or a threading pipe, and it is relatively thick.

Welded pipe is a round tube welded from steel plates. It is categorized as ERW, LSAW, and SSAW. ERW, or "high-frequency electric resistance welded steel pipe," uses a different welding process than conventional welded pipe. The weld seam is formed by melting the base steel strip, resulting in superior mechanical strength compared to conventional welded pipe. ERW, or electric resistance welding, offers high production efficiency, low cost, material savings, and ease of automation. Therefore, it is widely used in various industries, including aviation, aerospace, energy, electronics, automotive, and light industry, making it a key welding process.

Manufacturing Process

The manufacturing process for ERW pipe is relatively complex and primarily involves the following steps:

 

1. Strip Preparation

High-quality strip steel is selected as the raw material, and the strip specifications, such as thickness and width, must meet production requirements. Before entering the production line, the strip undergoes rigorous surface treatment to remove impurities such as oil and rust to ensure weld quality.

 

2. Forming Process

The steel strip is bent into a round or nearly round tube billet using a forming machine. This process requires control of forming parameters such as the bend angle and radius to ensure the tube's geometric shape and dimensional accuracy.

 

3. Welding

Using welding techniques such as high-frequency resistance welding, the edges of the tube billet are heated to a molten state. Pressure then fuses the edges together to form a weld. During the welding process, parameters such as welding current, voltage, and welding speed must be strictly controlled to ensure weld quality and strength. The welded steel pipe also undergoes weld inspection, such as flaw detection, to detect possible welding defects.

 

4. Sizing And Rounding

The welded steel pipe is adjusted in diameter using a sizing machine to achieve the required dimensional accuracy. At the same time, the steel pipe is rounded to eliminate dimensional defects such as ovality that may have occurred during the welding process.

 

5. Surface Treatment And Quality Inspection

The welded steel pipe undergoes internal and external surface cleaning and anti-corrosion treatments, such as painting and galvanizing, to improve its corrosion resistance and service life. During the quality inspection process, comprehensive testing of steel pipe dimensions, shape, weld quality, and mechanical properties is required to ensure compliance with relevant standards and customer requirements.

 

Implementation Standards

ERW pipes are widely used in the oil, gas, and construction industries, and their implementation standards are crucial for ensuring quality. The following are professional standards:

 

1. Chinese National Standard (GB)

GB/T 3091-2015

Applies to welded steel pipes for low-pressure fluid transportation. It specifies technical requirements for carbon steel (such as Q195, Q215), outer diameters of 6-219mm, and wall thicknesses of 1.2-8.0mm. The tensile strength must be ≥335MPa (see Section 5.2 of the standard).

 

GB/T 13793-2016

Regarding the dimensional and weight tolerances for straight seam electric welded steel pipes, the allowable deviation for the outer diameter is ±0.5% (DN ≤ 168mm).

 

2. International Standards

ASTM A53/A53M-2022 (American Society for Testing and Materials)

Divided into two grades, A and B. Grade B requires a yield strength of ≥240 MPa and is suitable for high-temperature and high-pressure environments (such as oil pipelines).

 

API 5L (American Petroleum Institute)

Covered by two product grades, PSL1 and PSL2. PSL2 requires more stringent impact toughness requirements (specific impact energy ≥27 J at -20°C).

 

Differences Between ERW Pipe And Other Welded Steel Pipes

1. Production Process

ERW pipe is produced by heating the edges of the strip to a molten state using high-frequency current, followed by extrusion welding. This boasts high welding speed and production efficiency, making it suitable for large-scale industrial production. Other welded steel pipes, such as submerged arc welded pipe, utilize a submerged arc welding process. The welding wire and workpiece serve as electrodes, generating an arc beneath a flux layer that melts the wire and workpiece, forming a weld. This process offers relatively high welding quality, but its production efficiency is lower than that of ERW pipe.

 

2. Weld Quality

ERW pipe has a relatively narrow weld seam and a small heat-affected zone, resulting in relatively stable mechanical properties. However, this requires high-quality raw materials, otherwise weld defects are more likely to occur. Submerged arc welded steel pipe has a wider weld seam and a larger heat-affected zone, but due to the use of flux protection during welding, the weld quality is generally more reliable.

 

3. Applications

Due to its high production efficiency and low cost, ERW pipe is often used in pipelines for fluids with low pressure requirements, such as building water supply and drainage, and gas transportation. Submerged arc welded steel pipe, due to its excellent welding quality, is often used in oil and natural gas transportation, which requires higher quality pipelines.

Read more ：The basic principle of electric resistance welded tube