ERW vs. Seamless Pipe (SMLS)

In the industrial piping field, choosing between resistance welded steel pipes and seamless steel pipes is one of the most common decisions customers face. Pipe selection requires not only focusing on quality but also balancing structural integrity and project economy. With advancements in high-frequency welding (HFW) technology, the performance gap between seamless and welded steel pipes has gradually narrowed.

This article will detail the differences between the two in terms of manufacturing processes, strength, precision, and cost, helping you easily choose the right material.

1. Manufacturing Process Differences: Welded vs. Seamless

Seamless Steel Pipe (SMLS): Seamless steel pipes are made from solid cylindrical steel billets. After heating the billet to a suitable temperature, a mandrel is used to pierce the center of the billet, forming a hollow tube, which is then rolled through a rolling mill to achieve the final shape.

The main characteristics are the absence of weld seams, uniform overall pipe quality, and high strength.

ERW Steel Pipe (High-Frequency Welded Type): ERW steel pipes are made from flat steel coils. After the steel coil is unrolled, it is cold-formed into a cylinder. Then, high-frequency current (HFW) is used to heat the edges to a molten state, and pressure is used to fuse the edges together.

The main characteristic is a longitudinal weld seam running the length of the steel pipe. Due to cold forming, the wall thickness of the steel pipe is uniform, and the dimensional accuracy is high.

2. Strength and Pressure Rating (Weld Seam)

The main advantage of seamless steel pipes is that they have no weld seam and can withstand higher pressures. ERW steel pipes, due to their weld seam, have lower strength and pressure resistance than seamless steel pipes. However, with the continuous advancement of high-frequency welding technology, the gap between seamless steel pipes and ERW steel pipes is gradually narrowing.

3. Dimensional Accuracy: The Hidden Advantage of ERW Steel Pipes

Seamless welded pipes excel in pressure resistance, while ERW welded pipes excel in precision.

Wall Thickness Consistency: ERW welded pipes are made from rolled steel coils. Modern steel rolling technology achieves extremely high precision. Therefore, the wall thickness of ERW welded pipes remains consistent throughout their entire length.

The "Eccentricity" Issue of Seamless Welded Pipe: Because seamless welded pipe is stamped from steel billets, the mandrel may slightly deviate from the center during manufacturing. This results in "eccentricity"—one side of the pipe wall is thicker than the other.

Importance: For welding alignment, automated threading, or high-speed machining (e.g., automotive parts), the superior concentricity of ERW pipe is a significant operational advantage.

4. Cost and Delivery Time

Price: ERW pipe is typically 20% to 30% cheaper per ton than seamless pipe. This is because its manufacturing process is simpler, consumes less energy, and is faster.

Supply: ERW production is continuous and fast. Large orders for standard sizes (e.g., 6 inches to 24 inches) can be fulfilled much faster than seamless pipe orders, which typically have longer lead times due to the complex billet processing.

Large Diameter: Producing seamless pipe with a diameter exceeding 24 inches (600 mm) is very difficult, and the cost increases exponentially. ERW (and LSAW) became the only viable option for large-diameter pipelines.

5. Comparison Summary Table

Feature	ERW Pipe (HFW)	Seamless Pipe (SMLS)	Winner
Pressure Rating	Low to High (Limitations exist)	Extreme High Pressure	Seamless
Cost	Low (Budget Friendly)	High	ERW
Wall Tolerance	Tight, Consistent	Varies (Eccentricity issues)	ERW
Availability	Fast Lead Time	Longer Lead Time	ERW
Diameter Range	Broad (1/2" - 24"+)	Limited (Best < 20")	ERW
Aesthetics	Visible Seam (unless treated)	Smooth, Uniform	Seamless

Summary

Seamless steel and ERW are not inherently superior or inferior; rather, a balance must be struck based on cost, pressure rating, and precision requirements. Understanding the differences in their manufacturing processes and performance will help you select the appropriate steel pipe type for your project more quickly and accurately.