Difference between Seam Pipe and Seamless Pipe

There are many kinds of steel pipes on the market, such as: seam pipes, seamless pipes, etc., but many people do not know the difference, so what is the difference between seamed steel pipes and seamless steel pipes?

Seamed Steel Pipe:

A seamed steel pipe, also known as a welded steel pipe, is a type of pipe made from hot-rolled steel strip or plate as raw material, cold-bent, and then welded. Based on the welding method, it is mainly divided into:

●ERW (Electrical Resistance Welded Pipe): High-frequency resistance welding, high efficiency, suitable for small and medium diameters.
●LSAW (Straight Seam Submerged Arc Welded Pipe): Steel plate is formed and then submerged arc welded, suitable for large diameters and thick walls.
●SSAW (Spiral Submerged Arc Welded Pipe): Steel strip is spirally formed and then submerged arc welded; large diameter pipes can be produced using narrow steel strips.

Common names:
Galvanized welded steel pipe: Commonly known as "white iron pipe" on construction sites, it has a galvanized layer, good corrosion resistance, and is used outdoors, in fire protection, and in humid environments.
Ungalvanized welded steel pipe: Commonly known as "black iron pipe," its surface has an oxide scale color, used in dry indoor environments, and requires painting for corrosion protection.

Specifications:
Common nominal diameter: DN15~DN600 (1/2"~24")
Maximum nominal diameter: Up to DN4000 (160 inches) and above (e.g., large-diameter spiral welded pipe)

Seamless Steel Pipe:

Seamless steel pipes are steel pipes made from solid round steel billets through processes such as piercing, hot rolling, cold drawing, or extrusion, resulting in a pipe body without any weld seams.

● Based on the production method, seamless steel pipes can be divided into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, and extruded seamless steel pipes.
● Based on the cross-sectional shape, seamless steel pipes can be divided into round and irregular-shaped types.
● Based on wall thickness, seamless steel pipes are further divided into thin-walled seamless steel pipes (D/t ≥ 20) and thick-walled seamless steel pipes (D/t < 20). Thin-walled pipes are used for lightweight structures, while thick-walled pipes are used for high-pressure bearing components.
● Based on different applications, seamless steel pipes are mainly used as fluid transport pipes, structural pipes, boiler tubes, oil well tubes, precision tubes, etc.

Specification Range: 

Seamless steel pipes have an extremely wide specification range, with a minimum outer diameter of 1.6mm (precision capillary tube) and a maximum outer diameter of 1620mm; wall thicknesses range from 0.25mm to over 150mm.

Differences between Seamed Steel Pipes and Seamless Steel Pipes:

1. Appearance
The inner wall of seamed steel pipes usually shows a noticeable weld reinforcement (ERW pipes have smooth welds, LSAW pipes have prominent welds); seamless steel pipes have a smooth, continuous inner wall without any weld marks.

2. Pressure Resistance
Due to its seamless, integral structure, seamless steel pipes generally have better pressure resistance and fatigue resistance than welded steel pipes under the same material and wall thickness conditions, making them particularly suitable for high-pressure, high-temperature, and alternating load conditions. However, modern high-performance seamed steel pipes (such as LSAW and ERW) can also be used in medium- and high-pressure applications through strict quality control. Specific pressure resistance values need to be calculated according to standard formulas.

3. Applications
Seamed steel pipes are widely used for low-pressure fluid transportation, building structures, and general engineering due to their low cost and high production efficiency; seamless steel pipes, due to their strong integrity and high reliability, are mainly used in high-pressure boilers, petrochemicals, hydraulic systems, precision machinery, and other fields with stringent safety and performance requirements. While their applications overlap, seamless steel pipes are irreplaceable in high-end fields.

4. Different Manufacturing Processes
Seamed steel pipes: Made from steel plates/strips, cold-bent into a tubular shape, and then welded using high-frequency electric resistance welding (ERW) or submerged arc welding (SAW).
Seamless steel pipes: Made from solid steel billets, formed integrally through multiple processes including heated piercing, rolling (hot rolling/cold drawing/cold rolling), and heat treatment.

5. Price Differences
Compared to seamed steel pipes, seamless steel pipes are more expensive, primarily due to their more complex processing, lower yield, and stricter quality control. Their price is typically 30%-100% higher than seamed steel pipes of the same specifications, depending on the material grade, dimensions, and delivery condition.

Seamed steel pipes have a simpler manufacturing process and wider applications, thus their price is relatively lower.

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