Spiral steel pipes and straight seam welded steel pipes are two of the most commonly used welded pipe products in large-scale pipeline and structural applications. While both rely on advanced welding technologies to achieve reliable mechanical performance, their manufacturing processes, welding methods, and application characteristics differ significantly. Understanding these differences is essential when selecting the most appropriate pipe type for a specific project.
1. Welding Process Comparison
Spiral Steel Pipes: Submerged Arc Welding (SAW)
Spiral steel pipes are typically manufactured using submerged arc welding (SAW). In this process, a continuous welding wire serves as both the electrode and filler material. During welding, the arc burns beneath a layer of granular flux that completely covers the welding zone.
Under the intense heat of the arc:
The wire tip and part of the base metal melt to form the weld pool.
The flux partially melts into slag, which floats on the surface of the molten metal.
This slag layer isolates the weld metal from atmospheric contamination, preventing oxidation and nitrogen absorption.
A metallurgical reaction occurs between the slag and molten metal, helping refine the weld composition and improve mechanical properties.
The insulating slag layer slows the cooling rate, reducing residual stress and the risk of cracking.
Submerged arc welding supports high welding currents, resulting in deep penetration, uniform welds, and excellent consistency. Combined with a high level of automation, SAW makes spiral steel pipes particularly suitable for large-diameter and thick-walled pipelines, such as oil and gas transmission lines, water pipelines, and structural applications. The process is widely used for carbon steel, low-alloy structural steel, and even certain stainless steel grades.
Straight Seam Welded Steel Pipes: High-Frequency Welding (HFW)
Straight seam welded steel pipes are commonly produced using high-frequency welding (HFW), also referred to as high-frequency resistance welding. This is a solid-state welding process, meaning the metal is not fully melted during bonding.
Depending on how heat is generated, HFW can be divided into:
Contact high-frequency welding, where high-frequency current is introduced into the workpiece through mechanical contact.
Induction high-frequency welding, where an external induction coil generates eddy currents within the steel strip via electromagnetic coupling.
In both cases, resistance heat generated by the high-frequency current rapidly raises the temperature of the strip edges to a molten or near-plastic state. The edges are then pressed together—often with an upsetting force—to form a solid metallurgical bond.
High-frequency welding is characterized by:
Extremely high production efficiency, with welding speeds reaching up to 30 m/min.
A narrow heat-affected zone (HAZ), which helps maintain base metal properties.
The need for highly specialized equipment, typically designed for specific pipe diameters and wall thickness ranges.
2. Structural and Performance Differences
Spiral Steel Pipes
Weld seam follows a helical path, distributing stress more evenly around the pipe.
Better adaptability to large diameters and varying wall thicknesses.
High weld reliability due to deep penetration and slow cooling.
Slightly longer weld length compared to straight seam pipes of the same diameter.
Straight Seam Welded Steel Pipes
Weld seam runs parallel to the pipe axis.
High dimensional accuracy and good surface finish.
Superior efficiency for mass production of small- to medium-diameter pipes.
Weld quality is highly dependent on precise process control and edge preparation.
3. Application Scenarios
Spiral steel pipes are preferred for:
Long-distance oil and gas pipelines
Large-diameter water transmission projects
Piling, bridge structures, and offshore engineering
Applications requiring high pressure-bearing capacity and structural stability
Straight seam welded steel pipes are commonly used in:
Urban gas distribution networks
Structural columns and building frameworks
Mechanical and automotive components
Projects requiring high production efficiency and dimensional consistency
4. Summary
In essence, the difference between spiral steel pipes and straight seam welded steel pipes lies in their welding technology, structural characteristics, and production focus. Submerged arc welded spiral pipes emphasize weld integrity and large-diameter capability, while high-frequency welded straight seam pipes prioritize production speed and dimensional precision. Selecting the right type depends on project scale, pressure requirements, cost considerations, and long-term performance expectations.
United Steel Industry As the most important steel pipe manufacturer and exporter in China, in the past 20 years, we have completed more than 100 projects, with partners in more than 100 countries, and established relationships with oil and gas and EPC companies in many countries business relationship.
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please consult:Email:Sales@usisteels.com
