1. Overall Comparison of Manufacturing Processes
1.1. Fundamental Differences in Forming Methods
Longitudinal submerged arc welded (LSAW) steel pipes are formed by directly shaping steel plates along their length. The plates are pre-bent, shaped, and welded, with the weld seam aligned along the same straight line of the pipe. This method ensures a short forming path, uniform stress release in the steel plate, and high geometric accuracy. In contrast, spiral welded pipes are formed by continuously rolling steel strips at a specific spiral angle and then welding them. The weld seam is spirally distributed around the pipe surface. This process is more continuous but may lead to amplified geometric deviations, particularly with larger diameters.
1.2. Differences in Raw Materials: Steel Plates vs. Steel Strips
LSAW steel pipes typically use wide, fixed-width medium-thick steel plates, providing more stable material properties and thickness control. Spiral welded pipes, on the other hand, are made from coiled steel strips, which must be uncoiled, straightened, and cut to size, leading to slight variations in material consistency between batches. As a result, LSAW steel pipes start with a higher degree of dimensional consistency at the outset of production.
2. Differences in Welding Processes
2.1. Weld Seam Distribution and Energy Input
LSAW steel pipes feature a single or double longitudinal weld seam, with short weld lengths and concentrated energy input, allowing precise control over the welding process and weld structure. Spiral welded pipes have longer weld seams, which distribute energy input over a larger area, requiring greater attention to heat-affected zone management. The longer the weld seam, the higher the likelihood of defects, making LSAW pipes more reliable in terms of welding quality.
2.2. Welding Equipment and Weld Seam Structure
LSAW steel pipes use internal and external submerged arc welding for single-pass welding, which ensures a high level of automation and consistent weld penetration. The welds are generally uniform and deep. In comparison, while spiral welded pipes can also use automated submerged arc welding, the welding angle and position change continuously as the seam spirals around the pipe, resulting in slightly lower stability. LSAW pipes are more reliable in high-pressure, high-stress environments due to the uniformity of their welds.
3. Differences in Forming Precision and Dimensional Stability
3.1. Geometric Precision
LSAW steel pipes are formed using multiple pre-bending and pressing rollers, ensuring a short forming path that allows for strict control of roundness, straightness, and edge flatness. Spiral welded pipes, however, involve the rolling of steel strips at varying angles, which can lead to slight waves or roundness deviations. For large-diameter pipes, the cumulative error in the forming process may become more pronounced in the length direction.
3.2. End Quality
The ends of LSAW pipes are cut from steel plates before being formed, which results in high flatness at the ends. Spiral welded pipes, being continuously rolled, have exposed spiral seams after cutting, which may affect the end stability. End quality directly impacts the efficiency of subsequent welding, flange connections, and field installation.
4. Differences in Non-Destructive Testing (NDT) Processes
4.1. Weld Seam Inspection Focus
LSAW steel pipes have concentrated weld seams, which allows for efficient, precise inspection methods such as linear ultrasonic testing or X-ray inspection, covering the entire weld range in a single scan. In contrast, the spiral seams of spiral welded pipes are longer, requiring more complex and longer inspection paths. The changing angle of the weld also complicates the reflection and attenuation of ultrasonic waves, making testing more challenging. Therefore, LSAW steel pipes provide more stable quality control and reliable inspection results.
4.2. Full-Size Inspection Coverage
In large-diameter LSAW pipe production, 100% weld seam non-destructive testing is typically carried out, and the inspection area can be accurately localized. While spiral welded pipes also undergo full inspection, the spiral welds introduce more variables in the test results. For projects with strict quality requirements, reducing quality risks is crucial, making LSAW pipes more controllable in terms of testing outcomes.
5. Comparison of Production Efficiency and Process Stability
5.1. Differences in Production Pace
LSAW steel pipes are made from fixed-length steel plates, with each plate corresponding to one pipe, resulting in a more predictable and consistent production pace. Spiral welded pipes, however, are produced continuously, which is more suitable for long-distance, large-volume manufacturing. However, when frequent changes in specifications are required, LSAW steel pipes offer more flexibility and consistency in adjusting parameters.
5.2. Process Stability
LSAW steel pipes have concentrated control points in their forming and welding processes, leading to higher process stability. In contrast, spiral welded pipes, with their continuous rolling method, may experience fluctuations in steel strip tension and angle changes, which can affect forming quality. For high-demand projects, process stability is a key consideration.
6. Manufacturing Process Advantages Driven by Application Demands
6.1. Manufacturing Requirements for High-Pressure Conditions
LSAW steel pipes are better suited for high-pressure, high-stress, and long-distance pipelines, such as those used in oil and gas transmission networks, thanks to their straight weld seams, concentrated welding energy, and uniform weld structure. Spiral welded pipes, due to their longer weld seams, are relatively less reliable under extreme pressure conditions.
6.2. Advantages in Large-Diameter and Thick-Walled Manufacturing
LSAW steel pipes can easily achieve large diameters and thick-walled specifications, offering strong plate-forming capability and welding reliability. In projects with ultra-thick walls and large diameters, the straight-weld structure of LSAW pipes better distributes stress, making them more suitable for offshore engineering, deepwater pipelines, and urban pressure pipeline networks.
7. Conclusion
There are significant differences between the manufacturing processes of longitudinal submerged arc welded steel pipes and spiral welded pipes, particularly in terms of forming methods, welding structure, geometric precision, non-destructive testing, and process stability. Overall, LSAW steel pipes, with their shorter weld seams, stable forming, precise testing, and ability to meet the demands of thick-walled and large-diameter projects, are more competitive in high-requirement engineering fields. Spiral welded pipes excel in continuous production and large-batch supply, but are more suited for applications where extreme pressure or high-strength requirements are not critical. The choice of manufacturing process is driven by the specific needs of the project, but for applications emphasizing reliability and high strength, LSAW steel pipes remain the preferred option.
