Steel pipes are mainly divided into two categories: seamless steel pipes and welded steel pipes, with significant differences in their manufacturing processes.
The following are the main production processes and their characteristics:
Seamless Steel Pipe Manufacturing Process
1. Hot-Rolled Seamless Steel Pipes (Main Method)
a.Applicable Pipes: Medium to large diameter, thick-walled pipes
b.Process Flow:
| Billet Preparation | Cut round bars (carbon steel/alloy steel) and heat to 1200°C. |
| Piercing | Use a slant rolling piercing machine to pierce solid billets into hollow rough tubes (Mannesmann piercing method). |
| Rolling | Wall thickness reduction and elongation via a continuous rolling mill/expanding mill. |
| Sizing | Control of outer diameter precision. |
| Cooling and straightening | Straightening after water cooling to eliminate stress. |
| Inspection and storage | Ultrasonic testing, hydrostatic testing, dimensional inspection. |
c.Features:
Suitable for high-pressure, high-temperature environments (e.g., oil casing, boiler tubes).
Dense microstructure, but higher cost.
2. Cold-drawn/cold-rolled seamless steel tubes
a.Applicable tubes: small-diameter, high-precision, thin-walled tubes.
b.Process flow:
| Hot-rolled tube blank | First undergoes hot rolling to obtain a rough tube. |
| Acid washing and lubrication | Removes scale and applies phosphating solution to reduce friction. |
| Cold deformation |
Cold drawing: Reduces diameter through die drawing (multiple passes possible). Cold rolling: Thins wall thickness using rollers (e.g., two-roll periodic cold rolling mill). |
| Heat treatment | Annealing to eliminate work hardening. |
| Finishing | Straightening, polishing, and inspection. |
c.Features:
Smooth surface and high dimensional accuracy.
Suitable for precision applications such as hydraulic cylinders and bearing sleeves.
Welded Steel Pipe Manufacturing Process
1. High-Frequency Straight Seam Welded Pipe (ERW)
a.Applicable Steel Pipes: Low-pressure fluid conveyance (e.g., water, gas)
b.Process Flow:
| Coil Unwinding | Steel strip (JIS G3131/SPHC) is unwound and flattened. |
| Forming | The strip is bent into a circular tube shape using multiple rollers. |
| High-frequency welding | 150–400 kHz current melts the edges, and pressure is applied to weld them. |
| Removal of internal and external burrs | A scraper removes weld spatter. |
| Sizing and cooling | Roundness is controlled, and water cooling is used to set the shape. |
| Inspection | Eddy current testing (ET) and hydrostatic testing. |
c.Features:
High efficiency and low cost.
Weld seam strength can reach over 90% of the base material.
2. Spiral welded pipe (SSAW)
a.Applicable steel pipes: large diameter, oil and gas long-distance transmission pipelines.
b.Process flow:
| Steel strip delivery | Continuous steel strips are coiled at a spiral angle. |
| Double-sided submerged arc welding | internal welding + external welding, with filler metal applied. |
| Expansion | Mechanical expansion to eliminate residual stress. |
| X-ray inspection | Ensures welds are free of porosity and inclusions. |
c.Features:
Can produce ultra-large diameter pipes .
Long welds result in lower pressure-bearing capacity compared to straight seam pipes.
3. Submerged arc welded straight seam pipe (LSAW)
a.Applicable steel pipes: thick-walled, high-pressure pipes (such as submarine pipelines).
b.Process flow:
| Steel plate milling | JCOE or UOE forming (pre-bending → gradual pressing forming). |
| Pre-welding | Gas shielded arc welding (GMAW) for fixed weld seams. |
| Multi-wire submerged arc welding | 4–5 wires in series (deep penetration, high efficiency). |
| Expansion + heat treatment | Improves mechanical properties. |
c.Features:
Pressure resistance is close to that of seamless pipes, making it suitable for critical engineering projects.
High equipment investment, suitable for small batch customization.
Summary
Seamless steel pipes: The preferred choice for high-pressure, high-temperature scenarios, but costly.
Welded steel pipes: Cost-effective, suitable for low-pressure, high-volume requirements.
The choice of process should be based on a comprehensive consideration of factors such as diameter, pressure, and budget.
We are able to provide high quality steel pipes according to customers' needs and look forward to your purchase.
