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Always up to date. In this column you can find the steel pipe related articles, including industry trends, product standards and materials, and some technical guidelines.
During the extrusion process, spiral welded steel pipes (SSAW pipes) experience a complex coupled stress field dominated by thermal stress and radial compressive stress. The stress distribution closely correlates with temperature gradients inside the pipe structure.
1. Temperature Evolution During Extrusion
As extrusion progresses, the inner lining temperature of the spiral welded steel pipe increases continuously.
At the final stage of extrusion, the temperature near the extrusion die on the inner wall of the lining reaches approximately 631 °C.
The intermediate lining layer and the outer cylinder show no significant temperature variation throughout the process.
The temperature field exhibits a clear axial and radial gradient, with the highest values concentrated near the die-contact region.
2. Equivalent Stress Distribution Under Different Working States
The equivalent (von Mises) stress of the spiral welded steel pipe varies significantly depending on the operating condition:
- Non-working state:
Maximum equivalent stress: 243 MPa
Stress location: inner wall surface
- Preheated state:
Maximum equivalent stress: 286 MPa
Stress location: middle region of the inner wall lining
- Working (extrusion) state:
Maximum equivalent stress: 952 MPa
Stress location: high-temperature zone at the upper end of the inner wall
The stress concentration zones overlap strongly with high-temperature regions, indicating that thermal stress induced by temperature differences is the dominant factor governing stress distribution during extrusion.
- Engineering insight:
Thermal gradients, rather than mechanical load alone, control the peak stress levels inside SSAW pipes.
3. Radial Stress Characteristics of Spiral Steel Pipe
Radial stress behavior changes distinctly across operating states:
- Non-working state:
Dominated by external prestress
Radial stress state: compressive
Maximum value: 113 MPa, located on the outer wall
- Preheating state:
Maximum radial pressure: 124 MPa
Concentration zones: upper and lower end faces
- Working state:
Maximum radial pressure: 337 MPa
Concentration zone: upper section of the spiral steel pipe
With increasing temperature and extrusion load, radial compressive stress intensifies and shifts toward the high-temperature working region.
Summary
Stress concentration in spiral welded steel pipes during extrusion is temperature-driven.
The inner wall near the extrusion die is the most critical structural zone.
Thermal stress dominates equivalent stress evolution under working conditions.
Radial stress remains compressive but increases sharply during active extrusion.
FAQ
Q: What dominates stress in SSAW pipe extrusion?
A: Thermal stress from temperature gradients.
Q: Where is peak stress located during extrusion?
A: Inner wall near the extrusion die.
Q: Maximum equivalent stress in working state?
A: About 952 MPa.
Q: Is radial stress tensile or compressive?
A: Compressive in all states.
Q: What increases radial stress during extrusion?
A: Rising temperature and extrusion load.
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