Coupled Stress-Strain and Temperature Simulation Analysis of Steel Pipe Oblique Rolling Process

Literature Overview

This research by Shuang Yuanhua, Lai Mingdao, and Zhang Zhongyuan, published in Forging and Stamping Technology (2003, Vol. 28, No. 6, pp. 36-40), presents a finite element analysis of the oblique rolling (plattner-type) process for steel pipe manufacturing. The key contribution is the coupling of stress-strain and temperature fields during the rolling simulation, providing more accurate predictions of the deformation process and offering a basis for roll and mandrel wear analysis.

Technical Methodology

The study employs a thermo-mechanically coupled finite element approach to simulate the oblique rolling process. The coupling framework accounts for:

• Thermo-mechanical coupling: Plastic deformation generates heat (adiabatic heating), which in turn affects material flow stress through temperature-dependent constitutive relationships.
• Material model: Temperature-dependent stress-strain curves are incorporated, reflecting the reduction in flow stress at elevated deformation temperatures.
• Boundary conditions: Realistic constraints representing roll contact, mandrel guidance, and friction conditions are applied.
• Validation: Calculated entry and exit temperatures are compared against measured values, demonstrating good agreement between simulation and experiment.

Key Technical Parameters and Process Windows

Stress-Strain-Temperature Coupling Analysis

The coupled simulation reveals several important phenomena:

1. Thermo-mechanical feedback loop: As the steel pipe blank is reduced in cross-section between the rolls, plastic work converts to heat, raising the local temperature. This temperature increase reduces the flow stress, allowing further deformation at lower loads. The coupled simulation captures this self-reinforcing mechanism that uncoupled analyses miss entirely.
2. Temperature distribution non-uniformity: The outer surface of the pipe experiences higher temperatures due to frictional heating at the roll contact zone, while the inner surface (mandrel contact) exhibits a different thermal profile. This temperature gradient creates differential flow stresses across the wall thickness, influencing final wall thickness uniformity.
3. Roll and mandrel wear correlation: The stress distribution at the roll-pipe and mandrel-pipe contact interfaces directly correlates with wear patterns. High contact stress regions correspond to accelerated wear, while the temperature field influences wear mechanisms (adhesive wear at high temperatures versus abrasive wear at lower temperatures).
4. Entry and exit temperature prediction: The simulation accurately predicts the thermal state at process entry and exit, with calculated average temperatures matching measured values. This validates the thermal model and provides confidence in using simulation results for process optimization.

Process Optimization Implications

The coupled analysis provides several actionable insights for steel pipe manufacturing:

• Roll wear prediction and management: By identifying high-stress, high-temperature contact zones, operators can implement targeted roll maintenance schedules. Critical wear zones can be monitored using dimensional gauging at specific circumferential positions.
• Temperature control strategy: The simulation identifies optimal temperature windows for achieving desired mechanical properties. Excessive temperatures (>1100°C) may cause grain coarsening, while insufficient temperatures (<800°C) increase rolling forces and may cause cracking.
• Mandrel design optimization: Understanding the stress distribution on the mandrel surface enables improved mandrel material selection and surface treatment strategies. Hardened surfaces or thermal barrier coatings can extend mandrel life in high-temperature contact zones.
• Pass schedule optimization: The coupled model can be used to optimize multi-pass rolling schedules, balancing deformation efficiency with thermal management to achieve target dimensions and properties.

Quality Control Considerations

From a quality control perspective, the coupled simulation results inform several inspection and verification activities:

• Dimensional verification: Wall thickness uniformity around the circumference should be checked at multiple stations along the pipe length, as temperature non-uniformity may cause localized thinning.
• Surface quality inspection: Excessive temperatures at the roll contact zone may cause surface burns or decarburization. Visual inspection and, for critical applications, metallographic examination of the surface layer are warranted.
• Microstructural verification: For alloy pipes, the final grain size and phase composition should be verified through metallographic analysis, as the coupled temperature history directly influences the cooling transformation behavior.
• Residual stress assessment: The non-uniform deformation and temperature distribution may create significant residual stresses. Ultrasonic stress measurement or X-ray diffraction methods can quantify these stresses in critical applications.

Study Insights and Manufacturing Practice

This coupled simulation approach represents a significant advancement over uncoupled thermal or mechanical analyses. For steel pipe manufacturers, the ability to predict temperature evolution alongside stress-strain states enables more accurate process design and quality prediction. The validation against measured temperatures provides confidence that the simulation can be used for virtual process development, reducing the need for expensive trial rolling runs.

The practical implication is that process engineers can use coupled simulation results to optimize roll geometry, speed settings, and temperature control strategies before committing to production runs. This is particularly valuable for new product development (e.g., alloy pipes or specialized service conditions) where the process window may be narrow and trial-and-error approaches are impractical.

The study also highlights the importance of accurate material property databases for coupled simulations. Temperature-dependent flow stress curves, thermal conductivity, specific heat, and emissivity data must be characterized for each steel grade to ensure simulation accuracy. Manufacturers investing in comprehensive material characterization will gain a competitive advantage in process optimization and quality assurance.